Bacterial development - L17

Streptomyces: sporulation as a reproduction mechanism

- Spores can lie dormant in the soil for years (max reported 70 years) - Hydrophobicity is an important characteristic of spores - Hydrophobic proteins called chaplins coat the surface of cells giving them a thick extended outer layer. - Spores are desiccated - High internal concentration of trehalose, a disaccharide of glucose that stabilizes macromolecules during dormancy (then cam be used when germination occurs).

Myxobacteria as predators

Aerobic organoheterotrophs Facultative predators that seek out and feed on other bacteria Can lyse & kill Gram- and Gram+ bacteria & eukaryotic microbes (e.g., yeast, protozoa, fungi, etc.)

Bdellovibrio application

Bdellovibrios prey on various Gram- mammalian pathogens (e.g., E. coli , Salmonella , Legionella ) and biofilms of various Gram negatives. No reports of Bdellovibrio invading Gram+ bacteria or eukaryotic cells. Possible use as a 'live antimicrobial' with therapeutic value? Maybe more likely/acceptable for use on plants; recently tested in chicks infected with Salmonella Used to eliminate biofilms from silicon chips

Bacillus vs. Clostridium

Clostridium: Obligate anaerobes Metabolism- fermentation of sugars and/or proteins Bacillus : aerobes or facultative anaerobes Metabolism- respiration, some can ferment

Sporosarcina general characteristics

Cocci in packets endospore formers Strict aerobes Hydrolyze urea to CO2 + NH3

Bacillus & Clostridium similar characteristics

Common in soil, form endospores Organoheterotrophs Many are polymer degraders Typically motile by peritrichous flagella Some fix nitrogen Some are pathogens Many produce antibiotics

Sporulation Mechanism (Bacillus) What regulates sporulation?

Complex developmental process that requires timed expression of > 200 genes Sensing of environmental conditions: nutrient limitation, population density Once sporulation starts, cells are committed (8 h) Complex decision process: alternatives possible? - upregulation of motility and chemotaxis, transporters, secreted enzymes, antibiotics, competence (DNA uptake) Spo0A-P = master regulator: controls ~120 genes (needs to be phosphorylated to be activated)

Involves asymmetrical cell division and differential gene expression in the forespore and mother cell. How does this happen?

Due to timed transfer of the chromosome from the mother cell, involves sigma factors, anti sigma factors, anti-anti sigma factors In a vegetative cell sigma F factor is always being made but anti-sigma F is present as well so the two interact and turn each other off. anti-anti sigma factor is present as well but since sigma F factor is always being made it is kept in equilibrium. In the forespore sigma F becomes active because transferring the chromosome to the forespore from mother cell takes ~15 mins. So no sigma F is being made at this time so anti-anti sigma degrades anti-sigma leaving sigma F active

Endospore formation restricted to Firmicutes (low GC Gram+) Do all firmicutes produce endospores? Typically how many spores per cell?

Endospores not made by all Firmicutes, probably ancient, lost in some lineages Most well studied in Bacillus subtilis ; core genes conserved, but variations in the process One spore per cell typical but not universal

Comparison of spore types

Endospores: highly resistant; spores completely dormant; for survival (very long term) Streptomyces spores: some resistance; primarily for reproduction and dispersal Myxospores: some resistance; for survival, but not dispersal, cells germinate together in order to hunt as a group

Variations in cell division

Equal cell division: binary fission Unequal cell division: simple budding, budding from hyphae, cell division of stalked organism, polar growth without differentiation of cell size (only one side elongates)

Endospore Structure

Exosporium Protein Coats Cortex (PG, protein) Germ Cell Wall (PG) Inner Forespore Membrane

Compare caulobacter and hyphomicrobium life cycles

For both motile cells do not divide. Flagella falls and sessile (non-motile) mother cells form. Stalk forms. For caulobacter stalk is a holdfast and unequal binary fission occurs. For hyphomicrobium stalk forms and budding occurs from the stalk (hyphae-like)

Epulopiscium genome

Forespore and mother-cell-specific sporulation genes and those for engulfment are conserved. Late sporulation genes for spore coat, resistance and germination not present. Suggests that Epulopiscium lost the ability to form mature spores.

