Introduction to bacteria

Introduction to bacteria

1. Test A. 1st person to actually see living microorganisms was ………………………………… B. What term did he gave to the microorganisms?- ………………………………………………. 2. Who coined the term vaccine?- ………………………………………………. 3. Nucleoid is present in- ………………………………………………. 4. 5 Hallmarks of life.   5. Biologists consider viruses to be non-living because

2. Bacteria Ribosome Cytoplasm Nucleoid Glycocalyx Cell wall Cytoplasmic membrane Flagellum Inclusions

3. Prokaryotes Bacteria were first discovered in the late 1600’s by Antony van Leeuwenhoek , using the microscope he invented. (1674) The first recorded observation were of the bacteria found in the dental plaque of two old men who never cleaned their teeth.

4. Bacteria are prokaryotic microorganisms and are called as prokaryotes SIZE : 0.2 to 2.0 μm in diameter and from 2 to 8 μm in length. surface area/ volume ratio is exceedingly high favoring unusually high rate of growth and metabolism of bacteria No circulatory mechanism is needed to distribute the nutrients that are taken in, due to this high surface to volume ratio

5. Bacterial Morphology Shape : coccus (spheres) and bacillus (rods ). Spirillum (spiral) is less common. Aggregation of cells : single cells, pairs (diplo), chains ( strepto ), clusters ( staphylo ). Thus we have types such as diplococcus (pair of spheres) and streptobacillus (chain of rods).

6. Shape and arrangement Division in one plane produces diplococci and streptococci. (b)Division in two planes produces tetrads. (c)Division in three planes produces sarcinae and (d) Division in multiple planes produces staphylococci

7. Bacilli (a) Single bacilli (b) Diplobacilli (c) Streptobacilli (d) Coccobacilli

8. M ost bacteria are monomorphic Some bacteria, such as Rhizobium and Corynebacterium are genetically pleomorphic .

9. In bacteria, the cell wall is composed of peptidoglycan . Archaean cell walls - glycoprotein S-layers , pseudopeptidoglycan , or polysaccharides . Fungi possess cell walls made - chitin , Algae typically possess walls made of glycoproteins and polysaccharides . Diatoms have a cell wall composed of biogenic silica .

10. Glycocalyx and capsule Many prokaryotes secrete on their surface a substance called glycocalyx If the substance is organized and is firmly attached to the cell wall , the glycocalyx is described as a capsule

11. It is termed a microcapsule if it is too thin to be seen by light microscopy The material is called “ Slime ” if the layer is abundant and many cells are embedded in a common matrix Functions of capsule : In certain species, capsules are important in contributing to bacterial virulence (the degree to which a pathogen causes disease) Protect pathogenic bacteria from phagocytosis by the cells of the host They may block attachment of bacteriophages They may provide protection against temporary drying by binding water molecule They may promote attachment of bacteria to surfaces

12. Flagella and motility hair like helical appendages protrude through the cell wall responsible for swimming motility Bacteria that lack flagella are referred to as atrichous Flagella may be peritrichous (distributed over the entire cell) polar (at one or both poles or ends of the cell) If polar, flagella may be monotrichous (a single flagellum at one pole) lophotrichous (a tuft of flagella coming from one pole) amphitrichous (flagella at both poles of the cell)

13. Arrangements of bacterial flagella

14. Parts of flagella a) Basal body associated with cytoplasmic membrane and cell wall b) a short hook c) A helical filament which is usually several times longer than the bacterial cell The hook and filament are made up of protein whereas the composition of basal body is not known. The protein of the filament is known as flagellin . One advantage of motility is that it enables a bacterium to move toward a favorable environment or away from an adverse one

15. Taxis . Chemotaxis and Phototaxis If the chemotactic signal is positive , called an attractant , the bacteria move toward the stimulus If the chemotactic signal is negative , called a repellent, the bacteria move away from the stimulus

16. Fimbriae and pili Used for attachment and transfer of DNA rather than for motility They are hollow, non-helical filamentous appendages that are more numerous than flagella These structures, which consist of a protein called pilin arranged helically around a central core, are divided into two types Fimbriae Pili Fimbriae can occur at the poles of the bacterial cell or can be evenly distributed over the entire surface of the cell

17. Pili Pili are usually longer than fimbriae and number only one or two per cell. Pili are involved mostly in DNA transfer . Conjugation sex pili (F Pili) . The exchanged DNA can add a new function to the recipient cell, such as antibiotic resistance or the ability to digest its medium more efficiently .

18. Sheaths Sheath is a hollow tube formed in some species of bacteria to enclose chains of bacterial cells. Sheath is commonly found in the species from fresh water and, marine environments

19. Cell Wall In bacteria the cell wall is very rigid and gives the shape to the cell It accounts for 10-40% of dry weight of the cell Cell wall composition of eubacteria is different from that of archaebacterial Eubacteria cell wall is made up of peptidoglycan ( murein ) and insoluble, porous cross linked polymer of enormous strength and rigidity

20. Peptidoglycan is basically a polymer of N- acetylglucosamine (NAG), N- acetylmuramic acid (NAM), L- alanine, D-alanine, D-glutamate and a diamino acid. The peptidoglycan is present only in prokaryotes. Gram positive and Gram negative type of bacteria are present in both eubacteria and archaebacteria N- acetylglucosamine (NAG) and N- acetylmuramic acid (NAM) joined as in a peptidoglycan. The gold areas show the differences between the two molecules. The linkage between them is called a β -1,4 linkage

