Anaerobic fumarate transport in Escherichia coli by an fnr-dependent dicarboxylate uptake system which is different from the aerobic dicarboxylate uptake system

Abstract

Escherichia coli grown anaerobically with fumarate as electron acceptor is able to take up C4-dicarboxylates by a specific transport system. The system differs in all tested parameters from the known aerobic C4-dicarboxylate transporter. The anaerobic transport system shows higher transport rates (95 ,umol/g [dry weight] per min versus 30 ,umol/g/min) and higher Kms (400 versus 30 ,uM) for fumarate than for the aerobic system. Mutants lacking the aerobic dicarboxylate uptake system are able to grow anaerobically at the expense of fumarate respiration and transport dicarboxylates with wild-type rates after anaerobic but not after aerobic growth. Transport by the anaerobic system is stimulated by preloading the bacteria with dicarboxylates. The anaerobic transport system catalyzes homologous and heterologous antiport of dicarboxylates, whereas the aerobic system operates only in the unidirectional mode. The anaerobic antiport is measurable only in anaerobically grown bacteria withfinr' backgrounds. Additionally, the system is inhibited by incubation of resting bacteria with physiological electron acceptors such as 02, nitrate, dimethyl sulfoxide, and fumarate. The inhibition is reversed by the presence of reducing agents. It is suggested that the physiological role of the system is a fumarate/succinate antiport under conditions of fumarate respiration.

Menaquinone‐dependent succinate dehydrogenase of bacteria catalyzes reversed electron transport driven by the proton potential

“…B. subtilis accumulated succinate in a time-dependent manner and, after 5Ϫ10 min, maximal accumulation was achieved. The rates were typical for this bacterium [21], but lower than those measured previously for E. coli [17,19]. The uptake rates, in particular those for B. macerans, were distinctly lower than the succinate-oxidase activities (see Table 2).…”

“…Intracellular contents of labeled dicarboxylates were determined after silicone-oil centrifugation. For anaerobically grown cells, buffer A contained 1 mM dithiothreitol and was degassed as described by Engel et al [19]. For calculation of the dry mass of the bacterial cell suspensions it was assumed that A 578 ϭ 1 corresponds to 280 mg dry mass/l.…”

Secondary solute transport in bacteria

“…In addition to the excretion of galactose by lactose metabolizing S. thermophilus (Gal-) cells, excretion of monosaccharides is frequently observed during growth on disaccharides, e.g., lactose utilization in E. coli (Gal +) [91]; sucrose and lactose utilization in various lactic acid bacteria [20]. Evidence has also been presented for fumurate/ succinate exchange under conditions of fumarate respiration in E. coli [92]. Whether this system is a true antiporter that only catalyzes an exchange reaction or whether it can choose among alternative substrates, i.e., protons (sodium ions) or succinate, for fumarate uptake is unknown.…”

Identification of a third secondary carrier (DcuC) for anaerobic C4-dicarboxylate transport in Escherichia coli: roles of the three Dcu carriers in uptake and exchange

“…Under aerobic growth conditions, unidirectional uptake of C 4 dicarboxylates (fumarate, succinate, and malate) and aspartate, but no export, is catalyzed (5,12). This transport is effected by a binding protein-dependent carrier or by a secondary carrier which is driven by the electrochemical H ϩ gradient over the membrane (10,17).…”

“…The dctA gene has been sequenced (23), but none of the carriers has been clearly defined so far by genetic or biochemical means. Bacteria grown under anaerobic conditions, on the other hand, catalyze exchange, uptake, and efflux of C 4 dicarboxylates (5,6). Fumarate/succinate exchange is required during fumarate respiration where the acceptor fumarate has to be taken up and the product succinate has to be excreted.…”