Structure of the puf operon of the obligately aerobic, bacteriochlorophyll alpha-containing bacterium Roseobacter denitrificans OCh114 and its expression in a Rhodobacter capsulatus puf puc deletion mutant

Abstract

Roseobacter denitrificans (Erythrobacter species strain OCh114) synthesizes bacteriochlorophyll a (BChl) and the photosynthetic apparatus only in the presence of oxygen and is unable to carry out primary photosynthetic reactions and to grow photosynthetically under anoxic conditions. The puf operon of R. denitrificans has the same five genes in the same order as in many photosynthetic bacteria, i.e., pufBALMC. PufC, the tetraheme subunit of the reaction center (RC), consists of 352 amino acids (M r , 39,043); 20 and 34% of the total amino acids are identical to those of PufC of Chloroflexus aurantiacus and Rubrivivax gelatinosus, respectively. The N-terminal hydrophobic domain is probably responsible for anchoring the subunit in the membrane. Four heme-binding domains are homologous to those of PufC in several purple bacteria. Sequences similar to pufQ and pufX of Rhodobacter capsulatus were not detected on the chromosome of R. denitrificans. The puf operon of R. denitrificans was expressed in trans in Escherichia coli, and all gene products were synthesized. The Roseobacter puf operon was also expressed in R. capsulatus CK11, a puf puc double-deletion mutant. For the first time, an RC/light-harvesting complex I core complex was heterologously synthesized. The strongest expression of the R. denitrificans puf operon was observed under the control of the R. capsulatus puf promoter, in the presence of pufQ and pufX and in the absence of pufC. Charge recombination between the primary donor P ؉ and the primary ubiquinone Q A ؊ was observed in the transconjugant, showing that the M and L subunits of the RC were correctly assembled. The transconjugants did not grow photosynthetically under anoxic conditions.

Carbohydrate Metabolism and Carbon Fixation in Roseobacter denitrificans OCh114

“…Here, we report studies of three carbon sources: pyruvate, D-glucose, and CO 2 (or HCO 3 − ). Spectral features of the photosynthesis system and light-harvesting complexes for the cultures grown in the minimal medium containing pyruvate or glucose are similar to the cultures grown in the rich medium (Figure 1a and 1b) as well as the results reported previously [13], [16]. The image of R. denitrificans cells grown in the minimal medium with pyruvate was examined by OLYMPUS FV1000/BX61 high-resolution confocal microscope, and the morphology and average cell size is consistent with previous reports [13].…”

Roseateles depolymerans gen. nov., sp. nov., a new bacteriochlorophyll a-containing obligate aerobe belonging to the β-subclass of the Proteobacteria

“…These organisms are referred to as aerobic photosynthetic bacteria (Harashima et al, 1982;Shiba, 1989;Shimada, 1995). Although the function of their photosynthetic apparatus has not yet been clarified, light-stimulated growth (Harashima et al, 1987;Yurkov & Gemerden, 1993) and photosynthetic activity (Harashima et al, 1982 ;Kortluke et al, 1997;Okamura et al, 1986;Shiba, 1984;Takamiya & Okamura, 1984) have been reported in some species of aerobic photosynthetic bacteria. Yurkov & Gemerden (1993) hypothesized an advantage of having both photosynthetic and heterotrophic metabolisms in terms of adaptation to the environment with altering light/dark conditions under aerobic T. Suyama and others conditions.…”

Photosynthetic Apparatus in Roseateles depolymerans 61A Is Transcriptionally Induced by Carbon Limitation

“…The subunits of the LH1 complex and most of the subunits of the RC complex are encoded by a gene cluster called the puf operon. The structures of the puf operon and the puf gene products in aerobic phototrophic bacteria have been studied well only for R. denitrificans (20) and Acidiphilium rubrum (23). It has been reported that the photosynthesis genes in these species are quite similar to those in the other phototrophic species.…”