Glutamate catabolism of Rickettsia rickettsi and factors affecting retention of metabolic activity

Abstract

Glutamate catabolism and the factors contributing to metabolic stability of purified suspensions of Rickettsia rickettsi were investigated. By use of (14)C-glutamate, it was shown that CO(2) was produced from all carbons of glutamate and that (14)CO(2) production was reduced by the addition of most of the unlabeled intermediates of the citric acid cycle and pyruvate. Oxalacetate, added in various concentrations, did not stimulate glutamate utilization. When the cells were suspended in bovine plasma albumin (BPA), CO(2) production from glutamate proceeded at a nearly uniform rate for 8 hr at 32 C and for 24 hr at 15 C. When BPA was used, the cells retained their metabolic activity at 0 or 30 C regardless of cell concentration, and were not influenced by the addition of varoius metabolites. Without BPA, metabolic stability was directly related to concentration. Of the stabilizers tested on low concentrations of rickettsiae, reduced glutathione was the most effective, provided that the gas phase contained predominantly N(2). Under these conditions of low partial pressure of O(2), glutamate further stabilized metabolic activity and was actively metabolized. The cells were also stabilized by oxidized glutathione in a gas phase of air, but under these conditions glutamate was utilized at a more moderate rate and it impaired metabolic stability.