Chie Koseki

Identification of succinate exporter in Corynebacterium glutamicum and its physiological roles under anaerobic conditions.

Corynebacterium glutamicum produces succinate from glucose via the reductive tricarboxylic acid cycle under microaerobic and anaerobic conditions. We identified a NCgl2130 gene of C. glutamicum as a novel succinate exporter that functions in succinate production, and designated sucE1. sucE1 expression levels were higher under microaerobic conditions than aerobic conditions, and overexpression or disruption of sucE1 respectively increased or decreased succinate productivity during fermentation. Under microaerobic conditions, the sucE1 disruptant sucE1Δ showed 30% less succinate productivity and a lower sugar-consumption rate than the parental strain. Under anaerobic conditions, succinate production by sucE1Δ ceased. The intracellular succinate and fructose-1,6-bisphosphate levels of sucE1Δ under microaerobic conditions were respectively 1.7-fold and 1.6-fold higher than those of the parental strain, suggesting that loss of SucE1 function caused a failure of succinate removal from the cells, leading to intracellular accumulation that inhibited upstream sugar metabolism. Homology and transmembrane helix searches identified SucE1 as a membrane protein belonging to the aspartate:alanine exchanger (AAE) family. Partially purified 6x-histidine-tagged SucE1 (SucE1-[His](6)) reconstituted in succinate-loaded liposomes clearly demonstrated counterflow and self-exchange activities for succinate. Together, these findings suggest that sucE1 encodes a novel succinate exporter that is induced under microaerobic conditions, and is important for succinate production under both microaerobic and anaerobic conditions.

Improved Production of Enzymes, Which Are Expressed under the Pho Regulon Promoter, in the rmf Gene (encoding ribosome modulation factor) Disruptant of Escherichia coli

Using a DNA macroarray, we investigated the effects of rmf gene (encoding ribosome modulation factor) disruption on gene expression profiles in Escherichia coli. This strain showed a phosphate-starvation-like response in gene expression even under phosphate sufficient conditions; significant upregulation of the Pho regulon genes was observed. Further, the production of alkaline phosphatase, a product of the Pho regulon gene, phoA, increased in the rmf disruptant under a Pi sufficient condition. Furthermore, production of PhoC acid phosphatase/nucleoside pyrophosphate phosphotransferase derived from Morganella morganii also increased significantly in the rmf disruptant. We concluded that host modification by the rmf gene disruption has potential benefit in industrial enzyme production using Escherichia coli.

Analysis of strain-specific genes in glutamic acid-producing Corynebacterium glutamicum ssp. lactofermentum AJ 1511

Strains of the bacterium, Corynebacterium glutamicum, are widely used for the industrial production of L-glutamic acid and various other substances. C. glutamicum ssp. lactofermentum AJ 1511, formerly classified as Brevibacterium lactofermentum, and the closely related C. glutamicum ATCC 13032 have been used as industrial strains for more than 50 years. We determined the whole genome sequence of C. glutamicum AJ 1511 and performed genome-wide comparative analysis with C. glutamicum ATCC 13032 to determine strain-specific genetic differences. This analysis revealed that the genomes of the two industrial strains are highly similar despite the phenotypic differences between the two strains. Both strains harbored unique genes but gene transpositions or inversions were not observed. The largest unique region, a 220-kb AT-rich region located between 1.78 and 2.00 Mb position in C. glutamicum ATCC 13032 genome, was missing in the genome of C. glutamicum AJ 1511. The next two largest unique regions were present in C. glutamicum AJ 1511. The first region (413-484 kb position) contains several predicted transport proteins, enzymes involved in sugar metabolism, and transposases. The second region (1.47-1.50 Mb position) encodes restriction modification systems. A gene predicted to encode NADH-dependent glutamate dehydrogenase, which is involved in L-glutamate biosynthesis, is present in C. glutamicum AJ 1511. Strain-specific genes identified in this study are likely to govern phenotypes unique to each strain.