Enzymes of the Entner-Doudoroff and pyruvate decarboxylation pathways in Zymomonas mobilis wild-type CP4 and mutant strains grown in continuous culture

Abstract

The osmotolerant Zymomonas mobilis strain suc₄₀, (containing plasmid pDS3154-inaZ), which is capable of producingsimultaneously ethanol and ice nuclei protein, was cultivated in a chemically defined complete sucrosemedium, as well as in a sugar beet molasses medium in continuous culture. The strain exhibited the normalMonod's relationship between biomass and dilution rate, and between growth substrate concentration and dilutionrate. Specific activities of a number of enzymes that appear to control important steps in the metabolic flux ofthe Entner-Doudoroff and pyruvate decarboxylation pathways were investigated over a range of growth ratesin steady state cultures. With the exception of glucose-6-phosphate dehydrogenase and gluconate kinase, all ofthe enzymes exhibited a very similar pattern for the wild type Z. mobilis CP4 and for the osmotolerant mutants,independent of the media used; the enzyme patterns remained relatively constant over the studied growth range.The specific activity of glucose-6-phosphate dehydrogenase was increased 2-fold by decreasing dilution rate insugar beet molasses. The specific activity of gluconate kinase was 2-fold lower at medium growth rates comparedwith that at either low or high growth rates. Pyruvate kinase, pyruvate decarboxylase and alcohol dehydrogenaseactivities were significantly higher compared with those of the enzymes governing the early steps of the Entner-Doudoroff pathway. The present study, which was designed to determine the behaviour of important enzymes insucrosemetabolismof Z. mobilis suc40/pDS3154-inaZ grown in continuous culture showed that the microorganismrequired regulation of specific enzyme activities at the transcriptional level when sugar beet molasses were used asthe growth medium.