Insights into growth kinetics and roles of enzymes of Krebs' cycle and sulfur oxidation during exochemolithoheterotrophic growth ofAchromobacter aegrifaciensNCCB 38021 on succinate with thiosulfate as the auxiliary electron donor

Achromobacter aegrifaciensNCCB 38021 was grown heterotrophically on succinateversusexochemolithoheterotrophically on succinate with thiosulfate as auxiliary electron donor. In batch culture, no significant differences in specific molar growth yield or specific growth rate were found for the two growth conditions, but in continuous culture in the succinate-limited chemostat, the maximum specific growth yield coefficient increased by 23.3% with thiosulfate present, consistent with previous studies of endo- and exochemolithoheterotrophs and thermodynamic predictions. Thiosulfate oxidation was coupled to respiration at cytochromec(551), and thiosulfate-dependent ATP biosynthesis occurred. Specific activities of cytochromec-linked thiosulfate dehydrogenase (E.C. 1.8.2.2) and two other enzymes of sulfur metabolism were significantly higher in exochemolithoheterotrophically grown cell extracts, while those of succinyl-transferring 2-oxoglutarate dehydrogenase (E.C. 1.2.4.2), fumarate hydratase (E.C. 4.2.1.2) and malate dehydrogenase (NAD(+), E.C. 1.1.1.37) were significantly lower-presumably owing to less need to generate reducing equivalents during Krebs' cycle, since they could be produced from thiosulfate oxidation.

Automated summary

The study demonstrated that Achromobacter aegrifaciens NCCB 38021 exhibited differences in growth characteristics under different growth conditions, with thiosulfate as an auxiliary electron donor significantly increasing growth rate. Thiosulfate oxidation was coupled to respiration at cytochrome c(551), leading to ATP generation.