Lec 6: Diversity of Gram -ve bacteria Flashcards
Gram -ve bacteria groups
Based on 16s rRNA studies
Non-Proteobacteria
Proteobacteria
Green sulphur bacteria (phylum chlorobi)
Non-proteobacteria
Photosynthetic bacteria
Anoxygenic photosynthesis (do not evolve O2)
Deposit sulphur granules outside cell
Chromosomes contain photosynthetic pigments
Net-like structure
Phylum Cyanobacteria
Non-proteobacteria
Photosynthetic bacteria
Largest, most diverse group of photosynthetic
Oxygen photosynthesis (evolve O2)
Development of life on earth: endosymbiosis of cyanobacteria evolved into chloroplast
Unicellular or filaments: vary in appearance
Thylakoid membrane carries our photosynthesis
Some have heterocysts (specialised cells. Fix N2 -> convert to NH3 to build AA)
Some develop into heterocysts if no nitrate or ammonia available
In most waters, soils
Can form ‘blooms’. Fertiliser allows rapid growth -> growth of chemoheterotrophic bacteria -> deplete O2 -> kill fish
May produce toxins -> kill livestock and other animals that drink water
Genus Chlamydia
Phylum Chlamydiae
Non-proteobacteria
Gram -ve cocci
Obligate intracellular parasites (reproduce only in host cell) of mammals, birds
Chlamydia trachomatis
Phylum Chlamydiae
Trachoma (bacterial infection)
Most common cause of preventable blindness in humans
Phylum Spirochaetes
Non-proteobacteria
Gram -ve
Flexible helical cells
Axial fibrils (periplasmic flagella) -> corkscrew like motility through liquids and crawling on solid media
Treponema pallidum
Phylum Spirochaetes
Cause of syphilis (contagious STD)
Proteobacteria
Largest, most diverse group of bacteria
16s sequencing -> 5 subgroups (alpha, beta, gamma, delta, epsilon
Sometimes called purple bacteria (purple photosynthetic bacteria in alpha, beta and gamma)
Alpha proteobacteria
Most oligotrophic: live in low nutrient environment
Some with distinctive morphology
Some pathogens
Some with unusual metabolic modes
Some photosynthetic bacteria
Include world’s most abundant group of bacteria
Genus Caulobacter
Alpha proteobacteria
Gram -ve
Have a prostheca or stalk -> attachment to surfaces and nutrient uptake
Oligotrophs
In marine & fresh water, soil
Genus Rickettsia
Gram -ve
Small rods, cocci or pleiomorphic
Obligate intracellular parasites
Rickettsia prowazekii
Alpha
Typhus: high fever, rash, stupor
Genus Rhizobium
Alpha
Gram -ve rods
Aerobic, motile
Infect roots of leguminous plants
Form root nodules: plant & bacteria symbiotic relationship. Bacteria fix (reduce) N2 to NH3 -> N available to plant host
Genus agrobacterium
Alpha
Cause crown gall tumours in plants
Cancer causing bacterium
Same family as Rhizobium, both
Genus Neisseria
Beta proteobacteria
Gram -ve
Aerobic diplococci
Inhabit mucus membranes of mammals
Neisseria meningitidis
Cause of meningitis (inflammation of brain or spinal cord)
In nose or throat
Neisseria gonorrhoeae
Cause gonorrhoea (STD)
Gamma proteobacteria
Largest subgroup of proteobacteria
Some photosynthetic bacteria
Facultatively anaerobic chemoheterotrophs
Aerobic chemoheterotrophs
Genus Pseudomonas
Gamma
Gram -ve
Aerobic respiration
Motile with 1 or more polar flagella
In soil & water
Many degrade wide range of organic substrates
Important in medicine, industry & environment
Pseudomonas aeruginosa
Infects people with lowered resistance, burns, wounds, and has high antibiotic resistance
Genus Vibrio
Gamma
Gram -ve
Curved rods (comma shaped)
Facultative anaerobes
Aquatic, marine habitats
Other species cause fish diseases
Vibrio cholerae
Cholera: watery profuse diarrhoea
Family: enterobacteriaceae
Gram -ve
Gamma
Straight rods
Facultative anaerobes
Simple nutritional requirements (ferment glucose & other carbohydrates)
Motile with peritrichous flagella (uniformly distributed over body surface)
Inhabit intestinal tracts
Genus Escherichia
Family Enterobacteriaceae
Common inhabitant of human gastrointestinal tract
Commensal (symbiotic relationship)
Strains cause: gastroenteritis (traveller’s diarrhoea), urinary tract infections, haemolytic uraemic syndrome -> kidney failure