Streptomyces Life Cycle

Germination requires aqueous conditions at the minimum. Spores lose their hydrophobicity Results in water influx and subsequent swelling of the spore. Intracellular trehalose levels decrease as glucose levels increase. Enzymatic activity returns. Germ tube emerges. Branching filaments (substrate mycelia) are non-septate - As the substrate mycelium uses up nutrients, Streptomyces moves into dispersal mode. - Aerial mycelia formation begins spores produced at tips of aerial mycelia Mycelia run out of nutrients, older filaments lyse, releasing nutrients. Antibiotics produced, killing other microbes that may be trying to scavenge nutrients As aerial mycelium matures, spores septate and are dispersed by the wind. Spores not as resistant as endospores and are for reproduction and dispersal

Hyphomicrobium general characteristics

Have polar prosthecae (hyphae) and divide by budding from the tip of the hypha. They have a dimorphic life cycle with a sessile prosthecate mother cell and a motile, nonprosthecate daughter cell.

Streptomyces general characteristics

High GC Gram-Positive Actinobacteria • Common in soil • Most are heterotrophic aerobes with respiratory metabolism • Many produce antibiotics, antiparasitics, anti-cancer agents • Many produce geosmins (fresh dirt smell) • Complex life cycle with a vegetative substrate mycelium and aerial hyphae

what do caulobacter and hyphomicrobium have in common?

Members of the alpha Proteobacteria Oligotrophic bacteria - live in low nutrient aquatic environments. Relatively easy to isolate from nutrient poor soil or water samples Prosthecae/ stalks - extensions of the cell that contain cytoplasm and are bounded by the cell membrane and cell wall - increase the surface area of the cell and the efficiency of nutrient acquisition.

Endospore characteristics

Metabolically inactive, partially dehydrated Very resistant to heat, solvents, desiccation, radiation, acid, peroxide Core contains 10% by weight calcium dipicolinate, contributes to heat resistance Core contains SASPs- small acid soluble spore proteins -bind to DNA, straightening and stiffening it, protect DNA from UV damage, heat, etc. - serve as C and energy source during germination

hyphomicrobium lyfe cycle

Mother cell does not increase in size prior to division. Bud at the tip of the hypha grows, forms a flagellum, septates and swims off to repeat the cycle. Motile daughter cell differentiates into a prosthecate cell by dropping its flagellum, growing a hypha at the opposite pole: the dispersal form.

caulobacter dimorphic life cycle

Motile swarmer cells are chemotactic and are the dispersal form & do not replicate Motile cells- able to sense and locate new sources of nutrients using motility and chemotaxis. The swarmer cell develops into stalked mother cell: - drops flagellum and chemotaxis system components - grows a stalk and a holdfast - replicates DNA & divides. - mother cell can undergo multiple rounds of division

Heliobacterium general characteristics

Photoheterotrophic endospore formers Obligate anaerobes Have unique chlorophyll (g), PSI Fermentative metabolism in dark Found in soil and rice paddies; fixes N2

Desulfotomaculum general characteristics

Rods or curved rods that form endospores Obligately anaerobic sulfate reducers (respire using sulfate as terminal electron acceptor) Autotrophs that use the reductive acetyl-CoA pathway

Caulobacter & Hyphomicrobium similarities and differencens

Similarities: - Dimorphic - Motile swarmer cell- does not replicate - stalks/hyphae are cellular extensions containing cytoplasm, surrounded by cell membrane and cell wall. - mother cell can undergo multiple rounds of replication Differences - budding division vs. unequal binary fission - Hyphomicrobium appendage has a role in reproduction - DNA must pass through hypha of Hyphomicrobium to the bud

caulobacter general characteristics

Small Gram-, straight or curved rods Aerobic organoheterotrophs Cell division is via unequal binary fission. Dimorphic life cycle- has 2 cell forms, sessile and motile.

What predicts a caulobacter stalk length? How strong is a stalk attachment?

