Microbes of Extreme Environment Microbial Interaction.pptx

Microbes of Extreme Environment & Microbial Interaction

1. Microbes of Extreme Environment & Microbial Interactions Priya Dixit Department of Biotechnology Era University, lucknow

2. What are Microbes Types of Microbes Microbes are Extreme E nvironment • Thermophiles • Psychrophiles • Halophiles • Acidophiles • Alkaliphiles

3. What are microbes • Microbes are living organisms, so tiny you can’t see them without a microscope. • They are so small we need a microscope to see them. • They are different shapes and sizes. • They are found EVERYWHERE! • Some microbes are useful or even good for us. • Some microbes can make us ill. Types of microbes There are 5 main types of microbes Bacteria Virus Fungi Algae Protozoa

4. BACTERIA VIRUS Fungi Algae Protozoa

5. What are extreme environments? An extreme environment is a habitat characterized by harsh environmental conditions further than the optimal range for the development of humans or other living organisms. Extreme environments are characterized by various unfavorable conditions including, high or low temperature, high or low pressure, and acidic or basic pH. For an area to be considered extreme, certain conditions or aspects of the environment must be considered very hard for different forms of life to survive. Examples of some extreme environments include the polar region, deserts, volcanic regions, deep ocean trenches, outer space, and every other planet of the Solar System except the Earth. Some of the common extreme environments include areas that are alkaline, acidic, extremely hot or cold, high salt concentration, without water or oxygen.

6. Extreme environments are classified into the following groups based on the extreme physicochemical conditions: Extreme temperature:  Two types of extreme environments can be described; cold and hot. Extremely cold environments are those with environmental temperatures below 5°C. These can be found in deep ocean niches, at the peaks of high mountains, or the Polar Regions. Extremely hot environments are characterized by environmental temperatures higher than 45°C. These environments are influenced by geothermal activity as geysers and fumaroles of continental volcanic areas or deep-sea vents. Extreme pH:  Extreme environments can also be classified as acidic or alkaline according to their pH. Extreme acidic environments are natural habitats in which the pH is below 5. Extreme alkaline environments are those with a pH above 9. Extreme ionic strength: Hypersaline environments are environments with an ionic concentration higher than of seawater (greater than 3.5%). Extreme pressure: Extreme pressure environments are those environments under extreme hydrostatic or litho pressure, such as aquatic habitats at depths of 2,000 m or more or deep-subsurface ecosystems. High-radiation environments  are those areas that are exposed to abnormally high radiation doses, including ultraviolet or gamma radiation, like deserts and the top of high mountains. Xeric environments  are arid habitats with limited water activity. Cold and hot deserts are some examples of these extreme environments.

7. What are extremophiles? Extremophiles are living organisms with the ability to survive and thrive in extreme environments as a result of different physiological and molecular adaptations. These organisms thrive in extreme niches, ice, and salt solutions, as well as acid and alkaline conditions. Some might grow in toxic waste, organic solvents, heavy metals, or in several other habitats that are considered inhospitable for life. Most extremophiles are prokaryotic organisms with few eukaryotes. These extremophiles are defined by the environmental conditions in which they can survive and thrive optimally. Extremophiles can be divided into two categories: extremophilic organisms that require one or more extreme conditions to survive, and extremotolerant organisms that can tolerate extreme conditions of one or more physical parameters even though they grow optimally at neutral conditions. Extremophiles include members of all three domains of life; bacteria, archaea, and eukarya . Most extremophiles are prokaryotes with a high proportion of belonging to archaea, but some organisms might be eukaryotes such as protists (e.g., algae, fungi, and protozoa) and multicellular organisms. These are classified according to the conditions in which they grow: thermophiles and hyperthermophiles (organisms growing at high or very high temperatures, respectively), psychrophiles (organisms that grow at low temperatures), acidophiles and alkaliphiles (organisms thriving in habitats with acidic or basic pH values, respectively), barophiles (organisms that grow best under pressure), and halophiles (organisms that grow well in an environment with NaCl). Characteristics of extremophiles Extremophiles are characterized by the ability to thrive in extreme environments which results from different forms of physiological and molecular adaptations. Extremophiles are mostly prokaryotes with the nuclear material in the cytoplasm and unicellular eukaryotes. Archea is an important group of organisms that tend to be extremophiles due to their ability to adapt to different extreme conditions. These organisms present a wide and versatile metabolic diversity, along with extraordinary physiological capacities to inhabit extreme environments. These forms of adaptations are developed through various evolutionary processes over a long period of time.

