Screening and characterization of an Agrobacterium tumefaciens mutant strain producing high level of coenzyme Q₁₀

A mutant of Agrobacterium tumefaciens (S02-13) producing high levels of coenzyme Q₁₀ (CoQ₁₀), was selected by high-throughput screening after repeated NTG mutagenesis. Mutant S02-13 was resistant to sodium azide and menadione and showed an eight-fold increase in CoQ₁₀ production, as compared to that of the parent strain. The amount of CoQ₁₀ produced by this mutant reached 350 mg l^-1 in pH-stat fed-batch culture. Mutant S02-13 differed from wild-type in morphology, biochemical properties, and proteome profiles. Scanning electron microscopy results revealed a remarkable change in morphology: the wild-type strain had a rod shape, whereas the mutant S02-13 was coccoid. In contrast to wild-type, the mutant S02-13 strain showed a negative reaction to tryptophan deaminase and N₂ reduction, and a positive reaction to nitrate production in API kit assays. The spots representing proteins that were increased in the proteome expression of the mutant S02-13 strain were identified as glyceraldehyde-3-phosphate dehydrogenase (GAPDH), glucosaminitol dehydrogenase (GlcNOH), and superoxide dismutase (SOD). In particular, the enzyme activities of GAPDH and GlcNOH increased eight-fold and three-fold, respectively, in the mutant, as compared to the wild-type.