Increased water inputs fuel microbial mercury methylation in upland soils.

Mercury (Hg) can be converted to neurotoxic methylmercury (MeHg) by certain microbes typically in anaerobic environments, threatening human health due to its bioaccumulation in food webs. However, it is unclear whether and how Hg can be methylated in legacy aerobic uplands with increasing water. Here, we conducted a series of incubation experiments to investigate the effects of increased water content on MeHg production in two typical upland soils (i.e., long-term and short-term use). Results showed that marked MeHg production occurred in water-saturated upland soils, which was strongly correlated with the proportions of significantly stimulated Hg methylating taxon (i.e., Geobacter). Elevated temperature further enhanced MeHg production by blooming proportions of typical Hg methylators (i.e., Clostridium, Acetonema, and Geobacter). Water saturation could also enhance microbial Hg methylation by facilitating microbial syntrophy between non-Hg methylators and Hg methylators. Taken together, the present work suggests that uplands could turn into a potential MeHg reservoir in response to water inputs resulting from rainfall or anthropogenic irrigation.

Understanding mercury methylation in the changing environment: Recent advances in assessing microbial methylators and mercury bioavailability.

Methylmercury (MeHg) is a neurotoxin, mainly derived from microbial mercury methylation in natural aquatic environments, and poses threats to human health. Polar regions and paddy soils are potential hotspots of mercury methylation and represent environmental settings that are susceptible to natural and anthropogenic perturbations. The effects of changing environmental conditions on the methylating microorganisms and mercury speciation due to global climate change and farming practices aimed for sustainable agriculture were discussed for polar regions and paddy soils, respectively. To better understand and predict microbial mercury methylation in the changing environment, we synthesized current understanding of how to effectively identify active mercury methylators and assess the bioavailability of different mercury species for methylation. The application of biomarkers based on the hgcAB genes have demonstrated the occurrence of potential mercury methylators, such as sulfate-reducing bacteria, iron-reducing bacteria, methanogen and syntrophs, in a diverse variety of microbial habitats. Advanced techniques, such as enriched stable isotope tracers, whole-cell biosensor and diffusive gradient thin film (DGT) have shown great promises in quantitatively assessing mercury availability to microbial methylators. Improved understanding of the complex structure of microbial communities consisting mercury methylators and non-methylators, chemical speciation of inorganic mercury under geochemically relevant conditions, and the pathway of cellular mercury uptake will undoubtedly facilitate accurate assessment and prediction of in situ microbial mercury methylation.

[Analysis of full-length gene sequence of a rabies vaccine strain CTN-1 for human use in China].

CTN-1 is one of the rabies vaccine strains for human use in China, but there has been no report on the full-length gene sequence of CTN-1. In this study, the full-length gene of CTN-1 was amplified by RT-PCR, each PCR product was cloned into T vector and then sequenced, assemblied and compared with other vaccine strains as well as the wild Chinese rabies isolates. The phylogenetic tree of G gene was constructed and the genetic homology was analyzed. The results revealed that CTN-1 was 11 925nt (GenBank accession number: FJ959397)in length and belonged to the genotype I. The full-length nucleotide homologies among CTN-1 and other rabies virus strains were between 81.5%-93.4%, of which the lowest 81.5% was between CTN-1 strain and bat isolate SHBRV, and the highest 93.4% was between CTN-1 and Chinese isolate HN10. The phylogenetic analysis revealed that the majority of Chinese isolates could be grouped into the same clade with the CTN-1 strain, but aG and some vaccine strains from abroad such as Flury, PM, PV, ERA, RC-HL and a few Chinese strains were grouped in another clade. Comparsion of the G protein genes also showed that the homologies among CTN-1 and most of the Chinese isolates were higher than that of the other vaccine strains to those Chinese strains. Therefore, it suggests that the CTN-1 strain is more suitable and rational to be used for the production of rabies inactivated vaccine in China than the others.