Prospects for harnessing biocide resistance for bioremediation and detoxification

Microorganisms that have a pH optimum for growth of less than pH 3 are termed "acidophiles". To grow at low pH, acidophiles must maintain a pH gradient of several pH units across the cellular membrane while producing ATP by the influx of protons through the F(0)F(1) ATPase. Recent advances in the biochemical analysis of acidophiles coupled to sequencing of several genomes have shed new insights into acidophile pH homeostatic mechanisms. Acidophiles seem to share distinctive structural and functional characteristics including a reversed membrane potential, highly impermeable cell membranes and a predominance of secondary transporters. Also, once protons enter the cytoplasm, methods are required to alleviate effects of a lowered internal pH. This review highlights recent insights regarding how acidophiles are able to survive and grow in these extreme conditions.

Life at high salt concentrations is energetically expensive. The upper salt concentration limit at which different dissimilatory processes occur in nature appears to be determined to a large extent by bioenergetic constraints. The main factors that determine whether a certain type of microorganism can make a living at high salt are the amount of energy generated during its dissimilatory metabolism and the mode of osmotic adaptation used. I here review new data, both from field observations and from the characterization of cultures of new types of prokaryotes growing at high salt concentrations, to evaluate to what extent the theories formulated 12 years ago are still valid, need to be refined, or should be refuted on the basis of the novel information collected. Most data agree well with the earlier theories. Some new observations, however, are not easily explained: the properties of Natranaerobius and other haloalkaliphilic thermophilic fermentative anaerobes, growth of the sulfate-reducing Desulfosalsimonas propionicica with complete oxidation of propionate and Desulfovermiculus halophilus with complete oxidation of butyrate, growth of lactate-oxidizing sulfate reducers related to Desulfonatronovibrio at 346 g l(-1) salts at pH 9.8, and occurrence of methane oxidation in the anaerobic layers of Big Soda Lake and Mono Lake. © 2010 Society for Applied Microbiology and Blackwell Publishing Ltd.

Among the adaptive responses of bacteria to rapid changes in environmental conditions, those of the cell envelope are known to be the most crucial. Therefore, several mechanisms with which bacteria change their cell surface and membranes in the presence of different environmental stresses have been elucidated. Among these mechanisms, the release of outer membrane vesicles (MV) in Gram-negative bacteria has attracted particular research interest because of its involvement in pathogenic processes, such as that of Pseudomonas aeruginosa biofilm formation in cystic fibrosis lungs. In this study, we investigated the role of MV formation as an adaptive response of Pseudomonas putida DOT-T1E to several environmental stress factors and correlated it to the formation of biofilms. In the presence of toxic concentrations of long-chain alcohols, under osmotic stress caused by NaCl, in the presence of EDTA, and after heat shock, cells of this strain released MV within 10 min in the presence of a stressor. The MV formed showed similar size and charge properties, as well as comparable compositions of proteins and fatty acids. MV release caused a significant increase in cell surface hydrophobicity, and an enhanced tendency to form biofilms was demonstrated in this study. Therefore, the release of MV as a stress response could be put in a physiological context.