ABSTRACT
Arsenic is known as a toxic metalloid, which mainly exists in inorganic forms such as arsenite and arsenate in the natural environment. A number of microorganisms have evolved different resistant mechanisms for arsenic detoxification to cope with the widespread distribution of the poisonous arsenic. Four distinct microbial arsenic-resistant mechanisms have been described including As(III) oxidation, cytoplasmic As(V) reduction, respiratory As(V) reduction, and As(III) methylation. These mechanisms confer arsenic resistance in microorganisms that play important roles in the transformation and geological cycle of arsenic. This review mainly focuses on the researches on these molecular mechanisms and potential application for environmental arsenic bioremediation using microorganisms.
ABSTRACT
Manganese-oxidizing microorganisms are able to oxidize soluble Mn(II) into insoluble Mn oxides. Such microorganisms are very useful in treatment of Mn-contaminated water. In this research, a Mn(II)- oxidizing bacterium Bacillus sp. MK3-1 was isolated from Mn-contaminated soil. This bacterium has high MnCl2 resistance with a MIC of 20 mmol/L. The results showed that it is able to oxidize and remove more than 96% of Mn(II) in the culture medium. The immobilized solid-embedding Bacillus sp. MK3-1can re- moved 87.12% of manganese contaminated water. The final concentration of MnCl2 after the treatment reached the national discharge standard level. Scan electron microscope observation showed that the pro- duced Mn oxides located on the cell surfaces of Bacillus sp. MK3-1. Energy dispersive spectrdmeter analy- sis indicated that the content of manganese of cell surfaces of Bacillus sp. MK3-1 was 19.60% (W/W). At last we amplified a 903 bp multicopper oxidase gene mnxG encoding the putative Mn(II)-oxidizing protein.The product of mnxG showed 86% identity to the reported multicopper oxidase.
ABSTRACT
Halophilic microorganisms play important rules in salt field ecosystem and salt production. In this study, halophilic bacteria and haloarchaea from soils of Lianyungang Taibei and Yancheng Sanwei salt fields were analyzed. The halophilic bacterial and haloarchaeal types from both the soils were similar, but each soil had its distinctive species. A total of 17 halophilic bacteria were identified, among them, Halomonas was found from both the soils, while Pontibacillus and Halobacillus were isolated from Sanwei salt field only. Using uncultured 16S rRNA gene library technology, 13 haloarchaeal soil 16S rRNA genes were identified from both the saline soils. Halobacterium and Haloplanus were found from Taibei salt field, while Halobac- terium, Natronobacterium, Halogeometricum and Haloarcula were identified from Sanwei salt field. Ten haloarchaeal 16S rRNA gene sequences showed 92%~97% identities with the GenBank sequences that ap- pear to represent novel soil haloarchaeal species. This study provides important information that is useful for further investigation and application of halophiles of saline soil fields.