Abstract
Rhodococcus erythropolis MI2 has the extraordinary ability to utilize the xenobiotic 4,4´-dithiodibutyric acid (DTDB). Cleavage of DTDB by the disulfide-reductase Nox, which is the only verified enzyme involved in DTDB-degradation, raised 4-mercaptobutyric acid (4MB). 4MB could act as building block of a novel polythioester with unknown properties. To completely unravel the catabolism of DTDB, the genome of R. erythropolis MI2 was sequenced, and subsequently the proteome was analyzed. The draft genome sequence consists of approximately 7.2 Mbp with an overall G+C content of 62.25% and 6,859 predicted protein-encoding genes. The genome of strain MI2 is composed of three replicons: one chromosome and two megaplasmids with sizes of 6.45, 0.4 and 0.35 Mbp, respectively. When cells of strain MI2 were cultivated with DTDB as sole carbon source and compared to cells grown with succinate, several interesting proteins with significantly higher expression levels were identified using 2D-PAGE and MALDI-TOF mass spectrometry. A putative luciferase-like monooxygenase-class F420-dependent oxidoreductase (RERY_05640), which is encoded by one of the 126 monooxygenase-encoding genes of the MI2-genome, showed a 3-fold increased expression level. This monooxygenase could oxidize the intermediate 4MB into 4-oxo-4-sulfanylbutyric acid. Next, a desulfurization step, which forms succinic acid and volatile hydrogen sulfide, is proposed. One gene coding for a putative desulfhydrase (RERY_06500) was identified in the genome of strain MI2. However, the gene product was not recognized in the proteome analyses. But, a significant expression level with a ratio of up to 7.3 was determined for a putative sulfide:quinone oxidoreductase (RERY_02710), which could also be involved in the abstraction of the sulfur group. As response to the toxicity of the intermediates, several stress response proteins were strongly expressed, including a superoxide dismutase (RERY_05600) and an osmotically induced protein (RERY_02670). Accordingly, novel insights in the catabolic pathway of DTDB were gained.
Highlights
Rhodococcus erythropolis strain MI2 is a Gram-positive, aerobic and non-motile bacterium belonging to the family Nocardiaceae, which contains highly diverse genera and species [1, 2]
Clusters marked at the position “I” and “II” represent genes that could play a vital role in the degradation pathway of dithiodibutyric acid (DTDB) and will be discussed later
The transport system is still uncertain, but DTDB is initially cleaved by the action of Nox (RERY_03780) giving 4-mercaptobutyric acid (4MB), which is oxidized forming 4-oxo-4-sulfanylbutyric acid via the LLMMI2 F420-dependent enzyme (RERY_05640)
Summary
Rhodococcus erythropolis strain MI2 is a Gram-positive, aerobic and non-motile bacterium belonging to the family Nocardiaceae, which contains highly diverse genera and species [1, 2]. R. erythropolis strain MI2 was isolated, and later applied in polythioester (PTE) research, because this strain exhibits the rare ability to use the synthetic disulfide 4,4 ́-dithiodibutyric acid (DTDB) as sole carbon source and electron donor for aerobic growth [9, 10]. For the generation of metabolically engineered PTE-production strains, it is necessary to investigate the microbial catabolism of DTDB. This nontoxic PTE-precursor substrate could result in the formation of the hitherto unknown poly(4-mercaptobutyric acid) (poly[4MB]), which would be the first PTE consisting of 4-mercaptoalkanoate building blocks and is expected to exhibit interesting new features
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
