Growth of Bacillus subtilis cells, normally adapted at Earth-normal atmospheric pressure (ϳ101.3 kPa), was progressively inhibited by lowering of pressure in liquid LB medium until growth essentially ceased at 2.5 kPa. Growth inhibition was immediately reversible upon return to 101.3 kPa, albeit at a slower rate. A population of B. subtilis cells was cultivated at the near-inhibitory pressure of 5 kPa for 1,000 generations, where a stepwise increase in growth was observed, as measured by the turbidity of 24-h cultures. An isolate from the 1,000-generation population was obtained that showed an increase in fitness at 5 kPa when compared to the ancestral strain or a strain obtained from a parallel population that evolved for 1,000 generations at 101.3 kPa. The results from this preliminary study have implications for understanding the ability of terrestrial microbes to grow in low-pressure environments such as Mars.Microorganisms grow optimally within a characteristic range of fundamental physical parameters such as temperature, osmolarity, pH, and pressure. Cells that can grow at the extreme limits of these parameters are known collectively as extremophiles (reviewed in reference 8). Thus, in extreme environments on Earth there exist halophiles in hypersaline niches, psychrophiles and thermophiles in extreme cold and hot environments, and acidophiles or alkaliphiles in environments of extreme acidic or basic pH. Regarding extremes of pressure, piezophiles (barophiles) have been isolated from high-pressure (hyperbaric) submarine environments and have been studied rather extensively; in addition, high pressure has been shown to exert lethal and inhibitory effects on various microbial systems not normally adapted to high pressure (reviewed in reference 19). On the opposite extreme, there has been very little investigation concerning the survival and growth of microbes under conditions of extremely low atmospheric pressure (hypobaria), primarily because such environments do not exist in nature on the Earth's surface. However, some investigators in the emerging field of astrobiology have become concerned with microbial survival and/or growth at low pressures because (i) the closest potential life-bearing planet, Mars, contains a low-pressure atmosphere, and (ii) the possibility exists that terrestrial microbes could be transferred from Earth to Mars as a result of natural impacts (23) or human spaceflight activities (24). Most of the experiments conducted have concentrated on testing the ability of terrestrial microbes merely to survive in the Mars surface environment (reviewed in references 6, 23, and 28); relatively few experiments have tested the ability of specific Earth microbes to grow or metabolize at reduced pressure (12,14). We previously reported that growth of at least 37 different microorganisms on semisolid agar medium was inhibited at pressures approaching ϳ2.5 to 3.5 kPa (3,4,27,30). (Note that atmospheric pressures at the surfaces of Earth and Mars average ϳ101.3 kPa and ϳ0.7 kPa, respectively [26].) T...

The role played by the Y-family DNA polymerases YqjH and YqjW in protecting sporulating cells of Bacillus subtilis from DNA damage was determined. The absence of either yqjH and/or yqjW not only reduced sporulation efficiency but also sensitized the sporulating cells to hydrogen peroxide, tert-butylhydroperoxide (t-BHP), mitomycin-C (M-C), and UV-C radiation. Moreover, these DNA-damaging agents increased the mutation frequency of wild-type sporulating cells to 4-azaleucine, but the production of mutants was YqjH- and YqjW-dependent. In conclusion, the results presented here indicate that YqjH/YqjW-dependent-translesion synthesis (TLS) operates in sporulating B. subtilis cells and contributes in processing spontaneous and artificially induced genetic damage, which is apparently required for an efficient sporulation process.

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Microbacterium liquefaciens MNSH2-PHGII-2 is a nickel-vanadium-resistant bacterium isolated from mine tailings located in Guanajuato, Mexico. In PHGII liquid media, M. liquefaciens has the ability to remove 29.5 ppm of Ni and 168.3 ppm of V. The present study reports, for the first time in M. liquefaciens, the presence of the genes nccA (Ni-Co-Cd resistance), hant (high-affinity nickel transporter), smtA, a metal-binding protein gene, and VAN2 (V resistance), which showed an increased expression under exposure to 200 ppm of Ni and 200 ppm of V during the logarithmic growth phase of the microorganism in PHGII liquid media. Data about the expression profile of genes conferring metal resistance to M. liquefaciens can improve the knowledge of those mechanisms involved in the processes of Ni-V resistance and probably in Ni-V removal processes. Based on our data, we can suggest that M. liquefaciens has the potential to be used in the biological treatment of toxic wastes with high Ni and V content.