The length of the stalk is dependent on the nutrient concentration. longer stalks = larger surface area and better nutrient uptake in dilute environments. Low phosphate levels cause the formation of very long stalks. Phosphate is frequently the most limiting nutrient in aquatic habitats. Essentially a permanent attachment- attempts to remove result in breakage of stalk or at holdfast-stalk interface

Prosthecate/stalked bacteria

Unicellular bacteria with appendages "prosthecae" extending from the cells. Stalks/ prosthecae contain cytoplasm, bounded by the cell membrane and cells wall: increase surface area Complex life cycle w/ unequal cell division & more than one cell type For attachment, floatation and/or increased nutrient uptake

Myxococcus development

Upon starvation, myxobacteria undergo a complex developmental process (aggregate together) to form fruiting bodies that contain resting cells called myxospores. Myxobacteria sporulate together - not for dispersal. Myxospores are resistant to environmental stresses (UV, desiccation), but not as resistant as endospores.

Bacillus thuringiensis (BT) biocontrol application

Useful biological control agent Crystal contains insecticidal proteins called delta endotoxin Toxin is activated at high pH in digestive tract of insect larvae Paralyzes larva digestive system Normally spores of the bacteria, which contain the crystal, are sprayed onto plants. In genetically engineered plants, it provides the plant with resistance to insects.

Epulopiscium reproduction/lyfe cycle

Uses a mechanism very similar to sporulation to reproduce Internal production of multiple live offspring; mother cell lyses (kind of reminds me of viruses) Vegetative cells do not undergo binary fission

Metabacterium polyspora reproduction/lyfe cycle

Vegetative cells rarely undergo binary fission Cells undergo asymmetric division like Bacillus/Clostridium Forespores formed at both poles; can undergo binary fission Vegetative cells form multiple spores as a form of reproduction Spores are released with feces Guinea pigs are coprophagous (eat feces); spores ingested with feces germinate in upper intestine

Myxobacteria general characteristics

members of the delta-Proteobacteria Social bacteria, use intracellular and cell-cell signaling to coordinate the developmental process. Nutrient limitation sensed (C, PO42-, energy, amino acids) Motile by gliding on surfaces - two types of motility: adventurous (A) and social (S) Involves pili and extrusion of polysaccharide slime

Bdellovivrio Predatory life cycle

nonreplicative swimming form attacks and sticks to the outer surface of prey bacteria. Motility & chemotaxis important; pili required. After attachment, Bdellovibrio loses its flagellum, penetrates outer membrane and wall using hydrolytic enzymes (proteases, lipases, lysozyme). Locates in the periplasm The Bdellovibrio converts the host cell to a spherical bdelloplast. Causes the host cell to lose the ability to respire, synthesize RNA, DNA, and proteins and rapidly lose viability. Produces hydrolytic enzymes to degrade host DNA, RNA, proteins, lipids; and assimilates host nucleotides, amino acids, and other cell components to use for C, N, energy etc. Good strategy to keep all the nutrients. Prevents competition. Elongates to form a long helical cell, then divides to form several motile vibrio-shaped daughter cells. The number produced depends on the size of the host cell- typically about 5-6 are produced in E. coli . Additional hydrolytic enzymes are produced to lyse the bdelloplast and allow release of daughter Bdellovibrios Motile cells swim away and can repeat the cycle.

Bdellovibrio general characteristics

obligately predatory bacterium Bdellovibrio (bdello = "leech") Members of the delta subdivision of the Proteobacteria, related to myxobacteria. Widespread in soils, sewage, and fresh- and saltwater environments. Predators of other Gram-negative bacteria, work as individuals. Small (0.25 μm diameter) motile Gram-negative vibrio-shaped bacteria. Obligate aerobes. Motile by single sheathed polar flagellum.

Metabacterium polyspora characteristics

reproduction by multiple endospore formation Endosporeformer in the low G+C Gram positive lineage Inhabits the gastrointestinal tract of guinea pigs Not yet in pure culture Forms multiple endospores as reproductive mechanism

Epulopiscium general characteristics

reproduction by multiple live 'birth' Member of the low G+C Gram positive lineage One of the largest known bacteria >250 μm long Symbiont in the gut of surgeonfish Not yet in pure culture; genome sequence completed