Photosynthetic genes in Rhodobacter capsulatus can be regulated by oxygen during dark respiratory growth with dimethylsulphoxide

Abstract

In the purple non-sulphur bacterium Rhodobacter capsulatus, genes encoding structural polypeptides of the lightharvesting (LH) and reaction center (RC) complexes incorporated into an intracytoplasmic photosynthetic membrane are induced upon lowering the oxygen tension in the media of aerobically growing cultures. When cultures are grown microaerophilically in the dark, an intracytoplasmic photosynthetic membrane develops gratuitously if a terminal oxidant, such as dimethylsulphoxide (DMSO) is present in the medium. The purpose of the present study was to determine whether in these conditions, photosynthetic genes are completely derepressed or whether they are still inducible in response to a lowering of oxygen tension. Oxygen induction of mRNA for thepuf and puc operons was compared in dark aerobic cultures (20% 0,) shifted to low oxygen conditions (3% 0,) allowing growth microaerophilically with or without DMSO as an accessory terminal oxidant. The extent of the induction was similar in both growth conditions, 6 to 12-fold forpufA mRNA and at least 400-fold forpucBmRNA which encode the light-harvesting I (LHIa) and light-harvesting I1 (LHIIP) polypeptides, respectively. The puf and puc operons were also induced by low oxygen tension in a mutant strain blocked in an early step of bacteriochlorophyll (BChl) synthesis, suggesting that the presence of BChl may not be a prerequisite for the normal oxygen regulation of the genes encoding the structural polypeptides of the photosynthetic apparatus.

appA, a novel gene encoding a trans-acting factor involved in the regulation of photosynthesis gene expression in Rhodobacter sphaeroides 2.4.1

“…Role of AppA in Bchl biosynthesis. It has been observed for both R. sphaeroides and R. capsulatus that interference with the biosynthesis of Bchl results in a decline in Crt accumulation and puc operon expression (2,20,21,28). These observations point to a link between the accumulation of Bchl, or an intermediate in the Bchl biosynthetic pathway, and expression of other PS genes, including puc and crt.…”

“…This assumption seemed plausible because, similar to Bchl biosynthetic mutants, mutant APP11 was impaired in Bchl production and accumulated an intermediate(s) in Bchl biosynthesis. Such an involvement could have a secondary effect on expression of the PS genes, as has been previously documented (2,20,21,28), although the precise mechanism is unknown.…”

Putative Hydrogen Bond to Tyrosine M208 in Photosynthetic Reaction Centers from Rhodobacter capsulatus Significantly Slows Primary Charge Separation

“…Previous studies on Rp. viridis have shown that RC gene expression can be enhanced by growing cells under microaerophilic conditions in the dark. , A series of experiments determined the optimum dissolved oxygen level for maximum protein expression. Holding the dissolved oxygen level constant around 2% for the last few hours before harvesting cells around OD 660 ≈ 5 gave good protein expression (Figure S1 of the Supporting Information), about a 3-fold increase in protein yield (>60 mg purified protein per 4 L growth medium).…”

Genetic evidence that PpsR from Rhodobacter sphaeroides 2.4.1 functions as a repressor of puc and bchF expression

“…Because transcription of the puc operon is known to be influenced by alterations in photopigment biosynthesis (16,20) and PpsR has been shown to suppress photopigment biosynthesis (21,22), we decided to test the effect of PpsR on puc::lacZ expression in Paracoccus denitrificans ATCC 17741, a nonphotosynthetic bacterium related to R. sphaeroides. When the ppsR gene on pPNs was introduced into strain ATCC 17741(pCF200Km), ␤-galactosidase activity decreased from 5,575 U to as low as 145 U, i.e., parallel to what was observed in R. sphaeroides 2.4.1(pCF200Km).…”