Journal Article

glyoxylate shunt is essential for CO2-requiring oligotrophic growth of Rhodococcus erythropolis N9T-4

Wakamatsu, Miki, Takagi, Hiroshi, Yu, Fujio, Yano, Takanori, Yoshida, Nobuyuki

2015

Overview

Rhodococcus erythropolis N9T-4 shows extremely oligotrophic growth requiring atmospheric CO₂ and forms its colonies on an inorganic basal medium (BM) without any additional carbon source. Screening of a random mutation library constructed by a unique genome deletion method that we established indicated that the aceA, aceB, and pckG genes encoding isocitrate lyase, malate synthase, and phosphoenolpyruvate carboxykinase, respectively, were requisite for survival on BM plates. The aceA- and aceB deletion mutants and the pckG deletion mutant grew well on BM plates containing L-malate and D-glucose, respectively, suggesting that the glyoxylate (GO) shunt and gluconeogenesis are essential for the oligotrophic growth of N9T-4. Interestingly, most of the enzyme activities in the TCA cycle were observed in the cell-free extract of N9T-4, with perhaps the most important exception being α-ketoglutarate dehydrogenase (KGDH) activity. Instead of the KGDH activity, we detected a remarkable level of α-ketoglutarate decarboxylase (KGD) activity, which is the activity exhibited by the E1 component of the KGDH complex in Mycobacterium tuberculosis. The recombinant KGD of N9T-4 catalyzed the decarboxylation of α-ketoglutarate to form succinic semialdehyde (SSA) in a time-dependent manner. Since N9T-4 also showed a detectable SSA dehydrogenase activity, we concluded that N9T-4 possesses a variant TCA cycle, which uses SSA rather than succinyl-CoA. These results suggest that oligotrophic N9T-4 cells utilize the GO shunt to avoid the loss of carbons as CO₂ and to conserve CoA units in the TCA cycle.

• Publisher: Springer Berlin Heidelberg,Springer Nature B.V
• Subject: alpha-ketoglutaric acid / Applied Microbial and Cell Physiology / Biomedical and Life Sciences / Biotechnology / carbon / Carbon dioxide / Carbon Dioxide - metabolism / Carbon sources / culture media / Culture Media - chemistry / Decarboxylation / Dehydrogenase / Dehydrogenases / Deletion mutant / Enzymatic activity / enzyme activity / Gene deletion / genes / Genomes / Gluconeogenesis / Glucose / glyoxylate cycle / Glyoxylates - metabolism / Isocitrate lyase / Ketoglutaric acid / Life Sciences / Malate synthase / malates / Metabolic Networks and Pathways - genetics / Microbial Genetics and Genomics / Microbial Viability / Microbiology / Mutagenesis / Mutants / Mutation / Mycobacterium tuberculosis / Oxoglutarate dehydrogenase (lipoamide) / Plates / Rhodococcus / Rhodococcus - growth & development / Rhodococcus - metabolism / Rhodococcus erythropolis / screening / Succinyl-CoA / Tricarboxylic acid cycle / Tuberculosis