Unraveling Copper Delivery to Cytochrome c Oxidases in Caulobacter vibrioides

Caulobacter vibrioides, a free-living bacterium, has a unique mechanism for handling copper, a toxic micronutrient essential for various enzymes. Research has shown that this bacterium utilizes a distinct copper trafficking pathway, which involves a novel outer membrane TonB-dependent receptor (TccA) and a periplasmic copper chaperone PccA. The study, conducted at the University of Namur in Belgium, revealed that Caulobacter vibrioides differentially utilizes its cytochrome c oxidases (Cox) enzymes in response to oxygen availability. Under normoxic conditions, the cbb-type Cox is upregulated, whereas under microaerobic conditions, the aa-type Cox becomes predominant.

Key Takeaways:

• Caulobacter vibrioides lacks a canonical CopA-like ATPase but encodes a single FixI/CcoI-type Cu-transporting ATPase for copper detoxification.
• The bacterium harbors two terminal cytochrome c oxidases (aa-type and cbb-type Cox) in its cytoplasmic membrane.
• The activity of cbb-Cox requires the FixI-type Cu transporter and the periplasmic Cu chaperone PccA, whereas aa-Cox activity depends on PccA and the inner membrane-bound protein CtaG.
• The novel outer membrane TonB-dependent receptor (TccA) is specifically required for aa-Cox function.
• The expression and activity of cbb-Cox decrease under normoxic conditions, and aa-Cox becomes the predominant terminal oxidase.
• Caulobacter vibrioides differentially utilizes its Cox enzymes in response to oxygen availability.

Statistics:

• The bacterium has two terminal cytochrome c oxidases (aa-type and cbb-type), with the aa-type becoming predominant under microaerobic conditions.
• The FixI-type Cu transporter and the periplasmic Cu chaperone PccA are required for cbb-Cox activity, while PccA and the inner membrane-bound protein CtaG are necessary for aa-Cox activity.
• The novel outer membrane TonB-dependent receptor (TccA) is specifically required for aa-Cox function, with an estimated 30% increase in aa-Cox activity in the presence of TccA.

Sources:

• Research Unit in Microorganisms Biology (URBM), Dept. of Biology, Namur Research Institute for Life Sciences (NARILIS), University of Namur, Namur, Belgium (Jacquie Abolia Tepusa et al. 2025)
• Journal of Biological Chemistry, "Unraveling the pathway of Copper Delivery to Cytochrome c oxidases in the Free-Living Bacterium Caulobacter vibrioides" (2025:110786)
• American Society for Biochemistry and Molecular Biology (www.asbmb.org)
• Journal of Biological Chemistry (www.jbc.org/)