Original Paper

Archives of Microbiology

, Volume 182, Issue 1, pp 18-29

First online:

Characterization and expression of genes from the RubisCO gene cluster of the chemoautotrophic symbiont of Solemya velum: cbbLSQO

  • Julie SchwedockAffiliated withDepartment of Organismic and Evolutionary Biology, Harvard UniversityGenomic Profiling Systems
  • , Tara L. HarmerAffiliated withDepartment of Organismic and Evolutionary Biology, Harvard University
  • , Kathleen M. ScottAffiliated withDepartment of Organismic and Evolutionary Biology, Harvard UniversityDepartment of Biology, University of South Florida
  • , Harm J. HektorAffiliated withDepartment of Organismic and Evolutionary Biology, Harvard University
  • , Angelica P. SeitzAffiliated withDepartment of Organismic and Evolutionary Biology, Harvard University
  • , Matthew C. FontanaAffiliated withDepartment of Organismic and Evolutionary Biology, Harvard University
  • , Daniel L. DistelAffiliated withDepartment of Organismic and Evolutionary Biology, Harvard UniversityDepartment of Biochemistry, Microbiology, and Molecular Biology, University of Maine
  • , Colleen M. CavanaughAffiliated withDepartment of Organismic and Evolutionary Biology, Harvard University Email author 

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Abstract

Chemoautotrophic endosymbionts residing in Solemya velum gills provide this shallow water clam with most of its nutritional requirements. The cbb gene cluster of the S. velum symbiont, including cbbL and cbbS, which encode the large and small subunits of the carbon-fixing enzyme ribulose 1,5-bisphosphate carboxylase/oxygenase (RubisCO), was cloned and expressed in Escherichia coli. The recombinant RubisCO had a high specific activity, ∼3 μmol min−1 mg protein −1, and a K CO2 of 40.3 μM. Based on sequence identity and phylogenetic analyses, these genes encode a form IA RubisCO, both subunits of which are closely related to those of the symbiont of the deep-sea hydrothermal vent gastropod Alviniconcha hessleri and the photosynthetic bacterium Allochromatium vinosum. In the cbb gene cluster of the S. velum symbiont, the cbbLS genes were followed by cbbQ and cbbO, which are found in some but not all cbb gene clusters and whose products are implicated in enhancing RubisCO activity post-translationally. cbbQ shares sequence similarity with nirQ and norQ, found in denitrification clusters of Pseudomonas stutzeri and Paracoccus denitrificans. The 3′ region of cbbO from the S. velum symbiont, like that of the three other known cbbO genes, shares similarity to the 3′ region of norD in the denitrification cluster. This is the first study to explore the cbb gene structure for a chemoautotrophic endosymbiont, which is critical both as an initial step in evaluating cbb operon structure in chemoautotrophic endosymbionts and in understanding the patterns and forces governing RubisCO evolution and physiology.

Keywords

RubisCO Symbiosis Chemosynthesis Solemya velum Ribulose 1,5-bisphosphate carboxylase/oxygenase K CO2