Two selenium tolerant Lysinibacillus sp. strains are capable of reducing selenite to elemental Se efficiently under aerobic conditions

Microbes play important roles in the transport and transformation of selenium(Se) in the environment, thereby influencing plant resistance to Se and Se accumulation in plant. The objectives are to characterize the bacteria with high Se tolerance and reduction capacity and explore the significance of microbial origins on their Se tolerance, reduction rate and efficiency. Two bacterial strains were isolated from a naturally occurred Se-rich soil at tea orchard in southern Anhui Province, China. The reduction kinetics of selenite was investigated and the reducing product was characterized using scanning electron microscopy and transmission electron microscopy-energy dispersive spectroscopy. The bacteria were identified as Lysinibacillus xylanilyticus and Lysinibacillus macrolides,respectively, using morphological, physiological and molecular methods. The results showed that the minimal inhibitory concentrations(MICs) of selenite for L. xylanilyticus and L. macrolides were 120 and 220 mmol/L, respectively, while MICs of selenate for L.xylanilyticus and L. macrolides were 800 and 700 mmol/L, respectively. Both strains aerobically reduced selenite with an initial concentration of 1.0 mmol/L to elemental Se nanoparticles(SeNPs) completely within 36 hr. Biogenic SeNPs were observed both inside and outside the cells suggesting either an intra-or extracellular reduction process. Our study implied that the microbes from Se-rich environments were more tolerant to Se and generally quicker and more efficient than those from Se-free habitats in the reduction of Se oxyanions. The bacterial strains with high Se reduction capacity and the biological synthesized Se NPs would have potential applications in agriculture, food, environment and medicine.

Plant species coexistence alleviates the impacts of lead on Zea mays L.

Whether plant coexistence can reduce the impacts of lead (Pb) on crops in agroecosystems has not been well understood. We conducted a factorial experiment to investigate the effects of weeds coexisting with maize (Zea mays L.) on Pb accumulation in maize and soil microbes at two Pb levels (ambient and 300 mg/kg). Elevated Pb tended to increase the Pb concentration in maize and decreased soil microbial activity (indicated by the average well color development, AWCD), functional group diversity, as well as arbuscular mycorrhizal (AM) colonization and vesicle number of maize. Compared to the monoculture, weeds coexisting with maize reduced the Pb concentrations in the root, leaf, sheath and stem of maize at both seedling and mature stages. In maize-weed mixtures, soil microbial activity and functional group diversity tended to increase for both Pb treatments relative to the monoculture. Furthermore, principal component analysis revealed that the soil microbial community structure changed with the introduction of weeds. The highest Pb accumulation in weeds occurred for the elevated Pb treatment in a three species mixture. The results suggest that multiple plant species coexistence could reduce lead accumulation in crop plants and alleviate the negative impacts on soil microbes in polluted land, thereby highlighting the significance of plant diversity in agroecosystems.

Genetic structure of the oriental white stork (Ciconia boyciana): implications for a breeding colony in a non-breeding area

The oriental white stork (Ciconia boyciana) is a threatened species, and their numbers are still in decline due tohabitat loss and poaching. China is a breeding and main wintering area for this animal and in recent years someindividuals have been found breeding in wintering areas and at some stopover sites. These new breeding coloniesare an exciting sign, however, little is understood of the genetic structure of this species. Based on the analysis ofa 463-bp mitochondrial DNA (mtDNA) control region, we investigated the genetic structure and genetic diversity of66 wild oriental white storks from a Chinese population. We analyzed the sequences of 66 storks obtained in thisstudy and the data of 17 storks from a Japanese population. Thirty-seven different haplotypes were detected amongthe 83 samples. An analysis of molecular variance showed a significant population subdivision between the twopopulations (FST = 0.316, P < 0.05). However, the phylogenetic analysis revealed that the samples from the differentpopulations did not form separate clusters and that there were genetic exchanges between the two populations.Compared with the Japanese population, the Chinese population had a relatively higher genetic diversity with ahaplotype diversity (h ± SD) of 0.953 ± 0.013 and a nucleotide diversity (π ± SD) of 0.013 ± 0.007. The high haplotypediversity and low nucleotide diversity indicate that this population might be in a rapidly increasing period from asmall effective population. A neighbor-joining tree analysis indicated that genetic exchange had occurred betweenthe newly arisen southern breeding colony and the northern breeding colony wintering in the middle and lowerYangtze River floodplain. These results have important implications for the conservation of the oriental white storkpopulation in China.

Effect of copper tolerant Elsholtzia splendens on bacterial community associated with Commelina communis on a copper mine spoil

Facilitation, or positive plant–plant interaction, has received increasing concern from ecologists over the last two decades. Facilitation may occur through direct mitigation of severe environments or indirect mediation by a third participant from the same or different trophic levels. The copper(Cu) tolerant species Elsholtzia splendens facilitates the establishment and growth of co-occurring Commelina communis through indirect enrichment of microbial activity. However, whether and how E. splendens impacts the microbial community that is associated with C. communis is less known. We characterized the soil bacterial community in the rhizosphere of C. communis in the absence and presence of E.splendens using PCR-DGGE(polymerase chain reaction-denaturing gradient gel electrophoresis) and sequencing. The result showed that the richness of the bacterial community increased, but diversity and evenness remained similar, in the presence of E. splendens.Chloroflexi, Acidobacteria and Proteobacteria were the most dominant bacteria. The relative abundance of dominant and minor bacterial groups showed distinctly different responses to E. splendens. Principal component analysis and redundancy analysis indicated that variation of the bacterial community was determined by multiple factors and might be driven by the tested soil parameters collectively, or alternatively changed through plant root exudates or other microorganisms. Our results enhance the understanding of how the bacterial community associated with a beneficiary plant responds to a benefactor plant and suggests that the changes of bacterial community composition may have far-reaching influence on plant–soil feedback and the aboveground plant community in the long run.