Influence of flanking genes on Gammaproteobacterial form I and II RubisCO functioning

Since the majority of all microorganisms are currently not culturable, we used a metagenomic approach to identify genes and enzymes associated with RubisCO expression. The investigated metagenomic DNA fragment originates from the deep-sea hydrothermal vent field Nibelungen at 8°18'S along the Mid-Atlantic Ridge. It is 13,023 bp and resembles genes from Thiomicrospira crunogena. The fragment encodes nine open reading frames (ORFs) which include two types of RubisCO, form I (CbbL/S) and form II (CbbM), two LysR transcriptional regulators (LysR1 and LysR2), two von Willebrand factor type A (CbbO-m and CbbO-1), and two AAA+ ATPases (CbbQ-m and CbbQ-1), expected to function as RubisCO activating enzymes. To date, only one study has ever investigated regulatory mechanisms in metagenome-derived RubisCO gene clusters (Böhnke and Perner 2015). Here, total RubisCO activity was significantly influenced when cbbL and cbbM neighboring genes were knocked out (Böhnke and Perner 2015), but it remained unclear which of the two RubisCOs was primarily affected by these mutations. Our study suggests that CbbQ-m and CbbO-m activate CbbL and that LysR1 and LysR2 proteins promote CbbQ-m/CbbO-m expression. CbbO-1 seems to activate CbbM and CbbM itself appears to contribute to intensifying LysR's binding ability and thus its own transcriptional regulation. CbbM furthermore appears to impair cbbL expression.