Lipid metabolism during encystment of Azotobacter vinelandii

Abstract

The formation of cysts by Azotobacter vinelandii involves the synthesis of lipids as major metabolic products. Cells which encyst at low levels in aging glucose cultures undergo the same pattern of lipid synthesis as cells which undergo reasonably synchronous encystment in beta-hydroxybutyrate or n-butanol. The accumulation of poly-beta-hydroxybutyrate (PHB) precedes the synthesis of 5-n-heneicosylresorcinol and 5-n-tricosylresorcinol (AR1), which is then followed in about 6 h by the synthesis of the 5-n-alkylresorcinol galactosides (AR2). In the mature cyst, PHB, AR1, and AR2 account for 8, 5.6, and 4.5%, respectively, of the dry weight. Phospholipid formation levels off 4 h postinduction, which coincides with the final cell division, but fatty acids synthesis continues at a very low level throughout encystment, suggesting some turnover of fatty acid. Distribution studies show that AR1 and AR2 are found in roughly equal amounts in the exine and central body of the cysts, with only trace amounts recovered from the intine. Studies of cysts labeled during encystment with [14C]beta-hydroxybutyrate or during vegetative growth with [14C]glucose suggest that the exine structure is synthesized during encystment, but that the intine is composed largely of vegetative cell components.