IpdE1-IpdE2 Is a Heterotetrameric Acyl Coenzyme A Dehydrogenase That Is Widely Distributed in Steroid-Degrading Bacteria.

Steroid-degrading bacteria, including Mycobacterium tuberculosis (Mtb), utilize an architecturally distinct subfamily of acyl coenzyme A dehydrogenases (ACADs) for steroid catabolism. These ACADs are α2ß2 heterotetramers that are usually encoded by adjacent fadE-like genes. In mycobacteria, ipdE1 and ipdE2 (formerly fadE30 and fadE33) occur in divergently transcribed operons associated with the catabolism of 3aα-H-4α(3'-propanoate)-7aß-methylhexahydro-1,5-indanedione (HIP), a steroid metabolite. In Mycobacterium smegmatis, ΔipdE1 and ΔipdE2 mutants had similar phenotypes, showing impaired growth on cholesterol and accumulating 5-OH HIP in the culture supernatant. Bioinformatic analyses revealed that IpdE1 and IpdE2 share many of the features of the α- and ß-subunits, respectively, of heterotetrameric ACADs that are encoded by adjacent genes in many steroid-degrading proteobacteria. When coproduced in a rhodococcal strain, IpdE1 and IpdE2 of Mtb formed a complex that catalyzed the dehydrogenation of 5OH-HIP coenzyme A (5OH-HIP-CoA) to 5OH-3aα-H-4α(3'-prop-1-enoate)-7aß-methylhexa-hydro-1,5-indanedione coenzyme A ((E)-5OH-HIPE-CoA). This corresponds to the initial step in the pathway that leads to degradation of steroid C and D rings via ß-oxidation. Small-angle X-ray scattering revealed that the IpdE1-IpdE2 complex was an α2ß2 heterotetramer typical of other ACADs involved in steroid catabolism. These results provide insight into an important class of steroid catabolic enzymes and a potential virulence determinant in Mtb.

Core sediments and oil chemistry from contaminated mangroves in eastern Niger Delta, Ogoniland, Nigeria.

Thirty cores to maximum depth of 3.7 m were taken in 2018 to investigate sedimentary characteristics and hydrocarbon penetration within mangrove sediments in Bodo (southeastern Niger Delta), an area contaminated by numerous ongoing oil spills but most significantly in 2008. Sediments were dominated by organically rich (Chikoko) mud underlain by clay with sandier sediments at deeper core depths and adjacent to shorelines. Analysis of 202 samples showed high median hydrocarbon concentrations at the surface (39,000 mg/kg) and shallow subsurface (10-25 cm, 25,000 mg/kg), decreasing with depth: 430 mg/kg at 40-70 cm; 157 mg/kg at 75-120 cm, and <30 mg/kg at depths ≥150 cm. Most (85%) EPA-16 priority polycyclic aromatic hydrocarbons and all monoaromatics were below detection limit. Shallow subsurface oil penetration was aided by crab burrows and presence of mangrove remnants and was inhibited from deeper depths by groundwater at ~25 cm and increased sediment compaction.