Requirement for Sodium in the Anaerobic Growth of Aerobacter aerogenes on Citrate

Abstract

Anaerobic growth of Aerobacter aerogenes on citrate as a carbon source required the presence of Na+. The growth rate increased with increasing Na+ concentration and was optimal at 0.10 M Na+. The requirement was specific for Na+, which could not be replaced by K+, NH4+, Li+, Rb+, or Cs+. K+ was required for growth in the presence of Na+, the optimal K+ concentration being 0.15 mm. Enzyme profiles were determined on cells grown in three different media: (i) intermediate Na+, high K+ concentration, (ii) high Na+, high K+ concentration, and (c) high Na+, low K+ concentration. All cells contained the enzymes of the citrate fermentation pathway, namely, citritase and the Na+-requiring oxalacetate (OAA) decarboxylase. All of the enzymes of the citric acid cycle were present, except a-ketoglutarate dehydrogenase which could not be detected. The incomplete citric acid cycle was, in effect, converted into two biosynthetic pathways leading to glutamate and succinate, respectively. The specific activities of citritase and OAA decarboxylase were lowest in medium (i), and under these conditions the activity of OAA decarboxylase appeared to be limited in vivo by the availability of Na+. Failure of A. aerogenes to grow anaerobically on citrate in the absence of Na+ can be explained at the enzymatic level by the Na+ requirement of the OAA decarboxylase step of the citrate fermentation pathway and by the absence of an alternate pathway of citrate catabolism.

NADH formation by Na+‐coupled reversed electron transfer in Klebsiella pneumoniae

“…The amount of NAD(P)H produced from citrate oxidation is probably insufficient to meet the biosynthetic demands, because 2-oxoglutarate dehydrogenase is repressed under anaerobic conditions (O'Brien and Stern, 1969) and succinate is not formed as fermentation product (see above).…”

Evolution of the citric acid cycle and respiratory energy conversion in prokaryotes

“…In regard to the effects of O 2, it is of considerable interest that regulation of KGD synthesis shows features in common with the controls affecting succinate~ fumarate interconversions. Thus, in amphiaerobes, KGD synthesis appears to be induced by O 2 and is repressed during anaerobic growth [30][31][32]. Keevil et al [33] have recently reported that even trace concentrations of 02 (approx.…”

Citrate metabolism in anaerobic bacteria

“…In E. aerogenes and K. pneumoniae citrate can serve as the sole source of carbon and energy only in the presence of Na + under anaerobic conditions. Hence, Na + is essential for the anaerobic growth of these bacteria on citrate [89,100,101]. In the presence of citrate, citrate lyase and oxaloacetate decarboxylase are induced and the tricarboxylic acid cycle is turned off [102].…”

“…Oxaloacetate is, therefore, decarboxylated to pyruvate by oxaloacetate decarboxylase whose activity is Na+-dependent [103]. Oxaloacetate is then converted to acetyl-CoA via pyruvate formate lyase [9,89]. Acetyl-CoA functions as a source for the generation of reducing power and ATP.…”

“…It has also been demonstrated that this enzyme in K. pneumoniae functions as an electrogenic Na + pump catalyzing the transport of 2 mol Na+/mol oxaloacetate from the inside to the outside, thus providing the organism with an additional source of energy [100,101]; Li + is also cotransported with citrate [105]. Under limited aerated conditions Na + also plays an important role in citrate metabolism in E. aerogenes and K. pneumoniae [89]. Under these conditions citrate is metabolized via the reactions of the tricarboxylic acid cycle and fermentation pathway.…”