Microbial adaptations and biogeochemical cycling of uranium in polymetallic tailings.

Microorganisms inhabiting uranium (U)-rich environments have specific physiological and biochemical coping mechanisms to deal with U toxicity, and thereby play a crucial role in the U biogeochemical cycling as well as associated heavy metals. We investigated the diversity and functional capabilities of indigenous bacterial communities inhabiting historic U- and Rare-Earth-Elements-rich polymetallic tailings from the Mount Painter Inlier, Northern Flinders Ranges, South Australia. Bacterial diversity profiling identified Actinobacteria as the predominant phylum in all samples. GeoChip analyses revealed the presence of diverse functional genes associated with biogenic element cycling, metal homeostasis/resistance, stress response, and secondary metabolism. The high abundance of metal-resistance and stress-tolerance genes indicates the adaptation of bacterial communities to the "harsh" environmental (metal-rich and semi-arid) conditions of the Northern Flinders Ranges. Additionally, a viable bacterial consortium was enriched from polymetallic tailings. Laboratory experiments demonstrated that the consortium scrubbed uranyl from solution by precipitating a uranyl phosphate biomineral (chernikovite), thus contributing to U biogeochemical cycling. These specialised microbial communities reflect the high specificity of the mineralogy/geochemistry, and biogeography of these U-rich settings. This study provides the fundamental knowledge to develop future applications in securing long-term stability of polymetallic mine waste, and for reprocessing this "waste" to further extract critical minerals.

From biomolecules to biogeochemistry: Exploring the interaction of an indigenous bacterium with gold.

Specialised microbial communities colonise the surface of gold particles in soils/sediments, and catalyse gold dissolution and re-precipitation, thereby contributing to the environmental mobility and toxicity of this 'inert' precious metal. We assessed the proteomic and physiological response of Serratia proteamaculans, the first metabolically active bacterium enriched and isolated directly from natural gold particles, when exposed to toxic levels of soluble Au3+ (10 µM). The results were compared to a metal-free blank, and to cultures exposed to similarly toxic levels of soluble Cu2+ (0.1 mM); Cu was chosen for comparison because it is closely associated with Au in nature due to similar geochemical properties. A total of 273 proteins were detected from the cells that experienced the oxidative effects of soluble Au, of which 139 (51%) were upregulated with either sole expression (31%) or had synthesis levels greater than the Au-free control (20%). The majority (54%) of upregulated proteins were functionally different from up-regulated proteins in the bacteria-copper treatment. These proteins were related to broad functions involving metabolism and biogenesis, followed by cellular process and signalling, indicating significant specificity for Au. This proteomic study revealed that the bacterium upregulates the synthesis of various proteins related to oxidative stress response (e.g., Monothiol-Glutaredoxin, Thiol Peroxidase, etc.) and cellular damage repair, which leads to the formation of metallic gold nanoparticles less toxic than ionic gold. Therefore, indigenous bacteria may mediate the toxicity of Au through two different yet simultaneous processes: i) repairing cellular components by replenishing damaged proteins and ii) neutralising reactive oxygen species (ROS) by up-regulating the synthesis of antioxidants. By connecting the fields of molecular bacteriology and environmental biogeochemistry, this study is the first step towards the development of biotechnologies based on indigenous bacteria applied to gold bio-recovery and bioremediation of contaminated environments.

Association of bacteria in diabetic and non-diabetic foot infection - An investigation in patients from Bangladesh.

The microbial community on a host relies on its immune status and pathophysiological condition. Diabetes mellitus is a metabolic disorder associated with a 25% increased risk of developing foot infection. The pathophysiological differences between diabetic foot infection (DFI) and non-DFI patients may alter the microbial composition in infections. The present study aims to comparatively analyze the microbes colonized in DFI and non-DFI patients in Bangladesh. Pus specimens were collected from 67 DFI and 12 non-DFI patients to investigate the bacteria associated with foot infection. For this investigation, an array of microbiological, molecular biological and immunological approaches were performed. Common bacteria detected in both DFI/non-DFI samples were Pseudomonas spp. (22/29%), Bacillus spp. (12/3%), Enterobacter spp. (22/7%), Staphylococcus spp. (13/13%) and Acinetobacter spp. (10/10%). Enterococcus spp. (9%) and Klebsiella spp. (8%) occurred only in DFI patients, whereas Citrobacter spp. (29%) was only detected in non-DFI samples. The rate of occurrence of three organisms, namely, Enterococcus spp. |Z|=2.2125, Klebsiella spp. |Z|=1.732, Bacillus spp. |Z|=1.9034, were also statistically significant. Most of the isolates from DFI patients were commonly resistant to the cephalosporin (Ceftazidime, Ceftriazone, Cefurozime) and monobactam (Aztreonam) groups of antibiotics. DFI patients had comparatively higher C-reactive protein (CRP) levels than non-DFI patients, and a positive correlation was observed between multi-antibiotic resistance and CRP levels (one of the markers of chronic subclinical inflammation). The present investigation implicated a complex association of the bacterial population in DFI compared with non-DFI with different antimicrobial resistance properties, which was linked with CRP levels.