Conditional spore cortex-less mutants of Bacillus sphaericus 9602

New Thoughts on an Old Topic: Secrets of Bacterial Spore Resistance Slowly Being Revealed

The quest for bacterial survival is exemplified by spores formed by some Firmicutes members. They turn up everywhere one looks, and their ubiquity reflects adaptations to the stresses bacteria face. Spores are impactful in public health, food safety, and biowarfare. Heat resistance is the hallmark of spores and is countered principally by a mineralized gel-like protoplast, termed the spore core, with reduced water which minimizes macromolecular movement/denaturation/aggregation. Dry heat, however, introduces mutations into spore DNA. Spores have countermeasures to extreme conditions that are multifactorial, but the fact that spore DNA is in a crystalline-like nucleoid in the spore core, likely due to DNA saturation with small acid-soluble spore proteins (SASPs), suggests that reduced macromolecular motion is also critical in spore dry heat resistance. SASPs are also central in the radiation resistance characteristic of spores, where the contributions of four spore features-SASP; Ca2+, with pyridine-2,6-dicarboxylic acid (CaDPA); photoproduct lyase; and low water content-minimize DNA damage. Notably, the spore environment steers UV photochemistry toward a product that germinated spores can repair without significant mutagenesis. This resistance extends to chemicals and macromolecules that could damage spores. Macromolecules are excluded by the spore coat which impedes the passage of moieties of ≥10 kDa. Additionally, damaging chemicals may be degraded or neutralized by coat enzymes/proteins. However, the principal protective mechanism here is the inner membrane, a compressed structure lacking lipid fluidity and presenting a barrier to the diffusion of chemicals into the spore core; SASP saturation of DNA also protects against genotoxic chemicals. Spores are also resistant to other stresses, including high pressure and abrasion. Regardless, overarching mechanisms associated with resistance seem to revolve around reduced molecular motion, a fine balance between rigidity and flexibility, and perhaps efficient repair.

Specific inhibition of the Na(+)-driven flagellar motors of alkalophilic Bacillus strains by the amiloride analog phenamil

Amiloride, a specific inhibitor for the Na(+)-driven flagellar motors of alkalophilic Bacillus strains, was found to cause growth inhibition; therefore, the use of amiloride for the isolation of motility mutants was difficult. On the other hand, phenamil, an amiloride analog, inhibited motor rotation without affecting cell growth. A concentration of 50 microM phenamil completely inhibited the motility of strain RA-1 but showed no effect on the membrane potential, the intracellular pH, or Na(+)-coupled amino acid transport, which was consistent with the fact that there was no effect on cell growth. Kinetic analysis of the inhibition of motility by phenamil indicated that the inhibition was noncompetitive with Na+ in the medium. A motility mutant was isolated as a swarmer on a swarm agar plate containing 50 microM phenamil. The motility of the mutant showed an increased resistance to phenamil but normal sensitivity to amiloride. These results suggest that phenamil and amiloride interact at different sites on the motor. By examining various bacterial species, phenamil was found to be a specific and potent inhibitor for the Na(+)-driven flaggellar motors not only in various strains of alkalophilic Bacillus spp. but also in a marine Vibrio sp.

Red pigment in Bacillus megaterium spores

Bacillus megaterium QM B1551 spores contained a unique red pigment in their membranes that was not found in other species. This red pigment, presumably a carotenoid, was synthesized about the time of dipicolinic acid synthesis during sporulation and was associated with the forespores. A yellow pigment was synthesized during sporulation in rich medium and was found in the mother cell compartment. Although the yellow pigment was also associated with spores, it could be removed by two different extraction procedures without impairing germination; it was absent when sporulation occurred in a minimal medium. Although the yellow pigment of the mother cell appeared to be dispensable, the red pigment may serve a more critical function, such as membrane stabilization.

Electron microscope studies of conditional spore cortexless mutants of Bacillus sphaericus

Spore cortex of conditional cortexless mutants of Bacillus sphaericus 9602 was not detectable by electron microscopy unless the medium was supplemented with meso-alpha,epsilon-diaminopimelic acid during sporulation. Other spore structures appeared normal. Spore shape was quite irregular in the absence of meso-alpha,epsilon-diaminopimelic acid.