The Effect of Growth Conditions on the Respiratory System of a Succinoglucan-producing Strain of Agrobacterium radiobacter

SUMMARY: The respiratory system of Agrobacterium radiobacter NCIB 11883, a producer of succinoglucan exopolysaccharide under ammonia-limited conditions, was studied following growth in continuous culture (D = 0·045 h-1)under glucose, oxygen and ammonia limitation. The respiratory chain contained b- and c-type cytochromes, plus two terminal oxidases (aa 3 and co) under all growth conditions, and exhibited a low transhydrogenase activity. An inactive apoenzyme form of the quinoprotein glucose dehydrogenase was also present which could be activated by adding pyrroloquinoline quinone (PQQ) to cell suspensions. The activity of the terminal region of the respiratory chain increased approximately fourfold following growth under oxygen limitation, and this was accompanied by a significant increase in the concentration of cytochrome oxidaseco. Whole cells exhibited →H+/O quotients of 5·5-6·3 for the oxidation of endogenous substrate depending on the nature of the growth-limiting nutrient. It is concluded that the respiratory chain energy conservation system of this organism is not significantly modified during ammonia-limited growth to offset the increased energy demands for exopolysaccharide synthesis.