SECRETION OF POLY(3-HYDROXYBUTYRATE) DEPOLYMERASE BY ALCALIGENES-FAECALIS T1

The relationship between cell growth and the secretion of poly(3-hydroxybutyrate) (PHB) depolymerase by Alcaligenes faecalis T1, a gram-negative bacterium, was studied with various carbohydrates added to the medium as sole carbon sources. A. faecalis T1 could grow on many kinds of carbon sources, the growth rate depending on the carbon source species. However, among the various carbon sources tested, glucose, PHB and its metabolites, D(-)-3-hydroxybutyrate and acetoacetate, but not succinate or other carboxylic acids, caused the secretion of PHB depolymerase. In the medium containing glucose as a sole carbon source, A. faecalis T1 started to grow and to secrete PHB depolymerase after 60 h of cultivation. In contrast, the growth of cells in the medium containing succinate as a sole carbon source started within 2 h and reached a plateau level after 6 h of cultivation, but the cells did not secrete the enzyme into the culture medium. However, succinate-grown cells contained a considerable amount of PHB depolymerase, the level being the same as that in glucose-grown cells. Most of the cellular PHB depolymerase was found to be localized in the membrane fractions prepared from the glucose- and succinate-grown cells. In contrast to the glucose-grown cells, the succinate-grown cells exhibited no ability to incorporate [C-14]glucose, although the cells exhibited several glycolytic enzyme activities for glucose oxidation. Therefore, it seems that the glucose availability for this bacterium is dependent on the induction of some protein(s) essential for glucose uptake and that glucose metabolites such as ketone bodies are essential for PHB depolymerase secretion by A. faecalis T1.