8. Microorganisms in extreme temperature (Psychrophile/Thermophile/Hyperthermophile) Psychrophile Definition and Characteristics Psychrophiles, literally meaning cold-loving, are organisms adapted to growth at low temperatures, having an optimum growth temperature of greater than 15°C and a maximum growth temperature of greater than 20°C. Psychrophilic microorganisms have successfully colonized all permanently cold environments from the deep sea to mountain and polar regions. With more than 80% of Earth’s biosphere is permanently below 5°C, suitable environments for psychrophiles are widespread and include, among others, ocean waters, permafrost, glaciers, Antarctic rocks, snowfields, and polar ice caps. Some of these organisms, depending on their optimal growth temperature, are also known by the terms psychrotolerant or psychrotroph . Psychrophiles have successfully overcome two main challenges that arise during growth at low temperature: first, low temperature, because any decrease in temperature exponentially affects the rate of biochemical reactions; and second, the viscosity of aqueous environments. Prokaryotic psychrophiles vary in their requirement and indeed tolerance to oxygen and include (strictly) aerobic, (strictly) anaerobic, and facultative species. In addition to extremes of cold, many psychrophiles tolerate or in some cases require other extreme environmental conditions for growth and survival. Deep-sea psychrophiles, for example, may require high pressures for growth, thus making them barophilic psychrophiles. Psychrophile Examples Some common examples of psychrophiles include  Psychrobacter  members of  Halomonas  species, psychrophilic species of  Pseudomonas  and  Alteromonas   sps ,  Hyphomonas   spp ,  Sphingomonas   spp ,  Chryseobacterium   greenlandensis ,  Desulfotalea psychrophila , Psychrobacter arcticus,  etc.

9. Thermophile Definition and Characteristics Thermophiles (literally heat lovers) are organisms that grow at temperatures above those (25–40°C) that sustain most life forms. Typically, a thermophile shows maximum growth rates at temperatures above 45°C. There are many examples of the environment with extreme temperatures. Environments with high temperatures include both terrestrial and submarine environments. Different habitats throughout the world are suitable for the growth of thermophiles. These can range from surface  soil to compost piles. Thermophiles are generally found in areas like thermal vents, hot springs, and boiling steam vents. Thermophiles are further divided into different groups; facultative thermophiles and obligate thermophiles. Facultative thermophiles can thrive at both high and moderate temperatures whereas obligate thermophiles require high temperature for growth. Like in the case of psychrophiles, thermophiles also have different physiological and molecular adaptations that enable the organisms to survive at temperatures that would normally denature proteins, cell membranes, and genetic material. Thermophile Examples Some of the common examples of thermophiles include  Methanosarcina thermophila , Methanobacterium wolfei , Methanobacterium thermoautotrophicum , Archaeglobus profundus , Alicyclobacillus acidoterrestris , A. acidocaidarius , etc.

