An account of Prokaryotic classification
- 1. An account of Prokaryon Devlina Sengupta Kanchrapara College Department of Microbiology
- 3. Types of Archaebacteria 1) Methanogens 2) Halophiles 3) Thermoacidophiles • Methanogens and Halophiles are placed in division Euryarchaeota • While Thermoacidophiles are placed in division Crenarchaeota
- 4. How many Bacterial Phyla are there? • Largest taxon under domain for prokaryotes is the phylum (no kingdoms for prokaryotes) • 36 bacterial phyla with cultured represntatives listed in LPSN. 10 more in LPSN have Candidatus status • Between 80-90 identified based on rRNA from heterogenous samples. Members have never been cultured or characterized beyond their small subunit rRNA • Number always increasing • Hundreds to thousands are estimated to exist • Almost all (90%) characterized species are in 4 phyla: Proteobacteria, Actinobacteria, Firmicutes, Bacteroidetes
- 6. General features • Best characterized phylum 30% of characterized species are here • All gram-negative • Metabolically, morphologically diverse • 6 classes 1. Alphaproteobacteria- 2nd largest, 1000 known species 2. Betaproteobacteria- 3rd largest, 500 known species 3. Gammaproteobacteria- largest, over 1500 known species 4. Deltaproteobacteria 5. Epsilonproteobacteria 6. Zetaproteobacteria- Only 1 known species
- 7. Alphaproteobacteria • Most are aerobes & prefer low nutrient environments • 10 orders (order names always end in –ales) • Rhizobiales- largest, most diverse 1. Has phototrophs, chemolithotrophs, nitrogen fixers, methylotrophs 2. Named for Rhizobia, nitrogen fixers living in legume root nodules 3. Genus Bartonella includes human pathogens (Legionnaire’s disease, cat scratch fever) • Rickettsiales- obligate intracellular parasites or mutualists (Genus Rickettsia includes human pathogens (typhus, RM spotted fever) • Genus Rhodobacter & Rhodospirillum- purple nonsulfur bacteria • Genus Sphingomonas- metabolize many organic pollutants, useful in bioremediation
- 8. Betaproteobacteria • High metabolic diversity • 6 orders • Burkholderiales- very diverse a) Includes phototrophs, chemolithotrophs, nitrogen fixers b) Genus Burkholderia useful for bioremediation (removes heavy metals, toxic hydrocarbons, and more) • Rhodocyclales- very diverse a) Genus Rhodocyclus- Purple nonsulfur bacteria b) Genus Zoogloea- important for wastewater treatment 9removes/precipitates organics) • Neisseriales- Chemoorganotrophs a) Genus Neisseria- contains human pathogens(meningitis, Gonorrhea) • Hydrogenophilales- Contains sulfur oxidizers, denitrifyers, autotrophs • Methylophilales- methylotrophs(no methanotrophs) • Nitrosomonadales- ammonia oxidizers
- 9. Gammaproteobacteria • Very diverse • Phototrophs (purple sulfurs), chemolithotrophs • 12 orders • Enterobacteriales- best characterized, called enteric bacteria a) Facultatively aerobic chemoorganotrophs living in intestines, soil & water b) Many genera contain human pathogens. Mutualists (live in helpful symbiotic relationship) Pathobionts( mutualists that can be pathogenic under wrong circumstances) • Escherichia coli- best characterized microbial species
- 10. Gammaproteobacteria 2 • Important Enterobacteriales genera 1. Salmonella- many pathogens (typhoid fever) 2. Escherichia- usually mutualists (UTIs & O157:H7) 3. Shigella- many pathogens (dysentery) 4. Proteus- many pathobionts (UTIs) 5. Enterobacter- usually mutualists 6. Klebsiella- nitrogen fixers, rarely pathogenic (Pneumonia) 7. Serratia- pathobiont that can cause nosocomial(hospital-related) infections 8. Yersinia-some serious pathogens (Black Death)
- 11. Gammaproteobacteria 3 • Pseudomonadales- aerobic chemoorganotrophs a) Genus Pseudomonas has human pathogens; P.aeruginosa is multi-drug resistant and causes nosocomial infections • Vibrionales- aerobic or fermentative chemoorganotrophs a) Generally aquatic, many bioluminescent species with Vibrio shape b) Genus vibrio contains human pathogens (Cholera)
- 12. Deltaproteobacteria • 8 orders • 5 orders starting with ‘Desulf’-are sulfur- reducers and/or metal-reducers a) Frequently live together with Epsilonproteobacteria • Myxococcales and Bdellovibrionales- predators • Syntrophobacterales- syntrophs that produce H2 and live with secies that consume it a) Otherwise the reaction is too unfavourable
