Other Bacteria Flashcards
Cyanobacteria
Oxygenic phototrophs – Most species are obligate phototrophs – Important in producing O2 in the early earth atmosphere – Have a common ancestor with the endosymbiont that gave rise to chloroplasts
- Morphologically diverse – Unicellular and filamentous forms
- Many cyanobacteria produce potent neurotoxins – Can cause poisoning during “blooms”
- Found in terrestrial, freshwater & marine habitats
- Peptidoglycan in cell walls • Outer and cytoplasmic membranes • Mucilagenous envelopes/sheaths – Form clusters of cells • Gas vesicles are found in many cyanobacteria – Help maintain buoyancy – Keep cell in water column where there is light • Heterocysts are rounded, enlarged cells – Anoxic environment inside heterocyst – Site for Nitrogen fixation – Nitrogenase is sensitive to oxygen • Many cyanobacteria display gliding motility
Photosynthesis in Cyanobacteria
• Thylakoids – Intracellular membranes – Location of protein complexes involved in photosynthesis and respiratory electron transport chains • Light harvesting pigments – Phycobilins (accessory pigment) – Chlorophyll a • Have a common ancestor with the endosymbiont that gave rise to chloroplasts
Lichen
Symbiosis between a fungus and a phototrophic organism – Algae or cyanobacteria – Often cyanobacteria that can fix N2 – Fungus gains organic matter from photosynthesis – Bacterium (or alga) gains anchorage, water and inorganic nutrients, protection from desiccation
Spirochetes
• Gram-negative, motile, and tightly coiled – Treponema – flat wave form – Others are helical • Widespread in aquatic environments and in animals
Treponema – Host-associated spirochetes that are commensals or parasites of humans
• Many species – cause of syphilis (T. pallidum) – Some species are commensals in the mouth – Some species found in rumen • Ferment plant polysaccharides
Protoplasmic cylinder enclosed by cell wall and membrane • Outer sheath – Flexible – lipid, protein and carbohydrate • Endoflagella – One or many – Located in the periplasm
Motility in Spirochetes
• Endoflagella are anchored at one end • Motility is by flexing or lashing motion – Endoflagella rotate rapidly – Protoplasmic cylinder rotates in the opposite direction – Cell under torsion • Can move in highly viscous, gel-like medium – e.g connective tissue
Chlamydia
Gram negative type cell walls – Does not stain with Gram stain – Outer lipopolysaccharide membrane – Lacks peptidoglycan. • Obligate parasites – Poor metabolic capacities – Require biosynthetic intermediates and probably ATP – Some of the simplest biochemical capacities of all known bacteria
Chlamydia trachomatis genome sequence
Small genome • Missing genes for biosynthesis of substances supplied by host • Genes for peptidoglycan synthesis and ATP are present – However there is no biochemical evidence for the presence of peptidoglycan – It is not clear that Chlamydia generate ATP • Some genes acquired by horizontal transfer from eukaryotes
The Infection Cycle of Chlamydia
- Elementary body – ~0.3 µm – Rigid cell wall – Infectious – Compact DNA – RNA:DNA 1:1 – Metabolically inactive
- Reticulate body – ~1 µm – Fragile cell wall – Non infectious – RNA:DNA 3:1 – Metabolically active – Encodes a T3SS effectors modify host
