Ribulose bisphosphate carboxylase activity and a Calvin cycle gene cluster in Sulfobacillus species

Department of Biological Sciences, University of Warwick, Coventry CV4 7AL, UK Correspondence Paul R. Norris P.R.Norris{at}warwick.ac.uk The Calvin–Benson–Bassham (CBB) cycle has been extensively studied in proteobacteria, cyanobacteria, algae and plants, but hardly at all in Gram-positive bacteria. Some characteristics of ribulose bisphosphate carboxylase/oxygenase (RuBisCO) and a cluster of potential CBB cycle genes in a Gram-positive bacterium are described in this study with two species of Sulfobacillus (Gram-positive, facultatively autotrophic, mineral sulfide-oxidizing acidophiles). In contrast to the Gram-negative, iron-oxidizing acidophile Acidithiobacillus ferrooxidans , Sulfobacillus thermosulfidooxidans grew poorly autotrophically unless the CO 2 concentration was enhanced over that in air. However, the RuBisCO of each organism showed similar affinities for CO 2 and for ribulose 1,5-bisphosphate, and similar apparent derepression of activity under CO 2 limitation. The red-type, form I RuBisCO of Sulfobacillus acidophilus was confirmed as closely related to that of the anoxygenic phototroph Oscillochloris trichoides . Eight genes potentially involved in the CBB cycle in S. acidophilus were clustered in the order cbbA , cbbP , cbbE , cbbL , cbbS , cbbX , cbbG and cbbT . Abbreviations: CBB, Calvin–Benson–Bassham; CTAB, cetyl trimethylammonium bromide; FBP, fructose-1,6-bisphosphate; GAP, glyceraldehyde-3-phosphate dehydrogenase; PEP, phosphoenolpyruvate; PRK, phosphoribulokinase; RPE, ribulose-5-phosphate-3-epimerase; RuBisCO, ribulose bisphosphate carboxylase/oxygenase; RuBP, ribulose 1,5-bisphosphate; SD, Shine–Dalgarno Present address: Mathys and Squire, Patent Attorneys, 120, Holborn, London EC1N 2SQ, UK. The GenBank accession number of the S. acidophilus genomic DNA sequence containing putative cbb genes and flanking sequences is U75301.