Profiling bacterial communities associated with sediment-based aquaculture bioremediation systems under contrasting redox regimes

Deposit-feeding invertebrates are proposed bioremediators in microbial-driven sediment-based aquaculture effluent treatment systems. We elucidate the role of the sediment reduction-oxidation (redox) regime in structuring benthic bacterial communities, having direct implications for bioremediation potential and deposit-feeder nutrition. The sea cucumber Holothuria scabra was cultured on sediments under contrasting redox regimes; fully oxygenated (oxic) and redox stratified (oxic-anoxic). Taxonomically, metabolically and functionally distinct bacterial communities developed between the redox treatments with the oxic treatment supporting the greater diversity; redox regime and dissolved oxygen levels were the main environmental drivers. Oxic sediments were colonised by nitrifying bacteria with the potential to remediate nitrogenous wastes. Percolation of oxygenated water prevented the proliferation of anaerobic sulphate-reducing bacteria, which were prevalent in the oxic-anoxic sediments. At the predictive functional level, bacteria within the oxic treatment were enriched with genes associated with xenobiotics metabolism. Oxic sediments showed the greater bioremediation potential; however, the oxic-anoxic sediments supported a greater sea cucumber biomass. Overall, the results indicate that bacterial communities present in fully oxic sediments may enhance the metabolic capacity and bioremediation potential of deposit-feeder microbial systems. This study highlights the benefits of incorporating deposit-feeding invertebrates into effluent treatment systems, particularly when the sediment is oxygenated

Biogeochemical conditions determine virulence of black band disease in corals

The microenvironmental dynamics of the microbial mat of black band disease (BBD) and its less virulent precursor, cyanobacterial patch (CP), were extensively profiled using microsensors under different light intensities with respect to O₂, pH and H₂S. BBD mats exhibited vertical stratification into an upper phototrophic and lower anoxic and sulphidic zone. At the progression front of BBD lesions, high sulphide levels up to 4977 mu M were measured in darkness along with lower than ambient levels of pH (7.43 ± 0.20). At the base of the coral-BBD microbial mat, conditions were hypoxic or anoxic depending on light intensity exposure. In contrast, CP mats did not exhibit strong microchemical stratification with mostly supersaturated oxygen conditions throughout the mats at all light intensities and with levels of pH generally higher than in BBD. Two of three replicate CP mats were devoid of sulphide, while the third replicate showed only low levels of sulphide (up to 42 μM) present in darkness and at intermediate light levels. The level of oxygenation and sulphide correlated well with lesion migration rates, that is virulence of the mats, which were greater in BBD than in CP. The results suggest that biogeochemical microgradients of BBD shaped by the complex microbial community, rather than a defined pathogen, are the major trigger for high virulence and the associated derived coral mortality of this disease

Alteration of Gene Expression, DNA Methylation, and Histone Methylation in Free Radical Scavenging Networks in Adult Mouse Hippocampus following Fetal Alcohol Exposure

<div><p>The molecular basis of Fetal Alcohol Spectrum Disorders (FASD) is poorly understood; however, epigenetic and gene expression changes have been implicated. We have developed a mouse model of FASD characterized by learning and memory impairment and persistent gene expression changes. Epigenetic marks may maintain expression changes over a mouse’s lifetime, an area few have explored. Here, mice were injected with saline or ethanol on postnatal days four and seven. At 70 days of age gene expression microarray, methylated DNA immunoprecipitation microarray, H3K4me3 and H3K27me3 chromatin immunoprecipitation microarray were performed. Following extensive pathway analysis of the affected genes, we identified the top affected gene expression pathway as “Free radical scavenging”. We confirmed six of these changes by droplet digital PCR including the caspase <i>Casp3</i> and Wnt transcription factor <i>Tcf7l2</i>. The top pathway for all methylation-affected genes was “Peroxisome biogenesis”; we confirmed differential DNA methylation in the <i>Acca1</i> thiolase promoter. Altered methylation and gene expression in oxidative stress pathways in the adult hippocampus suggests a novel interface between epigenetic and oxidative stress mechanisms in FASD.</p></div