21. The cell walls of archaebacterial , e.g., Methanobacterium and some other methane-generating archaea (methanogens) are generally made up of pseudomurein . Gram staining is one of the most important and widely used differential staining introduced by Christian Gram in 1884. Bacteria stained by Gram’s staining method fall into two groups – Gram positive , (which appear deep violet in color) and Gram negative (which appear red in color). Gram staining is generally not applicable to other microorganisms. However, yeasts consistently stain gram positive

22. In Gram-positive bacteria, the purple crystal violet stain is trapped by the layer of peptidoglycan which forms the outer layer of the cell. In Gram-negative bacteria, the outer membrane of lipopolysaccharides prevents the stain from reaching the peptidoglycan layer . The outer membrane is then permeabilized by acetone treatment, and the pink safranin counterstain is trapped by the peptidoglycan layer.

23. Differences in the cell wall of Gram positive and Gram negative eubacteria

24. Outer membrane of Gram negative bacteria The lipopolysaccharide (LPS) of the outer membrane is a large complex molecule that contains lipids and carbohydrates and consists of three components: lipid A a core polysaccharide an 0 polysaccharide (O antigen)

25. Cytoplasmic membrane This is about 7.5 ηm thick and is immediately beneath the cell wall This is primarily composed of phospholipids (20-30%) and proteins (60-70%) This membrane contains various enzymes involved in respiratory metabolism and in the synthesis of capsular and cell wall components It is the site of generation of proton motive force, which drives ATP synthesis, certain nutrient transport systems and flagellar motility Damage to this membrane may result in the death of the cell

26. Metabolic Diversity Bacteria show far more metabolic diversity than eukaryotes General classification, based on carbon (food) source and energy source. autotroph vs. heterotroph (fungi) phototroph vs. chemotroph Photoautotrophs ( Purple bacteria, Cyanobacteria) Photoheterotrophs ( a rare category) ( purple non- sulfur bacteria , green non- sulfur bacteria , and heliobacteria ) Chemoautotrophs ( methanogens , halophiles , sulfur oxidizers and reducers , nitrifiers , anammox bacteria, and thermoacidophiles ) Chemoheterotrophs get both energy and organic compounds from other organisms. We are chemoheterotrophs .

27. Relationship to Oxygen For more than half of Earth’s history, oxygen wasn’t present in the atmosphere. Many bacteria evolved under anaerobic conditions. Classification: strict aerobes (need oxygen to survive) strict anaerobes (killed by oxygen) aerotolerant (don’t use oxygen, but survive it). facultative anaerobes (use oxygen when it is present, but live anaerobically when oxygen is absent).

28. Spores Some bacteria can form very tough spores, which are metabolically inactive and can survive a long time under very harsh conditions. Spores can also survive very high or low temperatures and high UV radiation for extended periods.

29. Spores Spore is a metabolically dormant form, which under appropriate conditions can undergo germination and grow out to form a vegetative cell Spores produced within the cell are called endospores and the spores produced external to cell are called exospores

30. Archaea Sometimes called “ Archaebacteria ” One distinguishing characteristic: cell membranes don’t contain fatty acids , but instead use branched molecules called isoprenes . Three main type: methanogens, extreme halophiles, extreme thermophiles .

31. Methanogens Methanogens: convert hydrogen and carbon dioxide into methane to generate energy anaerobically . Methanogens are obligate anaerobes : they are killed by oxygen. Methanogens digest cellulose in cow and termite guts. Each cow belches 50 liters of methane a day. A major greenhouse gas .

32. Halophiles Extreme halophiles. Grow in very salty conditions . Colorful bacteria Mostly aerobic metabolism. Some have a form of photosynthesis that uses bacteriorhodopsin , a pigment very similar to the rhodopsin pigment in our eyes. It is also called “purple membrane protein” Slight halophiles- 2-5% ( Erythro

33. Thermophiles Extreme thermophiles. Live at very high temperatures : ocean hydrothermal vents (up to 113 o C, which would be boiling except for the high pressure under the ocean), hot springs in Yellowstone National Park. Use sulfur to generate energy just like we use oxygen: donate electrons to sulfur to create hydrogen sulfide. Some generate sulfuric acid instead—they live at very low pHs .

34. Eubacteria The most common types of bacteria Many categories: we will just look at a few of them. Enteric bacteria live in the digestive tracts of animals. Enterics are facultative anaerobes. Best known example: Escherichia coli (E. coli ), found in the human gut and also used as a common experimental organism in the lab. Related enteric bacteria: Salmonella, Shigella . Cause food poisoning. Chickens carry Salmonella in their guts instead of E. coli .

35. Endospore-forming Bacteria Most of these are in the genus Bacillus (named after their normal shape). Their spores are very resistant to environmental conditions, and may survive millions of years before they revive. Anthrax is caused by a Bacillus species. Also is this family are the bacteria that cause botulism (a very bad form of food poisoning) and tetanus (lockjaw--the muscles go rigid).

36. Nitrifying and Nitrogen-fixing Bacteria The atmosphere is 80% nitrogen . However, we can’t directly use atmospheric nitrogen, because it is in the wrong form: N 2 . We need it in the ammonia form: NH 3 . Nitrogen fixing bacteria are able to do this conversion . Most of them live in root nodules of certain plants, the legumes, such as alfalfa and soybeans. Plants also need nitrogen in the form of nitrate, NO 3 . Nitrifying bacteria convert ammonia into nitrate.