10. Hyperthermophile Definition and Characteristics Hyperthermophiles are organisms that can survive and grow at extremely high temperatures (above 80°C). Hypothermophiles are a type of thermophiles that can endure even higher temperatures than other thermophiles. The optimum temperature of growth for hyperthermophiles is 80°C, but they can survive at temperatures higher than 100°C. Most hyperthermophiles are capable of withstanding other extreme conditions like higher pH and higher pressure. Most hyperthermophilic organisms are found in hot springs and boiling steam vents where even moderate thermophiles cannot survive or thrive. Hyperthemophiles mostly belong to the archea group with very few species being bacterial species. Hyperthermophile Examples Some of the common examples of hyperthermophilic organisms are  Thermoproteus uzoniensis , Staphylothermus marinus, Pyrodictium abyssi , Pyrococcus furiosus , Hypothermus butylicus , Pryococcus woesei , Pyrodictium brockii , Pyrodictium occultum , etc.

11. Microorganisms in extreme pH (Acidophile/Alkaliphile) Acidophile Definition and Characteristics Acidophiles are organisms that can survive and thrive at highly acidic conditions (usually at pH 2.0). Acidophilic microorganisms thrive in extremely low pH natural and man-made environments such as acidic lakes, some hydrothermal systems, acid sulfate soils, sulfidic regoliths , and ores, as well as metal and coal mine-impacted environments. Highly acidic environments are formed by the oxidation of the metal and other sulfidic minerals that are populated by a range of acidophilic and acid-tolerant prokaryotic and eukaryotic life forms. Heterotrophic, acidophilic bacteria, often living in close association with chemolithotrophic primary producers, have also been isolated from extremely acidic environments. The most widely studied acidophiles are prokaryotes that oxidize reduced iron and sulfur. They can catalyze the oxidative dissolution of metal sulfide minerals such as pyrite (FeS 2 ), thereby severely acidifying the environment (often to pH less than 3) in which they thrive. There are several natural acidic environments that include volcanic areas, hydrothermal sources, deep-sea vents, metal mining areas, and the stomachs of animals. Acidophilic organisms belong to all three domains of life; archaea, bacteria, and eubacteria, but archaea represent the largest acidophilic group of organisms. Physiologically, the acidophiles are very diverse: aerobic and facultative anaerobic, chemolithotrophs, and different types of heterotrophic prokaryotes, photoautotrophic eukaryotes, predatory protozoa, and others. Acidophile Examples Some examples of acidophilic organisms include Lactobacillus,  Thiobacillus sulfolobus , Bacillus acidocaldarius , Thermoplasma acidophilus, Picrophilus , Ferroplasma acidiphilum , Acidithiobacillus , Leptospirillum , Acidobacteriu m spp.,  Sulfobacillus , etc.

12. Alkaliphile Definition and Characteristics Alkaliphiles are a group of extremophiles that can live and thrive in environments with extremely high pH value (9-13) with the optimal pH being 10. Alkaliphiles are of two types; obligate alkaliphiles growing only in environments with pH higher than 9 and facultative alkaliphiles that can live both at neutral pH and alkaline conditions. Most of the organisms described to date as growing under very alkaline conditions are prokaryotes, comprising a heterogeneous collection of eubacteria with a few examples of archaebacteria. Alkaliphiles can be isolated from ‘normal’ environments such as garden soil presumably because there are transient alkaline conditions generated in such environments by biological activity. Alkaliphiles are believed to be the earliest life forms on Earth which originated billions of years ago in deep-ocean alkaline hydrothermal vent systems. Alkaliphiles thrive in many geographical locations across the planet, both in natural and manmade alkaline environments like alkaline soda lakes, soda deserts, and saline soda soils. Other natural habitats in which alkaliphiles flourish include the alkaline serpentine lakes, oceanic bodies, ikaite tufa columns, and alkaline hydrothermal vents. Alkaliphile Examples Some of the examples of alkaliphiles include  Bacillus alkaliphilus , Bacillus pasteurri , Bacillus halodurans , Halobacterium, Clostridium paradoxum , Halomonas pantelleriensis , Alkaliphilus hydrothermalis , etc.

