A redundant isoprenoid biosynthetic pathway supports metabolic versatility.

UNLABELLED

Isoprenoids are ubiquitous molecules that serve as fundamental building blocks for life. In bacteria, isoprenoids are precursors for carotenoid pigments, respiratory cofactors, and essential sugar carrier lipids, such as lipid II. Isoprenoid synthesis initiates via condensation of the five-carbon (C) precursors, isopentenyl diphosphate (IPP) and dimethylallyl diphosphate (DMAPP). This initial reaction condenses one DMAPP and two IPPs, resulting in C farnesyl diphosphate (FPP), an intermediate that is sequentially elongated with IPP. FPP is thought to be synthesized exclusively by the prenyl diphosphate synthase (PDS), IspA. In , mutants lack the golden carotenoid pigment, staphyloxanthin. The fact that can be inactivated in and other bacteria is surprising given the reliance of lipid II on FPP and supports the hypothesis that an additional enzyme produces the critical isoprenoid precursor. We isolated pigmented suppressor mutants harboring single-nucleotide polymorphisms within a second PDS-encoding gene, , suggesting that HepT and IspA have overlapping roles in isoprenoid synthesis. Subsequent work determined that IspA and HepT support metabolic versatility, as a double mutant fails to aerobically respire partially due to a lack of prenylated heme cofactors. The finding that a double mutant is viable supports a model whereby a third PDS compensates in the absence of and to produce lipid II precursors. Lastly, we show that and mutants exhibit colonization defects in a murine model of systemic infection, demonstrating that isoprenoid biosynthesis is a potential drug target for combating .

IMPORTANCE

Isoprenoid synthesis is an essential process that is presumed to be initiated by the prenyl diphosphate synthase (PDS), IspA. However, our understanding of this pathway is incomplete considering that mutants have been described in several bacterial species, leaving the mechanism for isoprenoid synthesis initiation uncertain in these genetic backgrounds. Using the opportunistic pathogen , we demonstrate that a second PDS, HepT, supports the production of isoprenoid-dependent molecules in the absence of IspA. Importantly, we show that mutants deficient for either IspA or HepT display colonization defects in a murine model of systemic infection. Furthermore, the simultaneous mutation of and is tolerated in and suggests the presence of a third PDS capable of initiating isoprenoid synthesis. This study establishes PDSs as viable targets for the treatment of infections and provides novel insights into the redundant nature of isoprenoid synthesis in this pathogen.