Increase of Salt Tolerance in Carbon-Starved Cells of Rhodopseudomonas palustris Depending on Photosynthesis or Respiration

Mechanism on the microbial salt tolerance enhancement by electrical stimulation

The application of biological methods in industrial saline wastewater treatment is limited, since the activities of microorganisms are strongly inhibited by the highly concentrated salts. Acclimatized halotolerant and halophilic microorganisms are of high importance since they can resist the environmental stresses of high salinity. The acclimation to salinity can be passive or active based on whether external simulation is used. However, there is a need for development of economic, efficient and reliable active biological stimulation technologies to accelerate salinity acclimation. Recent studies have shown that electrical stimulation can effectively enhance microbial salt tolerance and pollutant removal ability. However, there have been no comprehensive reviews of the mechanisms involved. Therefore, this mini-review described the mechanisms of electrical stimulation that can significantly improve microbial bioactivity and biodiversity. These mechanisms include regulation of Na⁺ and K⁺ transporters by changing membranepotential and promoting ATP production, as well as regulation of extracellular polymer substances through enhanced release of low molecular weight EPS and quorum sensing molecules. The information provided herein will facilitate the application of biological high-salinity wastewater treatment.

Bioelectrochemical systems for environmental remediation of estrogens: A review and way forward

Globally estrogenic pollutants are a cause of concern in wastewaters and water bodies because of their high endocrine disrupting activity leading to extremely negative impacts on humans and other organisms even at very low environmental concentrations. Bioremediation of estrogens has been studied extensively and one technology that has emerged with its promising capabilities is Bioelectrochemical Systems (BESs). Several studies in the past have investigated BESs applications for treatment of wastewaters containing toxic recalcitrant pollutants with a primary focus on improvement of performance of these systems for their deployment in real field applications. But the information is scattered and further the improvements are difficult to achieve for standalone BESs. This review critically examines the various existing treatment technologies for the effective estrogen degradation. The major focus of this paper is on the technological advancements for scaling up of these BESs for the real field applications along with their integration with the existing and conventional wastewater treatment systems. A detailed discussion on few selected microbial species having the unusual properties of heterotrophic nitrification and extraordinary stress response ability to toxic compounds and their degradation has been highlighted. Based on the in-depth study and analysis of BESs, microbes and possible benefits of various treatment methods for estrogen removal, we have proposed a sustainable Hybrid BES-centered treatment system for this purpose as a choice for wastewater treatment. We have also identified three pipeline tasks that reflect the vital parts of the life cycle of drugs and integrated treatment unit, as a way forward to foster bioeconomy along with an approach for sustainable wastewater treatment.

iTRAQ-based quantitative proteomics reveals insights into metabolic and molecular responses of glucose-grown cells of Rubrivivax benzoatilyticus JA2

Anoxygenic photosynthetic bacteria thrive under diverse habitats utilising an extended range of inorganic/organic compounds under different growth modes. Although they display incredible metabolic flexibility, their responses and adaptations to changing carbon regimes is largely unexplored. In the present study, we employed iTRAQ-based global proteomic profiling and physiological studies to uncover the adaptive strategies of a phototrophic bacterium, Rubrivivax benzoatilyticus JA2 to glucose. Strain JA2 displayed altered growth rates, reduced cell size and progressive loss of pigmentation when grown on glucose compared to malate under photoheterotrophic condition. A ten-fold increase in the saturated to unsaturated fatty acid ratio of glucose-grown cells indicates a possible membrane adaptation. Proteomic profiling revealed extensive metabolic remodelling in the glucose-grown cells wherein signal-transduction, selective-transcription, DNA-repair, transport and protein quality control processes were up-regulated to cope with the changing milieu. Proteins involved in DNA replication, translation, electron-transport, photosynthetic machinery were down-regulated possibly to conserve the energy. Glycolysis/gluconeogenesis, TCA cycle and pigment biosynthesis were also down-regulated. The cell has activated alternative energy metabolic pathways viz., fatty acid β-oxidation, glyoxylate, acetate-switch and Entner-Doudoroff pathways. Overall, the present study deciphered the molecular/metabolic events associated with glucose-grown cells of strain JA2 and also unraveled how a carbon source modulates the metabolic phenotypes. SIGNIFICANCE: Anoxygenic photosynthetic bacteria (APB) exhibit incredible metabolic flexibility leading to diverse phenotypes. They thrive under diverse habitat using an array of inorganic/organic compounds as carbon sources, yet their metabolic adaptation to varying carbon regime is mostly unexplored. Present study uncovered the proteomic insights of the cellular responses of strain JA2 to changing carbon sources viz. malate and glucose under photoheterotrophic conditions. Our study suggests that carbon source can also determine the metabolic fate of the cells and reshape the energy dynamics of APB. Here, for the first time study highlighted the plausible carbon source (glucose) mediated regulation of photosynthesis in APB. The study sheds light on the plausible cellular events and adaptive metabolic strategies employed by strain JA2 in presence of non-preferred carbon source. It also revealed new insights into the metabolic plasticity of APB to the changing milieu.