Topic 7: Bacterial MVPs Flashcards
Purple Bacteria
Purple Sulfur and Purple Nonsulfur Bacteria:
- Anoxygenic photosynthesis (no oxygen produced — H2O not source of e−)
- O2 inhibits photosynthesis, but some can grow aerobically using respiration
- Bacteriochlorophylls and carotenoid pigments determine the wavelengths of light used for photosynthesis. Intracytoplasmic membranes hold light-harvesting molecules
- Photoautotrophs oxidize H2S to S^0 during photosynthetic CO2 reduction
- S^0 is stored in periplasm or externally
- Found in anoxic zones of lakes where H2S present
Purple nonsulfur bacteria prefer very low levels of H2S
A Winogradsky column can be used to grow purple bacteria (Sulfate reducers, Green sulfur, Purple sulfur bacteria, Purple non-sulfur bacteria, Cyanobacteria and algae)
Methylotrophs & Methanotrophs
Methyl: bacteria that can oxidize one carbon (C1) compounds, no C-C bonds, non organic compounds
methylotrophs that use methane are called methanotrophs
Metha: able to oxidize methane because have enzyme that is important for the process called methane monooxygenase, or MMO
- obligate aerobes
- found in aquatic and terrestrial habitats (between anoxic zones, where methane is formed, and in oxic zones, where O2 is available for respiration), cattle rumen, swamps
Nitrifiers
- autotrophic, often use ammonia (nh3) as source of energy and electrons, converting it to nitrite (no2)
- Nitroso
- others use nitrite and convert to nitrate (no3)
- Nitro
- Nitrosococcus is a good example of an ammonia oxidizer;
- Nitrobacter is a good example of a nitrite oxidizer
- Chemolithoautotrophs
- Widespread distribution: found in wastewater treatment plants, soils, lakes, sediments
- Ammonia oxidizers contain the enzyme ammonia monooxygenase, which is used to oxidize ammonia to nitrite. These enzymes are housed in extensive intracytoplasmic membranes (membranes inside the cell) and are evolutionarily related to methane monooxygenase (see methanotrophs above).
- Nitrite oxidizers contain the enzyme nitrite oxidoreductase (Nxr)
Pseudomonads
- Very heterogeneous group, taxonomy has been revised recently
- Aerobic chemoorganoheterotrophs
- Nutritionally versatile
- Polar flagella
- Inhabit many different environments (e.g., soil, water, animal pathogens, plant pathogens)
- Some produce a siderophore called pyoverdin (fluorescent), which is used to acquire iron from the environment
Enteric Bacteria
All within the Gammaproteobacteria
Peritrichous flagella, facultative, oxidase negative, simple nutritional requirements (i.e., not fastidious)
Includes many pathogens, therefore very well studied
Coliforms represented within the enterics — these are key fecal organisms (as well as being plant saprophytes), and these are used as evidence for fecal input in aquatic environments. Their presence indicates the potential for the presence of pathogens
Nitrogen-fixing Bacteria
Free Living Aerobic N2-Fixing Bacteria
- Strict aerobes
- Able to fix N2 aerobically although the nitrogenase enzyme, which reduces N2 to NH3, is irreversibly inactivated by O2
- Have thick slime layer and very high rate of respiration, which together keep the intracellular O2 concentration low during N2 fixation
Rhizobia (symbiotic N2-fixing Bacteria)
- Strict aerobes in the Alphaproteobacteria
- Forms an infectious thread in leguminous plants (e.g., clover, soybean) and cells differentiate within a root nodule
- Oxygen provided to nodules by plant’s leghemoglobin
- Photosynthates (organic acids) delivered to rhizobia to fuel nitrogen fixation via the TCA cycle
- Root nodules provide fixed nitrogen (ammonia or amino acids) to the host plant
Contrast the steps involved in Agrobacterium and rhizobial symbioses with plants
Agrobacterium
- members of the alphaproteobacteria
- gram-negative aerobic rods
- parasitic relationship with plants
- causes crown gall tumors on plants
- it can infect plants because it is encoded by a plasmid inside of their cells
- T-DNA is transferred into the plant nucleus to integrate into the chromosome of the plant
- genes on T-DNA produce phytohormones which cause the plant to start dividing and develop the tumours
- then every tumour cell is busy making modified AAs called opines which are food that only the agrobacteria can consume
- they do inter-kingdom genetic transfer (bacteria able to send DNA from a bacterial cell into a eukaryotic cell)
Rhizobium (Root nodule formation)
- multistep process
- mutualistic relationship
