Enhanced PHB Accumulation in Photosystem- and Respiration-defective Mutants of a Cyanobacterium Synechocystis sp. PCC 6803

Synechocystis sp. PCC 6803의 에너지 대사 결함 돌연변이 균주에서의 Poly(3-hydroxybutyrate) 축적량 증진

  • Kim Soo-Youn (Department of Microbiology, Chungnam National University) ;
  • Choi Gang Guk (Department of Microbiology, Chungnam National University) ;
  • Park Youn Il (Department of Biology, Chungnam National University) ;
  • Park Young Mok (Biomolecular Research Team, Korea Basic Science Institute) ;
  • Yang Young Ki (Department of Genetic Engineering, Chosun University) ;
  • Rhee Young Ha (Department of Microbiology, Chungnam National University)
  • 김수연 (충북대학교 미생물학과) ;
  • 최강국 (충북대학교 미생물학과) ;
  • 박연일 (충남대학교 생물학과) ;
  • 박영목 (한국기초지원연구원 프로테옴분석팀) ;
  • 양영기 (조선대학교 유전공학과) ;
  • 이영하 (충북대학교 미생물학과)
  • Published : 2005.03.01

Abstract

Photoautotrophic bacteria are promising candidates for the production of poly(3-hydroxybutyrate) (PHB) since they can address the critical problem of substrate costs. In this study, we isolated 25 Tn5-inserted mutants of the Synechocystis sp. PCC 6803 which showed enhanced PHB accumulation compared to the wild-type strain. After 5-days cultivation under nitrogen-limited mixotrophic conditions, the intracellular levels of PHB content in these mutants reached up to $10-30\%$ of dry cell weight (DCW) comparable to $4\%$ of DCW in the wild-type strain. Using the method of inverse PCR, the affected genes of the mutants were mapped on the completely known genome sequence of Synechocystis sp. PCC 6803. As a result, the increased PHB accumulation in 5 mutants were found to be resulted from defects of genes coding for NADH-ubiquinone oxidoreductase, O-succinylbenzoic-CoA ligase, photosystem II PsbT protein or histidine kinase, which are involved in photosystem in thylakoid inner membrane of the cell. The values of $NAD(P)H/NAD(P)^+$ ratio in the cells of these mutants were much higher than that of the wild-type strain as measured by using pulse-amplitude modulated fluorometer, suggesting that PHB synthesis could be enhanced by increasing the level of cellular NAD(P)H which is a limiting substrate for NADPH-dependent acetoacetyl-CoA reductase. From these results, it is likely that NAD(P)H would be a limiting factor for PHB synthesis in Synechocystis sp. PCC 6803.

Keywords

NADPH/NADP+ ratio;poly(3-hydroxybutyrate);Synechocystis sp. PCC 6803;transposon mutagenesis

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