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#bacterial survival

3 public questions tagged with this topic.

Microbial Physiology

In which growth phase do bacteria prepare for sporulation?

Sporulation is energy expensive differentiation reserved for conditions where vegetative growth cannot continue. Throughout exponential phase nutrients abundant, ribosome content high, cells divide via FtsZ divisome and elongasome MreB. As population density rises and carbon nitrogen phosphate become scarce, quorum peptides ComX CSF and nucleotide second messengers ppGpp c-di-GMP accumulate, sensed by KinA KinB KinC histidine kinases. Kinases activate phosphorelay transferring phosphate from Spo0F to Spo0B to Spo0A master regulator. Phosphorylated Spo0A binds 0A boxes activating over 120 genes initiating asymmetric septation near pole governed by SpoIIE mediated FtsZ relocation. Sigma factor cascade follows compartment specific: SigF in forespore, SigE in mother cell governing engulfment where mother membrane migrates surrounding forespore, then SigG and SigK driving cortex peptidoglycan synthesis, dipicolinic acid calcium complex dehydrating core, and proteinaceous coat crosslinked by transglutaminase. Trigger occurs precisely as cultures enter stationary phase because sufficient ATP and intact chromosomes remain to complete multi-hour morphogenesis before total starvation collapses membrane potential and biosynthetic capacity required for successful spore maturation.

Ref: Prescott's Microbiology, 11th ed., Chapter 7: Bacterial sporulation - Stationary phase Spo0A phosphorelay.

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Microbial Physiology

Bacteria use urease for survival in acidic environments by:

Survival in strongly acidic niches such as stomach lumen colonized by Helicobacter pylori causing gastritis and ulcer disease requires exceptionally efficient neutralization of extreme acidity. Urease is extraordinarily active nickel-dependent metalloenzyme encoded by ureABIEFGH operon containing structural subunits UreA and UreB plus accessory proteins UreE, UreF, UreG, UreD for nickel insertion, hydrolyzing urea abundant in gastric juice and urine into two molecules of ammonia and one carbon dioxide. Ammonia immediately protonates to ammonium NH4+ consuming protons and raising local pH from about 2 to near neutrality, creating protective alkaline cloud that prevents acid denaturation of periplasmic and surface proteins. Carbon dioxide hydrates via carbonic anhydrase to bicarbonate adding second buffering layer. In H. pylori urease represents up to 10 percent total cellular protein. It does not aid protein folding like chaperone nor degrade antibiotics like beta-lactamase nor block glycolysis; its chemical product directly elevates pH and simultaneously provides nitrogen assimilation pathway via glutamine synthetase, underpinning colonization success and pathogenesis.

Ref: Madigan et al., Brock Biology of Microorganisms, 16th ed., Chapter 6: Urease and Acid Survival via Ammonia Production.

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Microbial Physiology

The Thioredoxin system in bacteria is essential for:

Maintenance of intracellular reducing environment and proper thiol-disulfide balance is crucial for protein function, enzyme activity and protection against oxidative damage that would otherwise cause aggregation. The thioredoxin system consists of small 12 kDa redox-active protein thioredoxin TrxA with highly conserved active site motif WCGPC containing two cysteines, flavoprotein thioredoxin reductase TrxB that transfers electrons from NADPH to oxidized thioredoxin via FAD and target disulfide-containing proteins. During oxidative stress or normal oxidative protein maturation in periplasm, inappropriate intermolecular and intramolecular disulfide bonds form in cytoplasmic proteins. Reduced thioredoxin with dithiol performs nucleophilic attack on aberrant disulfide, forming transient mixed disulfide intermediate then resolving through second cysteine to restore native reduced thiols in target and become oxidized itself. TrxB then re-reduces TrxA using NADPH as electron source, completing cycle. This redox cycle also supplies essential electrons to class I ribonucleotide reductase NrdAB for deoxyribonucleotide synthesis required for DNA precursor supply, to methionine sulfoxide reductases MsrA/MsrB that repair oxidized methionine residues, and to peroxiredoxins that detoxify peroxides, explaining essentiality beyond direct antioxidant defense and distinction from activities that inhibit replication or translation.

Ref: Lodish et al., Molecular Cell Biology, 8th ed., Chapter 21: Thioredoxin System and Disulfide Bond Reduction.

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