1887

Abstract

sp. ATCC 51142 is an aerobic N-fixing and hydrogen-producing cyanobacterium. Isotopomer analysis of its amino acids revealed an identical labelling profile for leucine and isoleucine when 51142 was grown mixotrophically using 2-C-labelled glycerol as the main carbon source. This indicated that 51142 employs the atypical alternative citramalate pathway for isoleucine synthesis, with pyruvate and acetyl-CoA as precursors. Utilization of the citramalate pathway was confirmed by an enzyme assay and LC-MS/MS analysis. Furthermore, the genome sequence of 51142 shows that the gene encoding the key enzyme (threonine ammonia-lyase) in the normal isoleucine pathway is missing. Instead, the cce_0248 gene in 51142 exhibits 53 % identity to the gene encoding citramalate synthase (CimA, GSU1798) from . Reverse-transcription PCR indicated that the cce_0248 gene is expressed and its transcriptional level is lower in medium with isoleucine than in isoleucine-free medium. Additionally, a search for citramalate synthase and threonine ammonia-lyase implies that this alternative isoleucine synthesis pathway may be present in other cyanobacteria, such as and . This suggests that the pathway is more widespread than originally thought, as previous identifications of the citramalate pathway are limited to mostly anaerobic bacteria or archaea. Furthermore, this discovery opens the possibility that such autrotrophic micro-organisms may be engineered for robust butanol and propanol production from 2-ketobutyrate, which is an intermediate in the isoleucine biosynthesis pathway.

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2010-02-01
2019-10-14
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vol. , part 2, pp. 596 - 602

[ PDF, 71 kb], including: Determination of citramalate labelling pattern Gel profiles of RT-PCR products



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