Bioenergetics of the Moderately Halophilic Bacterium Halobacillus halophilus: Composition and Regulation of the Respiratory Chain

Abstract

In their natural environments, moderately halophilic bacteria are confronted not only with high salinities but also with low oxygen tensions due to the high salinities. The growth of H. halophilus is strictly aerobic. To analyze the dependence of respiration on the NaCl concentration and oxygen availability of the medium, resting cell experiments were performed. The respiration rates were dependent on the NaCl concentration of the growth medium, as well as on the NaCl concentration of the assay buffer, indicating regulation on the transcriptional and the activity level. Respiration was accompanied by the generation of an electrochemical proton potential (⌬ H ؉) across the cytoplasmic membrane whose magnitude was dependent on the external pH. Genes encoding proteins involved in respiration and ⌬ H ؉ generation, such as a noncoupled NADH dehydrogenase (NDH-2), complex II, and complex III, were identified in the genome. In addition, genes encoding five different terminal oxidases are present. Inhibitor profiling revealed the presence of NDH-2 and complex III, but the nature of the oxidases could not be resolved using this approach. Expression analysis demonstrated that all the different terminal oxidases were indeed expressed, but by far the most prominent was cta, encoding cytochrome caa 3 oxidase. The expression of all of the different oxidase genes increased at high NaCl concentrations, and the transcript levels of cta and qox (encoding cytochrome aa 3 oxidase) also increased at low oxygen concentrations. These data culminate in a model of the composition and variation of the respiratory chain of H. halophilus.

Biodesalination—On harnessing the potential of nature’s desalination processes

“…They also use the H + gradient to expel Na + from the cell. The generalized transport reaction catalyzed by Na + /H + antiporters is: Na + (in) + 2 H + (out)  Na + (out) + 2 H + (in) [27].…”

CeO2 Nanoparticles Regulate the Propagation of Antibiotic Resistance Genes by Altering Cellular Contact and Plasmid Transfer

“…In addition, ATP plays an important role in the conjugation, providing energy for building conjugative transfer apparatus, replicating plasmids and the transport across cell membranes . Considering the electron extraction for the reduction of Ce 4+ to Ce 3+ , the electron transport chain (ETC) for cellular energy production is hypothesized to be susceptible to CeO 2 NPs.…”

“…In addition, ATP plays an important role in the conjugation, providing energy for building conjugative transfer apparatus, replicating plasmids and the transport across cell membranes. 17 Considering the electron extraction for the reduction of Ce 4+ to Ce 3+ , 16 the electron transport chain (ETC) for cellular energy production 18 Generally, plant growth can be significantly promoted in soil or water spiked with CeO 2 nanomaterials at concentrations lower than 100 ppm; 19 however, the effects of these CeO 2 NPs on the ARGs transfer in agricultural soils remain unknown. To minimize the introduction of CeO 2 NPs into the environment and to reduce the cost for practical applications, 50 mg/kg was set as the maximum in this study.…”