Microbial-plant interaction in the environment

Interaction of microbes with plants.
Different types of positive and negative interaction

1. Plant Microbe-Interaction

2. Plant microbe interaction Microbe-plant interactions are critical to plant health, growth, and development. It mainly constitutes the association of microorganism with plants little in a positive way or in a negative way. The positive approach is mainly the symbiotic relationships and the negative approach constituents mainly pathogen plant interactions.

3. Beneficial / positive interactions Neutralism Symbiosis / Mutualism Protoco -operation Communalism a) Neutralism It is a type of neutral association, in two microorganisms behaves entirely independently Each could utilize different nutrients without producing metabolic end products that are inhibitory. This might be transitory as the condition change in the environment, particularly the availability of nutrients, the relationship might change.

4. 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.

5. Examples of mutualism: Lichens:  Lichens are an excellent example of mutualism. They are the association of specific fungi and certain genus of algae. Rhizobium in Root nodules

6. Protocooperation (Synergism) 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 .

7. 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: 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.

8. Negative / harmful / deleterious interactions Detrimental effects of one species on its neighbours are quite common in soil, and they are ditched by the decreases in abundance or metabolic activities of the susceptible organisms. This include Competition Amensalism Parasitism and predation

9. 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. 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.

10. 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.

11. 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.

12. 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

13. Fig. Examples of plant-microbe interactions in the rhizosphere . Plant roots release exudates containing sugars, organic acids, and amino acids that may attract microbes. In exchange, they protect the plant against pathogens releasing antimicrobial compounds; or increase nutrient uptake. On the other hand, these carbon-containing compounds can also attract pathogens. They can compete for nutrients, infect the plant, and affect the rhizosphere microbial community

14. Plant-Microbe Interactions Plant-microbe interactions diverse – from the plant perspective: Negative – e.g. parasitic/pathogenic Neutral Positive – symbiotic  important positive interactions with respect to plant abundance and distribution – related to plant nutrient and water supply: 1. Decomposition 2. Mycorrhizae 3. N 2 fixation 4. Rhizosphere

15. I. Decomposition Raw material or Organic Matter Soil organic matter derived primarily from plants – Mainly leaves and fine roots In a soil which at first has no readily decomposable materials, adding fresh tissue under favorable conditions: 1) immediately starts rapid multiplication of bacteria, fungi, and actinomycetes , 2) which are soon actively decomposing the fresh tissue .

16. 2. Mineralization Breakdown OM  inorganic compounds Microbial process: accomplished by enzymes excreted into the soil Plant uptake Nitrite NO 2 - Nitrate NO 3 - energy for nitrifying bacteria* Nitrification For Nitrogen proteins (insoluble) amino acids energy for heterotrophic bacteria proteases Ammonium NH 4 + Mineralization * In 2 steps by 2 different kinds of bacteria – (1) Nitrosomonas oxidize NH3 to nitrites + (2) Nitrobacter oxidize nitrites to nitrates

17. Symbiotic association between plant roots and fungi. Probably the roots of the majority of terrestrial plants are mycorrhizal . Type of Mycorrhiza 1. Ectomycorrhiza - In which fungal cells form an extensive sheath around the outside of the root with only little penetration into the root tissue itself. 2. Endomycorrhiza - In which the fungal mycelium is embedded within the root tissue. II. Mycorrhiza

18. Mycorrhizae Tree root Mycorrhizal structure Fungal hyphae

19. Fungi-Plant Interaction Mycorrhizae (root fungus) Nearly 90% of native plants have mycorrhiza association Mycorrhiza : Symbiotic relationship between plants (roots) & soil fungi - extension of root system - fungus enhances nutrient and water intake - plants provide carbon source

20. Mycorrhizae - Associations occur exterior root - Develop on evergreen trees and shrubs Ectomycorrhizae Endomycorrhizae - Associations occur in root interior between cells - Develop on deciduous trees, annual and herbaceous plants

21. C. Function of mycorrhizae: Roles in plant-soil interface – Increase surface area & reach for absorption of soil water & nutrients Increase mobility and uptake of soil P Provides plant with access to organic N Protect roots from toxic heavy metals Protect roots from pathogens Effect of soil nutrient levels on mycorrhizae Intermediate soil P concentrations favorable Extremely low P – poor fungal infection Hi P – plants suppress fungal growth – taking up P directly

22. III. N 2 Fixation N 2 abundant – chemically inert N 2 must be fixed = converted into chemically usable form Lightning High temperature or pressure (humans) Biologically fixed The conversion of molecular Nitrogen in to ammonia by microorganism is called as BNF Boussingault (1838). Shows that leguminous plant can fix atmospheric N and increase N content in soil. Better crop rotation involving legumes plant .