- plants and rhizobia initiate a relationship when the plants need more nitrogen
- the plant sends out a message using flavonoids to find a suitable rhizobium cell
- if you have the correct rhizobia near the plant root then the cell will send out a response signal by producing nod factor
- root cells form leghemoglobin to assist
- the plant must have both the flavonoids and the nod factor to allow the cell to get inside it and divide
- it grows along an infection thread where it finds a nodule to proliferate inside
- they differentiate, get larger and rounder and are now permanently N2 fixers for the plants
Deltaproteobacteria: Bdellovibrio bacteriovorus
- bacteria eater
- small, highly motile with one flagella
- vibroid shape (curved rod, small spiral)
- preys on other gram-negative bacteria (ex. E.coli, pseudomonas)
- virus-like life cycle
- chemoorganoheterotroph
Life Cycle:
- 100 cell lengths per second (very fast at attacking their prey)
- when they strike their prey, they attach and go through the outer membrane, cell wall and into the periplasm where they excrete hydrolytic enzymes that degrade everything in the cytoplasm and
- cells of Bdellovibrio get longer and longer because eats all the nutrients and material in cytoplasm
- 2.5-4h per cycle
- then separates into 3-6 progeny per lysis
Deltaproteobacteria: Gliding Myxobacteria
- savage, killing machines
- complex behaviour and development; send out scouts into the environment that move along away from the colony searching for anything to eat
- can report their findings back by sophisticated intracellular communication system
-very large chromosomes with so many genes (2x as big as E.coli) - vegetative cells exhibit gliding motility over surfaces; obtain nutrients by lysing other bacterial cells
- chemoorganoheterotrophs
- when there is a lack of food they produce pigmented fruiting bodies filled with myxospores
- found on decaying wood, dung pellets
Explain how Staphylococcus and Micrococcus are ideal skin inhabitants
- Staphylococcus species from the Firmicutes have low GC content genomes.
- Micrococcus is from the Actinobacteria, with high GC content genomes
- aerobic metabolism
- catalase positive
- very resistant to desiccation (process of removing moisture form something) and are tolerant to very high salt concentrations (7.5%)
- share pigmentation
- above is ideal for organisms that must inhabit the surface of our skin, which is a very dry and high-salt environment
Lactic Acid Bacteria
(Streptococcus and Lactococcus)
- Rods and cocci
- Produce lactic acid as major fermentation product
- No electron transport system, therefore only substrate-level phosphorylation (fermentation)
- Anaerobes, but aerotolerant
- Complex nutritional requirements; limited biosynthetic capacity (fastidious)
- Heterofermenters differ from homofermenters in pathways and end products (produces only lactic acid)
- Involved in many processes that are of human interest
— Pathogens, fermented products, oral health, yogurt
Bacillus
- Facultative or obligate aerobes
- Can break down complex polymers
- Many produce antibiotics
- Some species produce crystal protein toxins that kill insect larvae — many are specific for a particular type of insect (BT toxin)
- Some species can infect humans and other animals (e.g., Bacillus anthracis)
- have big genomes to do this all
Clostridium
- Strict anaerobes
- no electron transport system
- Diversity of anaerobic fermentation (substrate and product)
- Many industrially important products
- Some fix N2
- Some produce toxins that cause human disease
- used for botox (clostridium botulinum)
Mycobacterium and other actinomycetes
- Cell wall contains lipids called mycolic acids
- Exhibit acid-fastness, a property in which the dye basic fuchsin is not removed by acid-alcohol wash due to interaction of mycolic acids with the dye
- Resistant to many chemicals because of high mycolic acid content of cell wall
- Some are human pathogens
—– Mycobacterium tuberculosis causes tuberculosis
—– Mycobacterium leprae likely causes leprosy
Filamentous Actinobacteria
- Nutritionally versatile bacteria
- Filamentous; form branching mycelia
- Form spores called conidia
- Conidia are formed in sporophores, which are aerial filaments that are important for traditional classification of these bacteria
- Produce geosmins, which provide soil with its characteristic earthy smell
- Produce antibiotics
- Important genus is Streptomyces, members of which are found mostly in the soil and produce many important antibiotics
