Abstract
A bacterial homolog of the mammalian mitochondrial benzodiazepine receptor, the tryptophan-rich sensory protein (TspO) has been previously demonstrated to negatively affect the transcriptional expression of several photosynthesis genes of Rhodobacter sphaeroides. To identify components of the signal transduction pathway from the outer membrane-localized TspO to the DNA-active transcription factor(s), we examined the involvement of TspO in the regulation of tetrapyrrole metabolism in R. sphaeroides. By analyzing the tetrapyrrole pigments accumulated by resting cell suspensions of R. sphaeroides, we demonstrated that TspO negatively regulates the activity of coproporphyrinogen III oxidase in this bacterium. hemN, encoding one of the isoenzymes of coproporphyrinogen III oxidase of R. sphaeroides, provided in trans to the wild type strain, produced a TSPO1 mutant phenotype by abolishing the negative effect of TspO on the transcription of the photosynthesis genes, crtI and puc. It is proposed that TspO, by regulating the exit of certain tetrapyrrole intermediates of the heme/bacteriochlorophyll biosynthetic pathways in R. sphaeroides in response to the availability of molecular oxygen, causes the accumulation of a biosynthetic intermediate that serves as a corepressor for both specific pigment gene transcription and the puc operon. The relationship between the bacterial TspO and the mitochondrial peripheral benzodiazepine receptor is discussed.
Highlights
Rhodobacter sphaeroides is a facultative phototrophic bacterium capable of growth both aerobically and anaerobically
Our preliminary studies revealed no significant differences in the accumulation of heme pigments by either the wild type or TSPO1 cells grown under these conditions
Because wild type cells of R. sphaeroides accumulate predominantly uroporphyrin and its decarboxylation products but only small amounts of protoporphyrin when incubated in the presence of aminolevulinic acid (ALA) aerobically, it seemed likely that the activity of coproporphyrinogen III oxidase and not protoporphyrinogen oxidase was affected in the TSPO1 mutant strain
Summary
Cultures of R. sphaeroides 2.4.1 and its derivatives were grown in Sistrom’s minimal medium A containing 0.4% succinate as a carbon source [11] as described previously [12]. -Galactosidase Activity in Cell Extracts—R. sphaeroides cultures were grown to a cell density of approximately 1.8 ϫ 108 cells/ml, and chloramphenicol was added to a final concentration of 80 g/ml to terminate protein synthesis. Assay of -galactosidase activity in cell extracts was performed as described previously [15]. Preparation of Resting Cell Suspensions—R. sphaeroides cells were grown either aerobically or photosynthetically to a cell density of approximately 1.8 ϫ 108 cells/ml, harvested by centrifugation (15 min, 10,000 ϫ g, 10 °C), washed with 0.1 M potassium phosphate buffer, pH 7.4, and resuspended in the same buffer containing 80 g/ml chloramphenicol to terminate protein synthesis.
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
