Utilizing biochars to stabilize mercury in contaminated floodplain sediment: Implications on mercury remediation.

Major weather events contribute to the mobility and remobilization of legacy mercury (Hg) contamination and sequestration within sediments. Remediation using biochar as a soil amendment is a useful technique to immobilize and decrease Hg toxicity. This study explored whether biochar application is effective at stabilizing labile mercury (LaHg) from floodplain sediment. Controlled mesocosms simulating contamination events and flooding conditions were conducted. Floodplain sediment, which experiences annual periodic flooding, was collected. Sediment was spiked with inorganic Hg, applied with different types of biochar, and experienced simulated flooding events. Four types of biochar, pure rice husk (RH), pure peanut hull (PH), sulfur-modified rice husk (SMRH), and sulfur-modified peanut hull (SMPH), were applied at 10 and 40 g/kg rates (i.e., RH 10, RH 40; PH 10, PH 40, SMRH 10, SMRH 40, SMPH 10, SMPH 40). Total Hg, methylmercury, and LaHg concentrations were analyzed by coupling with redox potential measurements. Results indicate that SMRH 10, PH 10, PH 40, SMPH 10, and SMPH 40 successfully remediate Hg by stabilizing and reducing LaHg species from floodplain sediment. However, a high Hg methylation potential was observed with unsulfated and sulfated peanut hulls (PH 10, PH 40, SMPH 10, and SMPH 40), as they tend to create a reducing microenvironment that favors sulfate reduction reactions. Additionally, sulfur-modified biochar tends to promote Hg methylation potential at high application rates (i.e., 40 g/kg). We thus recommend using SMRH at a relatively low application rate (SMRH 10) for the remediation of Hg from floodplain sediment.

The Microbiota of Freshwater Fish and Freshwater Niches Contain Omega-3 Fatty Acid-Producing Shewanella Species.

Approximately 30 years ago, it was discovered that free-living bacteria isolated from cold ocean depths could produce polyunsaturated fatty acids (PUFA) such as eicosapentaenoic acid (EPA) (20:5n-3) or docosahexaenoic acid (DHA) (22:6n-3), two PUFA essential for human health. Numerous laboratories have also discovered that EPA- and/or DHA-producing bacteria, many of them members of the Shewanella genus, could be isolated from the intestinal tracts of omega-3 fatty acid-rich marine fish. If bacteria contribute omega-3 fatty acids to the host fish in general or if they assist some bacterial species in adaptation to cold, then cold freshwater fish or habitats should also harbor these producers. Thus, we undertook a study to see if these niches also contained omega-3 fatty acid producers. We were successful in isolating and characterizing unique EPA-producing strains of Shewanella from three strictly freshwater native fish species, i.e., lake whitefish (Coregonus clupeaformis), lean lake trout (Salvelinus namaycush), and walleye (Sander vitreus), and from two other freshwater nonnative fish, i.e., coho salmon (Oncorhynchus kisutch) and seeforellen brown trout (Salmo trutta). We were also able to isolate four unique free-living strains of EPA-producing Shewanella from freshwater habitats. Phylogenetic and phenotypic analyses suggest that one producer is clearly a member of the Shewanella morhuae species and another is sister to members of the marine PUFA-producing Shewanella baltica species. However, the remaining isolates have more ambiguous relationships, sharing a common ancestor with non-PUFA-producing Shewanella putrefaciens isolates rather than marine S. baltica isolates despite having a phenotype more consistent with S. baltica strains.

Single rapamycin administration induces prolonged downward shift in defended body weight in rats.

Manipulation of body weight set point may be an effective weight loss and maintenance strategy as the homeostatic mechanism governing energy balance remains intact even in obese conditions and counters the effort to lose weight. However, how the set point is determined is not well understood. We show that a single injection of rapamycin (RAP), an mTOR inhibitor, is sufficient to shift the set point in rats. Intraperitoneal RAP decreased food intake and daily weight gain for several days, but surprisingly, there was also a long-term reduction in body weight which lasted at least 10 weeks without additional RAP injection. These effects were not due to malaise or glucose intolerance. Two RAP administrations with a two-week interval had additive effects on body weight without desensitization and significantly reduced the white adipose tissue weight. When challenged with food deprivation, vehicle and RAP-treated rats responded with rebound hyperphagia, suggesting that RAP was not inhibiting compensatory responses to weight loss. Instead, RAP animals defended a lower body weight achieved after RAP treatment. Decreased food intake and body weight were also seen with intracerebroventricular injection of RAP, indicating that the RAP effect is at least partially mediated by the brain. In summary, we found a novel effect of RAP that maintains lower body weight by shifting the set point long-term. Thus, RAP and related compounds may be unique tools to investigate the mechanisms by which the defended level of body weight is determined; such compounds may also be used to complement weight loss strategy.