23. Examples of plant–N 2 -fixing symbiotic systems – Legumes eg . Peas, Soybeans, Clover s Widespread bacteria = e.g., Rhizobium spp. Those with N 2 -fixing symbionts form root “ nodules ” A. Occurs only in prokaryotes: Bacteria (e.g. Rhizobium , Frankia ) Cyanobacteria (e.g. Nostoc , Anabaena ) Free-living in soil/water – heterocysts Symbiotic with plants – root nodules Loose association with plants Anabaena with heterocysts soybean root

24. IV. Rhizosphere Rhozospere is the soil region in close contact with plant roots Rhizosphere Components – 1. Rhizosphere - The zone of soil influenced by roots through the release of substrates that affect microbial activity . 2. Rhizoplane - Surface of the plant roots in the soil. Rhizoplane is the site of the water & nutrient uptake & the release of exudates in to the soil. 3. Root Itself - It is the part of the system, because certain endophytic microorganisms are able to colonize inner root tissues . The rhizosphere effect can thus be viewed as the creation of a dynamic environment where microbes can develop and interact . This microorganisms play important roles in the growth and ecological fitness of their host.

25. V. Rhizosphere interactions – the belowground foodweb Zone within 2 mm of roots – hotspot of biological activity Roots exude C & cells slough off = lots of goodies for soil microbes  lots of microbes for their consumers (protozoans, arthropods) “Free living” N 2 -fixers thrive in the rhizosphere of some grass species Fine root

26. (1) Removing hydrogen sulfide, which is toxic to the plant roots (2) Increasing solubilization of mineral nutrients (3) Synthesizing vitamins, amino acids,auxins , gibberellins that stimulate plant growth (4) Antagonizing potential plant pathogens through competition and the production of antibiotics Microbial populations in the Rhizosphere may benefit the plant by:

27. Beneficial role of Microbes

28. Bacteria Nitrogen-fixation – convert atmospheric N into useful Nitrogen (N gas  plants  animals) Azotobacter ( Aerobic) and Clostridium ( Anerobic ) genera N fixer Decomposition in the biosphere – get rid of dead organisms, nature’s recyclers Azotobacter common in Rhizosphere maintain roots exudates. Genetically-engineered bacteria produce insulin and other important chemicals. Can also help clean up oil spills: oil ‘eating’ bacteria Organisms present will depend on many factors Nutrients, O2, moisture, pH, Eh, microhabitats .

29. Fungi Decompose carbon compounds Improve OM accumulation Retain nutrients in the soil Bind soil particles Food for the rest of the food web Mycorrhizal fungi Compete with plant pathogens

30. ALGAE Algal Population Imp for soil fertility In barren soil it can bind soil partical To fix atm. N symbiotically or asymbiotically . Population is smaller than bacteria and fungi. Mostly they are present on surface or subsurface of the soil. . BGA used reclamation o akaline soil. The cyanobacteria play a key role in the transformation of rock to soil are Eukaryotic Found in fresh and salt water environments Can live on rocks, trees, and in soils with enough moisture Can carry on photosynthesis – produce large amount of oxygen Diatoms, Clamydomonas, Volvox, Spirogyra

31. Actinomycetes Mostly abundant in surface soil. In soil pH high population very high Take part in decomposition of OM-most active decomposer. eg .- Streptomyces and Nocardia decomposer of cellulose in soil. Act as plant pathogen eg . Potato scab disease ( Streptomyces scabies ) Streptomyces alini is associated in root nodule of Alder plant for N fixation. Antibiosis; Some spp. Of Strptomycesare capable of synthesizing antibiotic. eg : Streptomycin, Chloromphenicol , Cyclohexiamide