Wenliang Xiang

Screening a novel Na+/H+ antiporter gene from a metagenomic library of halophiles colonizing in the Dagong Ancient Brine Well in China.

Metagenomic DNA libraries constructed from the Dagong Ancient Brine Well were screened for genes with Na(+)/H(+) antiporter activity on the antiporter-deficient Escherichia coli KNabc strain. One clone with a stable Na(+)-resistant phenotype was obtained and its Na(+)/H(+) antiporter gene was sequenced and designated as m-nha. The deduced amino acid sequence of M-Nha protein consists of 523 residues with a calculated molecular weight of 58 147 Da and a pI of 5.50, which is homologous with NhaH from Halobacillus dabanensis D-8(T) (92%) and Halobacillus aidingensis AD-6(T) (86%), and with Nhe2 from Bacillus sp. NRRL B-14911 (64%). It had a hydropathy profile with 10 putative transmembrane domains and a long carboxyl terminal hydrophilic tail of 140 amino acid residues, similar to Nhap from Synechocystis sp. and Aphanothece halophytica, as well as NhaG from Bacillus subtilis. The m-nha gene in the antiporter-negative mutant E. coli KNabc conferred resistance to Na(+) and the ability to grow under alkaline conditions. The difference in amino acid sequence and the putative secondary structure suggested that the m-nha isolated from the Dagong Ancient Brine Well in this study was a novel Na(+)/H(+) antiporter gene.

Temporal heterogeneity of prokaryotic micro-organism communities in sediment of traditional freshwater cultured fish ponds in Southwest China

ABSTRACT The temporal heterogeneity of prokaryotic microorganism communities in sediment of traditional freshwater cultured fish ponds in Southwest China were investigated by 16S rRNA clone libraries. The result indicated that a total of 47 archaea clones and 392 bacterial clones were recovered from three samples, among them, the bacteria Mitsuaria chitosanitabida, Prolixibacter bellariivorans and Flavihumibacter petaseus and archaea Methanoregula formicica were dominant in the cultivation 1 year (Y1) sample, the bacteria Cetobacterium somerae, Allochromatium vinosum and Rhabdochromatium marinum and archaea Methanolinea tarda were dominant in the cultivation 2 years (Y2) sample, the bacteria Cetobacterium somerae and Bacteroides fragilis and archaea Methanolinea tarda were dominant in the cultivation 4 years (Y4) sample. The Shannon–Wiener (H) diversity index and the Simpson dominancy index respectively varied from 2.23 to 2.37 and from 7.30 to 9.04 for three gene libraries. Maximum operational taxonomic unit (OTU) richness was respectively estimated with two different models SChao1 and SACE, and it revealed SChao1 15 and SACE 15 for Y1, SChao1 15.25 and SACE 15 for Y2, SChao1 12 and SACE 12 for Y4. However, the B. fragilis which was found in the Y4 sample was 99% similar to the human and animal pathogen B. fragilis. No pathogenic organisms related to humans or animals were found at any other sample. Mentionable, the more detailed information about the safety of fish pond cultivation environment should receive more attention and further studies.