Abstract Studies have demonstrated that microbes facilitate the incorporation of Mg 2+ into carbonate minerals, leading to the formation of potential dolomite precursors. Most microbes that are capable of mediating Mg-rich carbonates have been isolated from evaporitic environments in which temperature and salinity are higher than those of average marine environments. However, how such physicochemical factors affect and concur with microbial activity influencing mineral precipitation remains poorly constrained. Here, we report the results of laboratory precipitation experiments using two mineral-forming Virgibacillus strains and one non-mineral-forming strain of Bacillus licheniformis , all isolated from the Dohat Faishakh sabkha in Qatar. They were grown under different combinations of temperature (20°, 30°, 40 °C), salinity (3.5, 7.5, 10 NaCl %w/v), and Mg 2+ :Ca 2+ ratios (1:1, 6:1 and 12:1). Our results show that the incorporation of Mg 2+ into the carbonate minerals is significantly affected by all of the three tested factors. With a Mg 2+ :Ca 2+ ratio of 1, no Mg-rich carbonates formed during the experiments. With a Mg 2+ :Ca 2+ ratios of 6 and 12, multivariate analysis indicates that temperature has the highest impact followed by salinity and Mg 2+ :Ca 2+ ratio. The outcome of this study suggests that warm and saline environments are particularly favourable for microbially mediated formation of Mg-rich carbonates and provides new insight for interpreting ancient dolomite formations.
In this research, the interactions of seawater microorganisms with scalants (minerals like calcium sulfate) and antiscalants in the reverse osmosis (RO) systems were investigated. The interaction of seawater microorganisms with antiscalants was investigated by measuring the growth of bacteria in an antiscalant containing growth medium, which was added as a sole source of carbon and energy. Moreover, the interaction of microorganism with calcium sulfate (selected as a model scalant) was also investigated using scanning electron microscopy – energy dispersive x-ray spectroscopic technique. It was found that several Pseudomonas strains isolated from the marine water of Qatar are capable of using antiscalants as an energy or carbon source. It was noted that the growth curves of the strains vary with the type of the antiscalant studied. Furthermore, the results of microorganism-scalant interaction showed that the presence of bacteria induced/mediated precipitation of calcium sulfate on the RO membranes, whereas, no precipitation was noted on the control RO membranes (i.e. without bacteria) under the studied conditions. Therefore, the results of this research showed that the presence of microorganisms in seawater reverse osmosis not only causes biofouling but also enhances mineral scaling through biodegradation of antiscalants and precipitation of minerals (calcium sulfate).
<p>The study of early life on Earth and the search for life on Mars often includes investigations of modern analogues: natural environments that share similarities to what we hypothesize may have existed on the early Earth and early Mars. The study of modern analogues provides key information on how biosignatures are formed and preserved, which is essential for interpreting the geological record. Research conducted in recent years in various modern sabkhas located along the coast of Qatar have demonstrated that these extreme evaporitic environments represent an inspirational gold mine for the field of geobiology and astrobiology.</p><p>The intertidal zones of the Qatari sabkhas are typically colonized by microbial mats. Their presence leads to the formation of Microbially Influenced Sedimentary Structures (MISS). Examples of studied MISS include polygonal, domical, blistered, tufted and crinkled microbial mats. We discuss biological vs. physiochemical factors responsible for their formation, as well as their fossilization potential. These MISS often occur in a precise sequence along a transect from the lower to the upper intertidal zone. We propose that a MISS sequence represents a stronger morphological biosignature than a single MISS. The community composition of some of the studied mats revealed an uppermost layer dominated by anoxygenic phototrophs. We propose that such mats represent a particularly good analogue for studying life in the Early Archean, a time when the cyanobacteria that usually dominate the uppermost photo-oxic layer of most modern mats probably did not exist.</p><p>Besides influencing sediment morphology, the extracellular polymeric substances (EPS) constituting the mats serve as nucleation sites for the precipitation of authigenic minerals. Among these possible precipitates, our research focused on microbially influenced Mg-rich carbonates and Mg-rich silicates. Linking these minerals to a microbial process is of particular interest in view of the forthcoming rover missions to Mars (i.e., ExoMars and Mars 2020). Indeed, orbital spectral analyses revealed the presence of Mg-rich clays and Mg-rich carbonates in the surroundings of the proposed landing sites. It will be exciting to test the hypothesis that, on Mars, some of these minerals may have formed at low temperatures from liquid water and may, therefore, represent a target phase for the investigation of biosignatures.</p>
Water and wastewater are contaminated with various types of trace elements that are released from industrial activities. Their presence, at concentrations above the permissible limit, will cause severe negative impacts on human health and the environment. Due to their cost-effectiveness, simple design, high efficiency, and selectivity, adsorption, and adsorptive filtration are techniques that have received lots of attention as compared to other water treatment techniques. Adsorption isotherms and kinetic studies help to understand the mechanisms of adsorption and adsorption rates, which can be used to develop and optimize different adsorbents. This state-of-the-art review provides and combines the advancements in different conventional and advanced adsorbents, biosorbents, and adsorptive membranes for the removal of trace elements from water streams. Herein, this review discusses the sources of different trace elements and their impact on human health. The review also covers the adsorption technique with a focus on various advanced adsorbents, their adsorption capacities, and adsorption isotherm modeling in detail. In addition, biosorption is critically discussed together with its mechanisms and biosorption isotherms. In the end, the application of various advanced adsorptive membranes is discussed and their comparison with adsorbents and biosorbents is systematically presented.
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