Mercury Cycling in Sulfur Rich Sediment From The Brunswick Estuary

Mercury is potentially toxic to the environment. Mercury is absorbed into anaerobic sediments of surface waters, which may be converted to methylmercury, a toxic form of mercury that bio-accumulates in aquatic biota. Sources of mercury in the environment vary, but the production of methylmercury is common in sulfur-rich sediments containing mercury. In such environments, sulfur reducing bacteria (SRB) produce methylmercury as a by-product. The metabolic process uses energy from the reduction of sulfate to sulfide. This study focuses on determining the methylmercury production and release potential from sulfur-rich sediments extracted from different areas of the Brunswick Estuary. Previous studies note considerable levels of mercury in the Brunswick Estuary due to a local super fund site. Water and sediment samples were collected from six different sites to feed microcosms. The design measures the potential of the sediments to produce methylmercury. Microcosms were operated under anaerobic conditions to determine if sediments produced methylmercury under extreme conditions (e.g. low dissolved oxygen, low oxidation-reduction potential, and highly productive environment). This may seasonally exist in different zones of the estuary. Results revealed that sediments have the potential to reduce sulfate under anaerobic conditions. In the microcosms, sulfate concentrations rapidly decreased from values as high as 290 mg/L to practically 0 mg/L. This suggests that sediments provide an adequate environment to support SRB activity, which may result in methylmercury production. Further, results revealed that the production potential of methylmercury varies across different zones of the estuary. Precise methylmercury concentrations collected from the different sites are currently being evaluated. Due to the environmental conditions that prevail in the estuary, its proximity to a mercury super fund site, and its accessibility for fishing activities, it is crucial to further assess the methylmercury formation in this area

Robust estimation of bacterial cell count from optical density

Optical density (OD) is widely used to estimate the density of cells in liquid culture, but cannot be compared between instruments without a standardized calibration protocol and is challenging to relate to actual cell count. We address this with an interlaboratory study comparing three simple, low-cost, and highly accessible OD calibration protocols across 244 laboratories, applied to eight strains of constitutive GFP-expressing E. coli. Based on our results, we recommend calibrating OD to estimated cell count using serial dilution of silica microspheres, which produces highly precise calibration (95.5% of residuals <1.2-fold), is easily assessed for quality control, also assesses instrument effective linear range, and can be combined with fluorescence calibration to obtain units of Molecules of Equivalent Fluorescein (MEFL) per cell, allowing direct comparison and data fusion with flow cytometry measurements: in our study, fluorescence per cell measurements showed only a 1.07-fold mean difference between plate reader and flow cytometry data