Specific rates of substrate oxidation and product formation in autotrophically growingChromatium vinosum cultures

Abstract

Kinetics ofChromatium metabolism under autotrophic conditions were studied in batch culture. Description of various over-all metabolic rates in equal dimensions enabled direct comparison of such different processes as electron donor oxidation, storage-polymer synthesis, and growth. In the presence of sulfide, the specific rate of sulfur oxidation is partly depressed. Upon sulfide depletion, the latter rate showed an instantaneous increase of 22%. Simultaneously, glycogen was degraded. These two modifications fully compensate for the absence of sulfide, thus enabling growth to continue withμ _max (0.12 h^-1). These findings indicate that the potential rate of supply of electrons exceeds the biosynthetic demand for reducing power. The synthesis of glycogen in the presence of sulfide may be regarded overflow metabolism, assuming theμ _max is intrinsically limited at 0.12 h^-1. An alternative hypothesis is based on the assumption of an ineffective glycogen-synthesis regulation. Conceivably, growth and glycogen synthesis are competing for biosynthetic intermediates, the supply of which is limited by the maximum specific rate of e.g. the Calvin cycle. If so, both growth and glycogen synthesis are performed at submaximal rates. The rate of glycogen synthesis is greatly enhanced by the addition of growth inhibitors, and an increasedμ _max value is found in the presence of acetate. These two findings together are consistent with the second hypothesis.