Seasonal Change of Sediment Microbial Communities and Methane Emission in Young and Old Mangrove Forests in Xuan Thuy National Park.

Microbial communities in mangrove forests have recently been intensively investigated to explain the ecosystem function of mangroves. In this study, the soil microbial communities under young (<11 years-old) and old (>17 years-old) mangroves have been studied during dry and wet seasons. In addition, biogeochemical properties of sediments and methane emission from the two different mangrove ages were measured. The results showed that young and old mangrove soil microbial communities were significantly different on both seasons. Seasons seem to affect microbial communities more than the mangrove age does. Proteobacteria and Chloroflexi were two top abundant phyla showing >15%. Physio-chemical properties of sediment samples showed no significant difference between mangrove ages, seasons, nor depth levels, except for TOC showing significant difference between the two seasons. The methane emission rates from the mangroves varied depending on seasons and ages of the mangrove. However, this did not show significant correlation with the microbial community shifts, suggesting that abundance of methanogens was not the driving factor for mangrove soil microbial communities.

Copper Tolerance of Novel Rhodotorula sp. Yeast Isolated from Gold Mining Ore in Gia Lai, Vietnam.

In this study, twenty-five yeast strains were isolated from soil samples collected in the gold mining ore in Gia Lai, Vietnam. Among them, one isolate named GL1T could highly tolerate Cu2+ up to 10 mM, and the isolates could also grow in a wide range of pH (3-7), and temperature (10-40 °C). Dried biomass of GL1 was able to remove Cu2+ effectively up to 90.49% with a maximal biosorption capacity of 18.1 mg/g at pH 6, temperature 30 °C, and incubation time 60 min. Sequence analysis of rDNA indicated this strain was closely related to Rhodotorula mucilaginosa but with 1.53 and 3.46% nucleotide differences in the D1/D2 domain of the 28S rRNA gene and the ITS1-5.8S rRNA gene-ITS2 region sequence, respectively. Based on phylogenetic tree analysis and the biochemical characteristics, the strain appears to be a novel Rhodotorula species, and the name Rhodotorula aurum sp. nov. is proposed. This study provides us with more information about heavy metal-tolerant yeasts and it may produce a new tool for environmental control and metal recovery operations.

Antibacterial effect of copper nanoparticles produced in a Shewanella-supported non-external circuit bioelectrical system on bacterial plant pathogens.

The use of copper nanoparticles for the inhibition of plant pathogens Ralstonia solanacearum, which causes wilt disease, and Xanthomonas axonopodis, which causes citrus canker, was investigated in this study. To avoid the inhibiting effect of Cu2+ ions on the bacterial cells, the copper nanoparticles were synthesized in the cathode chamber of a non-external circuit bioelectrochemical system (nec_BES) inoculated with Shewanella sp. HN-41 at the anode. The electrons produced by the oxidation of lactate by Shewanella sp. HN-41 were directly transferred to the anolyte in the cathode via a graphite electrode connecting the anode and cathode chambers. SEM images of the produced particles revealed that the copper nanoparticles were aggregated into spherical shapes with an average size of 2.9 µm from smaller particles with a size range from 30 nm to approximately 190 nm. X-ray diffraction demonstrated that the copper nanoparticles were mainly in the form of a single-phase crystal mixture of atacamite (Cu2Cl(OH)3) and paracatamite (Cu2Cl(OH)3). Finally, for the application of synthesized nanoparticles, an agar diffusion test was applied to assess the antibacterial activity of the formed copper nanoparticles in propylene glycol solvent against R. solanacearum and X. axonopodis. The results showed that the nanoparticles damaged the cells of R. solanacearum, with a half maximum inhibition (IC50) value of 42 ppm, but did not damage X. axonopodis cells.

Complete Genome Sequence of Shigella sonnei Strain SE6-1, Capable of Selenate Reduction.

We report the complete genome sequence of selenate [Se(VI)]-reducing Shigella sonnei SE6-1, which was isolated from stream sediment from an industrial complex in Jeonju, South Korea. The genome sequence is 4,762,774 bp long, with a G+C content of 50.7% and 4,548 genes, including 4,440 coding sequences, 22 rRNA genes, and 86 tRNA genes.

Impact of anthropogenic activities on water quality and plankton communities in the Day River (Red River Delta, Vietnam).

Planktons are a major component of food web structure in aquatic ecosystems. Their distribution and community structure are driven by the combination and interactions between physical, chemical, and biological factors within the environment. In the present study, water quality and the community structure of phytoplankton and zooplankton were monthly investigated from January to December 2015 at 11 sampling sites along the gradient course of the Day River (Red River Delta, northern Vietnam). The study demonstrated that the Day River was eutrophic with the average values of total phosphorus concentration 0.17 mg/L, total nitrogen concentration 1.98 mg/L, and Chl a 54 µg/L. Microscopic plankton analysis showed that phytoplankton comprised 87 species belonging to seven groups in which Chlorophyceae, Bacillariophyceae, and Cyanobacteria accounted for the most important constituents of the river's phytoplankton assemblage. A total 53 zooplankton species belonging to three main groups including Copepoda, Cladocera, and Rotatoria were identified. Plankton biomass values were greatest in rainy season (3002.10-3 cell/L for phytoplankton and 12.573 individuals/m3 for zooplankton). Using principal correspondence and Pearson correlation analyses, it was found that the Day River was divided into three main site groups based on water quality and characteristics of plankton community. Temperature and nutrients (total phosphorus and total nitrogen) are key factors regulating plankton abundance and distribution in the Day River.

Mercury capture into biogenic amorphous selenium nanospheres produced by mercury resistant Shewanella putrefaciens 200.

Shewanella putrefaciens 200, resistant to high concentration of Hg(II), was selected for co-removal of mercury and selenium from aqueous medium. Biogenic Hg(0) reduced from Hg(II) by S. putrefaciens 200 was captured into extracellular amorphous selenium nanospheres, resulting in the formation of stable HgSe nanoparticles. This bacterial reduction could be a new strategy for mercury removal from aquatic environments without secondary pollution of mercury methylation or Hg(0) volatilization.

Growth mechanism of amorphous selenium nanoparticles synthesized by Shewanella sp. HN-41.

Shewanella sp. HN-41 was exploited for selenium nanoparticles synthesis from aqueous selenite compounds under anaerobic conditions. Various reaction conditions, including reaction time, initial biomass, and initial selenite concentration, were systematically investigated to determine their effects on particle size distribution and formation rate. The biomass concentration of Shewanella sp. HN-41 had no significant effect on average particle size but strongly influenced reduction rate and size distribution. Initial selenite concentration (0.01-1.0 mM) also had no significant effect on the average particle size, but affected the early growth stage mechanism of selenium particle production, which was modeled using a Michaelis Menten model. The HR-TEM and SAED patterns indicated that the synthesized selenium nanoparticles were amorphous.