(R)-Cysteate-nitrogen assimilation by Cupriavidus necator H16 with excretion of 3-sulfolactate: a patchwork pathway

Arch Microbiol. 2012 Nov;194(11):949-57. doi: 10.1007/s00203-012-0825-y. Epub 2012 Jul 15.

Abstract

Cupriavidus necator H16 grew exponentially with (R)-cysteate, a structural analogue of aspartate, as sole source of nitrogen in succinate-salts medium. Utilization of cysteate was quantitative and concomitant with growth and with the excretion of the deaminated product (R)-sulfolactate, which was identified thoroughly. The deaminative pathway started with transport of (R)-cysteate into the cell, which we attributed to an aspartate transporter. Transamination to sulfopyruvate involved an aspartate/(R)-cysteate:2-oxoglutarate aminotransferase (Aoa/Coa) and regeneration of the amino group acceptor by NADP⁺-coupled glutamate dehydrogenase. Reduction of sulfopyruvate to (R)-sulfolactate was catalyzed by a (S)-malate/(R)-sulfolactate dehydrogenase (Mdh/Sdh). Excretion of the sulfolactate could be attributed to the sulfite/organosulfonate exporter TauE, which was co-encoded and co-expressed, with sulfoacetaldehyde acetyltransferase (Xsc), though Xsc was irrelevant to the current pathway. The metabolic enzymes could be assayed biochemically. Aoa/Coa and Mdh/Sdh were highly enriched by protein separation, partly characterized, and the relevant locus-tags identified by peptide-mass fingerprinting. Finally, RT-PCR was used to confirm the transcription of all appropriate genes. We thus demonstrated that Cupriavidus necator H16 uses a patchwork pathway by recruitment of 'housekeeping' genes and sulfoacetaldehyde-degradative genes to scavenge for (R)-cysteate-nitrogen.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Bacterial Proteins / genetics
  • Bacterial Proteins / metabolism*
  • Cupriavidus necator / enzymology
  • Cupriavidus necator / genetics*
  • Cupriavidus necator / growth & development
  • Cupriavidus necator / metabolism*
  • Cysteic Acid / metabolism*
  • Gene Expression Regulation, Bacterial
  • Lactates / metabolism*
  • Nitrogen / metabolism*

Substances

  • Bacterial Proteins
  • Lactates
  • Cysteic Acid
  • Nitrogen