Biochemical genetics revisited: the use of mutants to study carbon and nitrogen metabolism in the photosynthetic bacteria

Abstract

The biochemical genetics approach is defined as the use of mutants, in comparative studies with the wild‐type, to obtain information about biochemical and physiological processes in complex metabolic systems. This approach has been used extensively, for example in studies on the bioenergetics of the photosynthetic bacteria, but has been applied less frequently to studies of intermediary carbon and nitrogen metabolism in phototrophic organisms. Several important processes in photosynthetic bacteria—the regulation of nitrogenase synthesis and activity, the control of intracellular redox balance during photoheterotrophic growth, and chemotaxis—have been shown to involve metabolism. However, current understanding of carbon and nitrogen metabolism in these organisms is insufficient to allow a complete understanding of these phenomena. The purpose of the present review is to give an overview of carbon and nitrogen metabolism in the photosynthetic bacteria, with particular emphasis on work carried out with mutants, and to indicate areas in which the biochemical genetics approach could be applied successfully. In particular, it will be argued that, in the case of Rhodobacter capsulatus and Rb. sphaeroides, two species which are fast‐growing, possess a versatile metabolism, and have been extensively studied genetically, it should be possible to obtain a complete, integrated description of carbon and nitrogen metabolism, and to undertake a qualitative and quantitative analysis of the flow of carbon and reducing equivalents during photoheterotrophic growth. This would require a systematic biochemical genetic study employing techniques such as HPLC, NMR, and mass spectrometry, which are briefly discussed. The review is concerned mainly with Rb. capsulatus and Rb. sphaeroides, since most studies with mutants have been carried out with these organisms. However, where possible, a comparison is made with other species of purple non‐sulphur bacteria and with purple and green sulphur bacteria, and recent literature relevant to these organisms has been cited.

Accumulation of poly-β-hydroxybutyrate byRhodobacter sphaeroideson various carbon and nitrogen substrates

“…1–3b). This physiological restriction conforms to the finding that R. sphaeroides , as well as R. rubrum , lacks a glyoxylate bypass [14, 15]. The infeasibility to assimilate acetate may lead to predominant transformation of excess reductant coming from the non‐metabolized carbon substrate to PHB.…”

Enzymology of Nad + Synthesis

“…Willison and Tissot (1 994) have shown that the previously identified and sequenced essential gene efg (essential for growth) of E. coli (Allibert et al, 1987) and the adgA gene from Rhodobacter capsulatus (Willison, 1993) actually code for ammonia-dependent NAD+ synthetase and should therefore be redesignated nadE. The E. coli gene product, ORFl, has been overexpressed and characterized (Allibert et al, 1987); the recombinant enzyme protein is a dimer with a subunit molecular weight of 36,500, as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), which is higher than the value of 30,653 predicted from the nucleotide sequence; this discrepancy has been interpreted as an overestimation in SDS-PAGe attributable to the acidic nature of the protein (Allibert et al, 1987).…”

“…The Rb. capsulatus adgA enzyme gene potentially codes for a 59,7 1244, protein, as deduced from the nucleotide sequence (Willison, 1993). The B. subtilis NAD+ synthetase gene, known as the outB gene, has been also identified (Nessi, 1995).…”

“…This gene had been already cloned and sequenced by the same Authors (Albertini et al, 1987) and shown to be highly homologous to the E. coli gene (Albertini and Galizzi, 1990) and to a lesser extent to the Rb. capsulatus adgA gene and to the E. coli GuaA gene coding for GMP synthase (Willison, 1993).…”

Molecular ecology of a facultative swine waste lagoon

“…2003). Unlike PSB, which are essentially photoautotrophs with limited capabilities in organotrophic metabolism, the PNSB exhibit photoheterotrophy using a wide range of carbon metabolites, including volatile fatty acids (Willison 1993; McEwan 1994). However, many species of these bacteria are also capable of sulfide oxidation, although they cannot tolerate high concentrations of hydrogen sulfide (Thiele 1968; van Gemerden 1993; Blankenship et al.…”