The puhE gene of Rhodobacter capsulatus is needed for optimal transition from aerobic to photosynthetic growth and encodes a putative negative modulator of bacteriochlorophyll production.
A conserved orf of previously unknown function (herein designated as puhE) is located 3' of the reaction centre H (puhA) gene in purple photosynthetic bacteria, in the order puhABCE in Rhodobacter capsulatus. Disruptions of R. capsulatus puhE resulted in a long lag in the growth of photosynthetic cultures inoculated with cells grown under high aeration, and increased the level of the peripheral antenna, light-harvesting complex 2 (LH2). The amount of the photosynthetic reaction centre (RC) and its core antenna, light-harvesting complex 1 (LH1), was reduced; however, there was no decrease in expression of a lacZ reporter fused to the puf (RC and LH1) promoter, in RC assembly in the absence of LH1, or in LH1 assembly in the absence of the RC. In strains that lack LH2, disruption of puhE increased the in vivo absorption at 780 nm, which we attribute to excess bacteriochlorophyll a (BChl) pigment production. This effect was seen in the presence and absence of PufQ, a protein that stimulates BChl biosynthesis. Expression of puhE from a plasmid reduced A(780) production in puhE mutants. We suggest that PuhE modulates BChl biosynthesis independently of PufQ, and that the presence of excess BChl in PuhE(-)LH2(+) strains results in excess LH2 assembly and also interferes with the adaptation of cells during the transition from aerobic respiratory to anaerobic photosynthetic growth.
Aklujkar
Muktak
M
Department of Microbiology and Immunology, University of British Columbia, 300-6174 University Blvd., Vancouver, BC, Canada V6T 1Z3.
Prince
Roger C
RC
Beatty
J Thomas
JT
D000332:Aerobiosis / Q000235:genetics; D000693:Anaerobiosis / Q000235:genetics; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D001429:Bacteriochlorophylls / Q000096:biosynthesis*; D019069:Cell Respiration / Q000235:genetics; D017353:Gene Deletion; D015964:Gene Expression Regulation, Bacterial; D005798:Genes, Bacterial / Q000235:genetics; D045342:Light-Harvesting Protein Complexes / Q000378:metabolism; D010788:Photosynthesis / Q000235:genetics; D045322:Photosynthetic Reaction Center Complex Proteins / Q000235:genetics / Q000378:metabolism; D016354:Rhodobacter capsulatus / Q000235:genetics* / Q000378:metabolism*; D013057:Spectrum Analysis; D013696:Temperature; D013997:Time Factors
D001426:Bacterial Proteins; D001429:Bacteriochlorophylls; D045342:Light-Harvesting Protein Complexes; D045322:Photosynthetic Reaction Center Complex Proteins; C087270:PufQ protein, Rhodobacter capsulatus