13. Microorganisms in extreme low humidity/water activity ( Xerophiles ) Xerophile Definition and Characteristics Xerophiles are a group of extremophiles that are capable of surviving in environments with low availability of water or low water activity. Generally, xerophilic organisms are capable of growing at a w  values lower than xerotolerant organisms (a w  below 0.8). Two major types of the environment provide habitats for the most xerophilic organisms, namely foods preserved by some form of dehydration or organic solute-promoted lowering of a w  and saline lakes, where low a w  values are a consequence of inorganic ions. In environments where little water is available, organisms must take up and maintain sufficient water against extreme concentration gradients to support cellular processes. Xerophiles are of different types belonging to different groups of living beings. Xerophilic fungi represent a large group of xerophilic organisms. Eukaryotic organisms like plants capable of surviving at low water condition, called xerophytes are also xerophiles . Xerophiles are closely related to halophiles as halophilic environments tend to have low water activity. Even though water is crucial for many biomolecular processes in living beings, xerophiles have intricate means to survive in conditions with low water activity. Xerophile Examples Some common examples of xerophiles are  Aspergillus penicillioides , Cereus jamacaru , Deinococcus radiodurans , Aphanothece halophytica , Anabaena, Bradyrhizobium japonicum, Saccharomyces bailli , etc.

14. Microorganisms in extreme salinity (Halophiles) Halophile Definition and Characteristics Halophiles are a group of extremophiles that require high salt concentrations for their survival and growth. Halophiles are of two types; obligate halophiles that require NaCl concentration of 3% or more and halotolerant that survive at both average salt concentrations and higher. Halophilic microorganisms constitute the natural microbial communities of hypersaline ecosystems, which are widely distributed around the world. The general features of halophilic microorganisms are low nutritional requirements and resistance to high concentrations of salt with the capacity to balance the osmotic pressure of the environment. The salt requirement in halophiles is classified into three groups; low (1-3%), moderate (3-15%), and extreme (15-30%). Salt requirement depends on factors like temperature, pH, and growth medium. They are physiologically diverse; mostly aerobic and as well anaerobic, heterotrophic, phototrophic, and chemoautotrophic. Ecologically, the halophilic microorganisms inhabit different ecosystems characterized by a salinity higher than seawater that range from hypersaline soils, springs, salt lakes, sabkhas to marine sediments. These organisms are found in all three domains of life, i.e., Archaea, Bacteria, and Eukaryota . Halophilic bacteria are more abundant in specific phylogenetic subgroups, most of which belong to Halomonadaceae , a family of Proteobacteria. Halophile Examples Some common examples of halophilic organisms in terms of their salt requirement are: Slightly halophilic:   Erwinia, Bacillus hunanensis , Halomonas zhaodongensis , Alkalibacterium thalassium , etc. Moderately halophilic:   Spiribacter salinus , Halobacillus sediminis , Halobacillus salicampi , Marinobacter piscensis , Idiomarina aquatica , etc. Extreme halophile:   Halococcus salifodinae , Halobacterium salinarum , Limimonas halophilia , Lentibacillus kimchii , Sporohalobacter salinus , etc.

15. Microorganisms in extreme sugar concentrations ( Osmophiles ) Osmophile Definition and Characteristics Osmophiles are a group of organisms that are adapted to survive in environments with high osmotic pressures like high sugar concentration. Osmophilic organisms are similar to halophiles, and xerophiles as all of them have the capacity to survive in environments with low water activity. Osmophiles are mostly found in food with high sucrose content and environments with high osmolarity. Fungi are the most common group of organisms that survive as osmophiles . However, organisms of the group Archea and Bacteria are also important osmophiles . Osmophilic organisms are found in different parts of the world, especially in areas with high sugar content like food sources. The ability to adapt to fluctuations in external osmotic pressure and the development of specific mechanisms to achieve the adaption is fundamental to the survival of cells. Most cells maintain an osmotic pressure in the cytoplasm that is higher than that of the surrounding environment, resulting in an outward-directed pressure, turgor, whose maintenance is essential for cell division and growth. Any changes in environmental osmolarity can trigger the flux of water across the cytoplasmic membrane.  Thus, osmophilic organisms develop different mechanisms to overcome the osmotic imbalance. Osmophile Examples Some common examples of osmophiles include  Zygosaccharomyces, Torula, Schizosaccharomyces octosprus , etc.

