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Articles by Xiuzhu Dong
Total Records ( 2 ) for Xiuzhu Dong
  Guishan Zhang , Na Jiang , Xiaoli Liu and Xiuzhu Dong
  The Zoige wetland of the Tibetan plateau is at permanent low temperatures and is a methane emission heartland of the plateau; however, cold-adaptive methanogens in the soil are poorly understood. In this study, a variety of methanogenic enrichments at 15°C and 30°C were obtained from the wetland soil. It was demonstrated that hydrogenotrophic methanogenesis was the most efficient type at 30°C, while methanol supported the highest methanogenesis rate at 15°C. Moreover, methanol was the only substrate to produce methane more efficiently at 15°C than at 30°C. A novel psychrophilic methanogen, strain R15, was isolated from the methanol enrichment at 15°C. Phylogenetic analysis placed strain R15 within the genus Methanolobus, loosely clustered with Methanolobus taylorii (96.7% 16S rRNA similarity). R15 produced methane from methanol, trimethylamine, and methyl sulfide and differed from other Methanolobus species by growing and producing methane optimally at 18°C (specific growth rate of 0.063 ± 0.001 h–1) and even at 0°C. Based on these characteristics, R15 was proposed to be a new species and named "Methanolobus psychrophilus" sp. nov. The Km and Vmax of R15 for methanol conversion were determined to be 87.5 ± 0.4 µM and 0.39 ± 0.04 mM h–1 at 18°C, respectively, indicating a high affinity and conversion efficiency for methanol. The proportion of R15 in the soil was determined by quantitative PCR, and it accounted for 17.2% ± 2.1% of the total archaea, enumerated as 107 per gram of soil; the proportion was increased to 42.4% ± 2.3% in the methanol enrichment at 15°C. This study suggests that the psychrophilic methanogens in the Zoige wetland are likely to be methylotrophic and to play a role in methane emission of the wetland.
  Huichun Tong , Wei Chen , Wenyuan Shi , Fengxia Qi and Xiuzhu Dong
  We previously demonstrated that Streptococcus oligofermentans suppressed the growth of Streptococcus mutans, the primary cariogenic pathogen, by producing hydrogen peroxide (H2O2) through lactate oxidase activity. In this study, we found that the lox mutant of S. oligofermentans regained the inhibition while growing on peptone-rich plates. Further studies demonstrated that the H2O2 produced on peptone by S. oligofermentans was mainly derived from seven L-amino acids, i.e., L-aspartic acid, L-tryptophan, L-lysine, L-isoleucine, L-arginine, L-asparagine, and L-glutamine, indicating the possible existence of L-amino acid oxidase (LAAO) that can produce H2O2 from L-amino acids. Through searching the S. oligofermentans genome for open reading frames with a conserved flavin adenine dinucleotide binding motif that exists in the known LAAOs, including those of snake venom, fungi, and bacteria, a putative LAAO gene, assigned as aaoSo, was cloned and overexpressed in Escherichia coli. The purified protein, SO-LAAO, showed a molecular mass of 43 kDa in sodium dodecyl sulfate-polyacrylamide gel electrophoresis and catalyzed H2O2 formation from the seven L-amino acids determined above, thus confirming its LAAO activity. The SO-LAAO identified in S. oligofermentans differed evidently from the known LAAOs in both substrate profile and sequence, suggesting that it could represent a novel LAAO. An aaoSo mutant of S. oligofermentans did lose H2O2 formation from the seven L-amino acids, further verifying its function as an LAAO. Furthermore, the inhibition by S. oligofermentans of S. mutans in a peptone-rich mixed-species biofilm was greatly reduced for the aaoSo mutant, indicating the gene`s importance in interspecies competition.
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