- 13. Epsilonproteobacteria • 1 order • Campylobacterales a) Many sulfur-oxidizers b) Frequently live together with Deltaproteobacteria • Many Spirilla a) Genus Campylobacter contains human pathogens (food-borne illness) b) Genus Helicobacter contains human pathogens (Stomach ulcers) • Many in this class are only known by rRNA
- 14. Spirochetes • Genetically & morphologically distinct group of bacteria • Thin spiral shaped or wave like bacteria that are highly motile • Endoflagella/ periplasmic flagella provide them with cork screw like motility especially for propelling through highly slimy intestinal mucus • They differ from typical gram negative cells in ultrastructure • They are chemo organotrophic that possess both pathogenic & non-pathogenic members • Medically important genera of Spirochaetes include: Borrelia, Leptospira, Treponema • An extraordinary location for them is on the surfaces of some the cellulose-digesting protozoa found in termites
- 15. Firmicutes, Tenericutes, Actinobacteria (Gram-positive bacteria)
- 16. Firmicutes, Tenericutes, Actinobacteria • Together contain about half of characterized species • All gram-positive • Firmicutes and Tenericutes are low GC gram positive bacteria a) They have little Gs and Cs in their DNA • Actinobacteria are high GC gram-positive bacteria a) They have lots of Gs and Cs in their DNA
- 17. Firmicutes • 7 classes, 3 important orders • Lactobacillales- lactic acid bacteria (produce lactic acid in fermentation) a) Important for food production (milk, yougurt, pickles, etc) b) Aerotolerant anaerobes that metabolize sugars c) Genus Lactobacillus- acidophilic, nonpathogenic, many are microbiome members d) Genus Streptococcus- some human pathogens (Strep throat)
- 18. Firmicutes 2 • Bacillales- some can form endospore a) Genus Listeria contains human pathogens (food-borne illness) • Genus Staphylococcus are halophilic/halotolerant a) Contains members of skin microbiome (some pathobionts) b) MRSA is a multi-drug resistat strain of S.aureus • Genus Bacillus forms endospores a) Contains human pathogens (anthrax) b) Some produce antibiotics • Clostridiales- some can produce endospores a) Contains human pathogens (tetanus, botulism, C.difficile causes drug-resistant nosocomial diarrhea)
- 19. Tenericutes • 1 class, Mollicutes • Called mycoplasmas after genus Mycoplasms • No cell walls, have sterols and lipoglycans in membrane • More variable shapes due to no cell wall • Most live in hosts
- 20. Actinobacteria • 6 classes, 9 orders • Actinomycetales a) Genus Corynebacterium uses snapping division, resulting in V-shape and palisade arrangements b) Genus Propionibacterium members cause acne and are useful in cheese production • Genus Mycobacterium has waxy cell walls, some grow very slowly a) Contains human pathogens (tuberculosis, leprosy) • Genus Streptomyces forms hyphae, is single largest source of antibiotics
- 21. Bacteroidetes • Over 700 known species • 7 classes, 7 orders • Gram-negative • Many can degrade complex polysaccharides • Bacteroidales- most are obligate anaerobes (fermenters) a) Genus Baccteroides live in intestines of animals as commensals (live in neutral symbiotic relationships)/mutualists b) Also can be pathobionts if they leave intestines c) Flavobacteriales- common in cold waters, many are psychrophiles or psychrotolerants
- 22. Chlamydiae • Gram-negative, obligate intracellular parasites • Very small genomes that include some eukaryotic genes a) Gained from hosts by horizontal gene transfer • 1 class, 1 order (Chlamydiales) • 2 life stages a) Elementary body- used to travel between host cells b) Reticulate body- when living in host cell • Genus Chlamydia contains human pathogens (Chlamydia, trachoma)
- 23. Planctomycetes • Gram-negative, unusual morphology a) Usually have stalks/appendages, use budding division b) Many have intracellular membrane invaginations c) Some have archaeal S layer • 2 classes, 3 orders • Pirellulosome- structure containing nucleoid and ribosomes, enclosed by membrane folds • Anammoxosome- organelle for ammonia oxidation (only some have)