16. Microorganisms in extreme pressure (Piezophiles/ Barophiles ) Piezophile Definition and Characteristics Barophiles are defined as organisms that grow and thrive optimally at pressures greater than atmospheric pressure. The term piezophile is used as a replacement to barophile as piezo means pressure in Greek. Barophilic bacteria have been isolated from various deep-sea environments throughout the world and have been grown rapidly at low temperatures and high pressures. Bacteria living in the deep-sea display several unusual features that allow them to thrive in their extreme environment. Most barophilic organisms tend to be psychrophilic and thus cannot be cultured at a temperature above 20°C. Similarly, many barophiles tend to be obligate barophiles with few archaea acting as moderately barophilic. It has been seen that the pressure needed for the maximal rate of reproduction at 2°C may reflect the true habitat depth of an isolate. High pressure affects the survival of microorganisms, where it influences the membrane structure and functioning of the cell. High pressure and low temperature in deep-sea environments decrease the fluidity of lipids and even depress the functions of biological membranes. Piezophile Examples Some common examples of barophilic microorganisms are  Shewanella benthica , Moritella yayanosii , Shewanella violacea , Photobacterium profundum , Moritella japonica, Sporosarcina   spp , etc.

17. Microorganisms in rocks ( Endolith /Hypolith) Endolith  Definition and Characteristics Endolith is an organism that survives in various inhospitable environments throughout the world, especially inside rocks, animal shells, coral reefs, and sand particles in the soil. Endoliths occupy habitats beneath and between porous and translucent rocks and minerals. Rock porosity provides interstitial spaces for microbial colonization and translucence enables photosynthesis to take place. Despite their limited water availability, cold temperature, strong winds, and large variations in solar radiation input, cold deserts harbor endolithic microorganisms. Microbial life can thrive, and endolithic microbial communities have been intensively studied in the Antarctic region, which is characterized by extreme climatic conditions, with low humidity and precipitation making it practically an inhospitable environment for living beings. In terrestrial systems, these microenvironments typically provide protection from intense solar radiation and desiccation, as well as sources of nutrients, moisture, and substrates derived from minerals. In marine systems, endolithic communities similarly exploit the rocky seafloors, but also dwell into limestone and mineralized skeleton of a broad range of marine animals. Besides tolerating the desiccating conditions and extreme temperatures, microorganisms inhabiting such arid conditions are subjected to osmotic stress due to the high salt concentrations. The water content of sandstone colonized by endolithic microorganisms is represented by 0.1–0.2% by weight as a result of little moisture penetrating into the rocks through pores. Endolith Examples Some examples of endoliths include  Leptolyngbya , Helicobacter recurvirostre , Gloeocapsa sanguine, Acaryochloris , Chroococcidiopsis , Anabaena, Spirirestis rafaelensis , etc.

18. Hypolith Definition and Characteristics Hypoliths are organisms or communities of organisms that live on the underside of rocks or at the rock–soil interface. Hypoliths are photosynthetic microorganisms that exist in hot and arid climates, usually at the interface between the rocks and the soil. The community of microorganisms present in such an area is termed as hypolithon . Microorganisms that are present underneath the rocks are protected from the harsh radiations of the sun and the wind. The rocks might even trap moisture which can then be used by these microorganisms. Different forms of minerals like quartz are found in soil and rocks that also supports different forms of life. However, there are different stresses, including low water activity and drastic changes in temperature, which limits the biodiversity of such habitats. The most common habitats for hypoliths include the desert lands and polar regions where the climate change is quite drastic with rapid desiccation and rehydration. Hypolith Examples Some of the common examples of hypoliths include  Nostoc, Bryum , Hennediella , Stichococcus mirabilis, Ichthyosporea , etc.

