Xueling Wu

Complete degradation of di-n-octyl phthalate by biochemical cooperation between Gordonia sp. strain JDC-2 and Arthrobacter sp. strain JDC-32 isolated from activated sludge

Two bacterial strains were isolated from activated sludge using mixtures of phthalic acid esters (PAEs) as the sole source of carbon and energy. One of the isolates was identified as Gordonia sp. strain JDC-2 and the other as Arthrobacter sp. strain JDC-32, mainly through 16S rRNA gene sequence analysis. Gordonia sp. strain JDC-2 rapidly degraded di-n-octyl phthalate (DOP) into phthalic acid (PA), which accumulated in the culture medium. Arthrobacter sp. strain JDC-32 degraded PA but not DOP. The co-culture of Gordonia sp. strain JDC-2 and Arthrobacter sp. strain JDC-32 degraded DOP completely by overcoming the degradative limitations of each species alone. The biochemical pathway of DOP degradation by Gordonia sp. strain JDC-2 was proposed based on the identified degradation intermediates. The results suggest that DOP is completely degraded by the biochemical cooperation of different microorganisms isolated from activated sludge.

Isolation and identification of a strain ofLeptospirillum ferriphilum from an extreme acid mine drainage site

Based on a new selective isolation strategy that mimicked physiological characteristics of leptospirilla, such as pH, temperature and its less sensitivity to the high ferric-ferrous iron ratio, a bacterial strain, called strain YSK, was isolated from an extreme acid mine drainage (AMD) site. Cells were Gram-negative, small curved rods measuring 0.27–0.52 by 0.81–3.17 μm. The cell shape suggested that strain YSK was likely a strain ofLeptospirillum ferrooxidans. However, based on the 16S rDNA sequence analysis, strain YSK possessed 100% sequence similarity with that of the typicalLeptospirillum ferriphilum strain Fairview; furthermore, the G+C content, the size of the 16S–23S rRNA gene spacer regions and the ability to grow at 45°C further indicated that strain YSK belonged to the speciesLeptospirillum ferriphilum.

Genetic diversity of phthalic acid esters-degrading bacteria isolated from different geographical regions of China

Thirty-two strains of phthalic acid ester (PAEs)-degrading bacteria were isolated from thirteen geographically diverse sites by enrichment using mixtures of PAEs as the sole source of carbon and energy. Sequence analyses of the 16S rRNA gene indicated that these isolates were from six genera (Arthrobacter, Gordonia, Rhodococcus, Acinetobacter, Pseudomonas, and Delftia). To evaluate the genetic diversity among them, the molecular typing method rep-PCR with primers based on enterobacterial repetitive intergenic consensus, repetitive extragenic palindromes, and BOXAIR sequences was performed. Strain-specific and unique genotypic fingerprints were distinguished for most of these isolates. In addition, utilization of various PAEs and the central intermediate phthalic acid by representative isolates suggested inter-isolate differences in the substrate utilization and degradation pathways. Furthermore, HPLC analysis showed that the rate of dimethyl phthalate degradation varied from 48.32 to 100% between strains. These results suggest a high level of genetic diversity among PAEs-degrading bacteria in the natural environment and their great potential to clean up phthalates-contaminated environments.

Phylogenetic and genetic characterization of Acidithiobacillus strains isolated from different environments

AbstractTo study the phylogenetic relationships and genetic heterogeneity of 21 Acidithiobacillus strains isolated from different environments, we amplified and sequenced the 16S–23S rRNA gene intergenic spacers (ITS) of all these strains. These sequence data, combined with related sequences available from GenBank, were divided into six phylogenetic groups by 16S rRNA gene and by 16S–23S rRNA gene sequence analysis. The results of phylogenetic analysis were consistent with those obtained by repetitive element PCR and arbitrarily primed PCR. In this research, the Acidithiobacillus ferrooxidans (A.ferrooxidans) strains were always separated into two groups in phylogenetic and cluster analyses. Genotypic analyses of the genes rusA, rusB, hip and iro suggest that these two groups may have different biochemical mechanisms for oxidizing ferrous iron. Strains in one A. ferrooxidans group were detected with rusA gene that encodes rusticyanin A which plays a very important role in the iron respiratory chain. The second A. ferrooxidans group was found to contain rusB gene which encode a homologous protein (RusB). The data suggested that ITS-based phylogeny is an effective tool to elucidate the relationships of Acidithiobacillus and that a different iron oxidation pathway may exist in different A. ferrooxidans groups.