Proteobacteria Flashcards
Phylogenetic overview of Proteobacteria
- Proteobacteria – A major lineage (phyla) of Bacteria – Includes many of the most commonly encountered bacteria – Most metabolically diverse of all Bacteria
- E.g., chemolithotrophy, chemoorganotrophy, phototrophy – Morphologically diverse – Divided into five classes
- Alpha-, Beta-, Delta-, Gamma-, Epsilon-
Pseudomonas and the Pseudomonads
All genera within the Pseudomonad group are: – Straight or curved rods with polar flagella – Chemoorganotrophs – Obligate aerobes – Nutritionally versatile – Ecologically important organisms in water and soil – Some species are pathogenic – Includes human opportunistic pathogens and plant pathogens
Pathogenic Pseudomonas
- Pseudomonas aeruginosa – Infections of urinary and respiratory tract – Infections of burn wounds – Lung infections in people suffering with Cystic Fibrosis – Resistant to antibiotics (R plasmid)
- Other Pseudomonas species – Plant pathogens – Yellow lesions of dead tissue – Hypersensitivity response in tobacco (prevents further – Spread of infection)
- Pseudomonas are capable of breaking down many compounds to non toxic compounds – Includes those that are not naturally occurring – Pesticides – Dyes – Heavy metals – Oil
Enteric Bacteria
• Relatively homogeneous phylogenetic group – Includes E. coli • Facultative aerobes – Respiration – Ferments sugars producing a mixture of acids, H2 and CO2 • May be motile • Nonsporulating rods • Possess relatively simple nutritional requirements
Escherichia coli – Universal inhabitants of intestinal tract of humans and warm-blooded animals • May synthesize vitamins for host – Some strains are pathogenic • E.g. O157:H7 • Salmonella and Shigella – Closely related to Escherichia – Usually pathogenic
Vibrio
• Cells are motile, straight or curved rods • Facultative aerobes / fermentative metabolism • Most inhabit aquatic environments (fresh water or marine) • Vibrio cholerae causes cholera in humans – More in Medical Microbiology and Infection • Some are capable of light production – bioluminescence – Catalyzed by luciferase – Regulation is mediated by population density (quorum sensing)
Bioluminescent Bacteria: Vibrio fischeri
Emit light • Associated with fish – Light organ develops when colonised by bacteria • Symbiotic relationship – Host provides nutrients and shelter – Luminescence can be used for communication and to hide the host from predators below
Bioluminesence
• Requires – Enzyme luciferase – Long chain aliphatic aldehyde e.g. dodecanal (RCHO) – Flavin mononucleotide (FMN) – Oxygen
FMNH2 + O2 + RCHO => FMN + RCOOH + H2O + Light
Regulation of bioluminescence: quorum sensing
- Luciferase only expressed when cells are at high density – High density achieved in light organ
- Bacteria produce an autoinducer (homoserine lactone) – Diffuses out of the cell
- In sea water – Bacterial population density is low – HSL concentration is low – LuxR represses expression of LuxI – No HSL produced, no luciferase produced
Spirilla: Bdevellovibrio
• Prey on other bacteria • Small – 0.3µm in diameter (cf E. coli 0.5µm) • Small genome • Highly motile • Obligate aerobes • Widespread in soil and water, including marine environments
Developmental Cycle of Bdellevibrio bacteriovorus
Attachment and penetration OM of host – Resides in periplasm – Breaks down peptidoglycan – assimilates organic compounds from the prey cytoplasm
- Bdellevibrio elongates without dividing
- Cell division occurs once nutrients are used up – Filament divides – Differentiation into motile forms – Bdellevibrio released
Spirilla: Campylobacter and Helicobacter
- Motile
- Microaerophilic – Require O2 at lower than atmospheric concentrations (3-15%)
- Most species are pathogenic to animals or humans
- Campylobacter* – Enteritis (bloody diarrhoea)
- Helicobacter* – Causes gastritis and peptic ulcers – Can survive the acidic conditions of the stomach – More in Medical Microbiology and Infection
Gliding Myxobacteria
• Gliding Bacteria – Are typically either long rods or filaments – Lack flagella, but can move when in contact with surfaces
• Myxobacteria – Gliding bacteria – Form multicellular structures (fruiting bodies) – Complex developmental life cycles – Chemoorganotrophic soil bacteria – Lifestyle includes consumption of dead organic matter or other bacterial cells
Vegetative cells (a) – Simple, nonflagellated rods – Lysis of other bacteria, use released nutrients • Myxospores (b) – Nutrients depleted – Vegetative cells aggregate – Construct fruiting bodies, – Differentiate into myxospores – Resistant to drying UV and Heat (less resistant than endospores)
Life cycle of Myxococcus xanthus