19. Microorganisms in heavy metals (Metallotolerant) Metallotolerant Definition and Characteristics Metallotolearnt microorganisms are the microorganisms that are capable of tolerating and detoxifying high levels of dissolved heavy metals. Microorganisms utilize metals as structural components of biomolecules, as cofactors in reversible oxidation/reduction reactions, and in electron transfer chains during energy conservation. However, metals can become toxic if their intracellular concentrations are too high. Most metallotolerant microorganisms tend to be acidophilic as the physiological activities of such microorganisms enable tolerance against high metal concentrations. As many metals are more soluble at acidic pH, acidophiles are typically exposed to high metal concentrations and can survive in 1000-fold higher amounts than neutrophilic microorganisms. Metallotolerant microbes belong to all bacterial groups studied, mostly among aerobic and facultative aerobic chemo-heterotrophic microorganisms. Polluted soils and waters with untreated industrial and urban wastes and samples of the natural environment with a high concentration of metals are important habitats of metallotolerant microorganisms. These organisms have different mechanisms that support their survival in very high metal concentrations. Metallotolerant Examples Some of the common examples of metallotolerant species include  Bacillus subtilis, Bacillus megaterium, Acidithiobacillus ferrooxidans , Acidithiobacillus caldus , Corynebacterium diptheriae , Acidiphilium rubrum, Acidiphilium multivorum , etc.

20. Microorganisms in extreme Radiation ( Radiophiles ) Radiophile Definition and Characteristics Radiophiles are a group of extremophiles that are capable of surviving extreme forms of radiations like ionizing radiant (gamma rays) and UV radiation. Studies on radiophiles are quite limited as they are to be isolated from extreme environments like outer space of other planets. These organisms have low diversity with all organisms belonging to the archaea and bacteria families. Radiophiles can either be radiation tolerant or radiation-resistant. Radiation tolerant microorganisms can endure harmful radiation for a period of time, whereas radiation-resistant organisms can withstand a longer period of time. Radiations are harmful to neutrophils as they destroy various important biomolecules like DNA, proteins, and enzymes as a result of ionization. Non-ionizing radiation, in turn, results in the formation of reactive oxygen species like superoxides which then affects the metabolism of those cells. The adaptive mechanism utilized by radiophiles might be different for ionizing and non-ionizing radiation. Radiophile Examples Some common examples of radiophiles are  Deinococcus radiodurans , Brevundimonas , Rhodococcus , Halomonas , Herbaspirillum , Hymenobacter , Rhodobacter , etc.

21. Applications of Extremophiles Exremophilic enzymes have been model systems to study enzyme evolution, enzyme stability, activity, mechanism, protein structure, function, and biocatalyst under extreme conditions. Thermophiles have yielded stable α-amylase for starch hydrolysis, oxylonases for paper bleaching, and proteases for brewing and for detergent purposes. Alkaline active proteases, amylases, cellulases, mannanases , lipases, etc. are used in the formulation of heavy-duty laundry and dishwashing detergents as they are efficient in removing stains and allow effective low-temperature (30–40°C) washing. Some species of acidophilic microorganisms can be used not only to reduce mine water pollution but also to recover metals from acidic wastewater via selective biomineralization. Extroenzymes like Taq polymerase from  Thermus aquaticus  is an ideal for use in a polymerase chain reaction as it reduces the need for adding extra polymerase during the reaction. Cellulose for various extremophilic organisms has been used for the treatment of juices, color brightening in detergents, and treating cellulose-containing biomass and crops to improve their digestibility and nutritional quality. Similarly, halophiles are being exploited as a potential source of carotene, compatible solutes, glycerols , and surfactants for pharmaceutical use. Some extremophilic microorganisms may also comprise a large reservoir of novel therapeutic agents—for example, iron-binding antifungal compound, pyochelin isolated from halophilic species of  Pseudomonas . A thermostable glucokinase from the thermophilic species,  Bacillus   stereothermphiolus , can be used as a glucose sensor for quick glucose assay. Alkaline active enzymes have got several notable applications in textile and fiber processing in processes like cotton scoring and blast fiber degumming. Alkaliphiles and their enzymes have been tried in various synthesis reactions with peptide synthesis being the most important one. Information on the microbial composition and biogeochemical cycling of extreme ecosystems also helps in understanding the global change, threats, and opportunities for living beings. Enzymes from extremophiles can also be used in bioremediation processes like toxifying wastewater and air and removing metallic waste from sewages and industries. Different barophilic enzymes are used for the production and sterilization of items at varied pressure conditions.

22. Microbial interaction Biological interactions are the effects that the organisms in a community have on one another. There are completely different kinds of microbial interactions which incorporates interaction with different microbes, Plant-Germ interactions promoting plant growth, interaction with animals, interaction with humans, and interaction with water, etc. Microbial interactions are ubiquitous, diverse, critically important in the function of any biological community, and are crucial in global biogeochemistry. The most common cooperative interactions seen in microbial systems are mutually beneficial. The interactions between the two populations are classified according to whether both populations and one of them benefit from the associations, or one or both populations are negatively affected. There are many sorts of symbiotic relationships such as mutualism, parasitism, amensalism , commensalism and competition, predation, protocooperation between the organisms.

23. Types of Microbial Interaction Positive interaction:  Mutualism, Syntrophism , Proto-cooperation, Commensalism Negative interaction:   Ammensalism (antagonism), parasitism, predation, competition 1. Mutualism It is defined as the relationship in which each organism in interaction gets benefits from the association. It is an obligatory relationship in which mutualist and host are metabolically dependent on each other. A mutualistic relationship is very specific where one member of the association cannot be replaced by another species. Mutualism requires close physical contact between interacting organisms. The relationship of mutualism allows organisms to exist in a habitat that could not be occupied by either species alone. The mutualistic relationship between organisms allows them to act as a single organism. Examples of mutualism: Lichens:  Lichens are an excellent example of mutualism. They are the association of specific fungi and certain genus of algae. In lichen, the fungal partner is called mycobiont and algal partner is called phycobiont is a member of cyanobacteria and green algae Symbiosis is a close relationship between two species in which at least one species benefits. For the other species, the relationship may be positive, negative, or neutral. M utualism, Commensalism, and Parasitism are belong in symbiosis .

24. 2. Syntrophism It is an association in which the growth of one organism either depends on or improved by the substrate provided by another organism. In  syntrophism , both organisms in association get to benefit from each other. a. Methanogenic ecosystem in a sludge digester Methane produced by methanogenic bacteria depends upon interspecies hydrogen transfer by other fermentative bacteria. Anaerobic fermentative bacteria generate CO2 and H2 utilizing carbohydrates which are then utilized by methanogenic bacteria ( Methanobacter ) to produce methane. b.  Lactobacillus  arobinosus  and  Enterococcus faecalis In the minimal media,  Lactobacillus  arobinosus  and  Enterococcus faecalis  are able to grow together but not alone. The synergistic relationship between  E. faecalis  and  L.  arobinosus  occurs in which  E. faecalis  require folic acid which is produced by  L.  arobinosus  and in turn, lactobacillus require phenylalanine which is produced by  Enterococcus faecalis .

25. 3. Protocooperation It is a relationship in which an organism in an association is mutually benefited with each other. This interaction is similar to mutualism but the relationships between the organisms in protocooperation are not obligatory as in mutualism. Examples of Protocooperation: a. Association of  Desulfovibrio  and  Chromatium :  It is a protocooperation between the carbon cycle and the sulfur cycle. b. Interaction between N2-fixing bacteria and cellulolytic bacteria  such as  Cellulomonas . 4. Commensalism It is a relationship in which one organism (commensal) in the association is benefited while another organism (host) of the association is neither benefited nor harmed. It is a unidirectional association and if the commensal is separated from the host, it can survive. Examples of commensalism: a. Non-pathogenic  E. coli  in the intestinal tract of humans:  E. coli  is a facultative anaerobe that uses oxygen and lowers the O2 concentration in the gut which creates a suitable environment for obligate anaerobes such as Bacteroides.  E. coli  is a host which remains unaffected by Bacteroides. b. Flavobacterium (host) and  Legionella pneumophila  (commensal):  Flavobacterium excretes cystine which is used by  Legionella pneumophila  and survives in the aquatic habitat. c. Association of  Nitrosomonas  (host) and  Nitrobacter  (commensal) in Nitrification:  Nitrosomonas  oxidize Ammonia into Nitrite and finally,  Nitrobacter  uses nitrite to obtain energy and oxidize it into Nitrate.

26. 5. Amensalism (antagonism) When one microbial population produces substances that are inhibitory to other microbial population then this interpopulation relationship is known as Ammensalism or Antagonism. It is a negative relationship. The first population which produces inhibitory substances are unaffected or may gain competition and survive in the habitat while other populations get inhibited. This chemical inhibition is known as antibiosis. Examples of the antagonism ( amensalism ): a. Lactic acid produced by lactic acid bacteria in the vaginal tract:  Lactic acid produced by many normal floras in the vaginal tract is inhibitory to many pathogenic organisms such as  Candida albicans . b. Skin normal flora:  Fatty acid produced by skin flora inhibits many pathogenic bacteria in the skin c.  Thiobacillus thiooxidant :  Thiobacillus  thioxidant  produces sulfuric acid by oxidation of sulfur which is responsible for lowering pH in the culture media which inhibits the growth of most other bacteria. 6. Competition The competition represents a negative relationship between two microbial populations in which both the population are adversely affected with respect to their survival and growth. Competition occurs when both populations use the same resources such as the same space or same nutrition, so, the microbial population achieves lower maximum density or growth rate. Microbial population competes for any growth-limiting resources such as carbon source, nitrogen source, phosphorus, vitamins, growth factors etc. Competition inhibits both populations from occupying exactly the same ecological niche because one will win the competition and the other one is eliminated. Examples of competition: a. Competition between  Paramecium caudatum   and  Paramecium aurelia :   Both species of  Paramecium  feeds on the same bacteria population when these protozoa are placed together.  P. aurelia  grow at a better rate than  P.  caudatum  due to competition.

27. 7. Parasitism It is a relationship in which one population (parasite) get benefited and derive its nutrition from other population (host) in the association which is harmed. The host-parasite relationship is characterized by a relatively long period of contact which may be physical or metabolic. Some parasite lives outside the host cell, known as ectoparasite while other parasite lives inside the host cell, known as endoparasite. Examples of parasitism: a. Viruses : Viruses are an obligate intracellular parasite that exhibits great host specificity. There are many viruses that are parasite to bacteria (bacteriophage), fungi, algae, protozoa etc. b.  Bdellovibrio :   Bdellavibrio  is ectoparasite to many gram-negative bacteria. 8. Predation It is a widespread phenomenon when one organism (predator) engulf or attack other organisms (prey). The prey can be larger or smaller than the predator and this normally results in the death of the prey. Normally predator-prey interaction is of short duration. Examples of Predation: a. Protozoan-bacteria in soil:  Many protozoans can feed on various bacterial population which helps to maintain the count of soil bacteria at optimum level b.  Bdellovibrio , Vamparococcus , Daptobacter ,   etc are examples of predator bacteria that can feed on a wide range of the bacterial population.