Differences in chemical composition between nonflocculated and flocculated Azospirillum brasilense Cd

Abstract

A two-step broth replacement method was used to induce Azospirillum brasilense Cd bacteria to flocculate in vitro. Nonflocculated and flocculated cells were compared with regard to total cellular lipid composition, fatty acid profiles, and poly-beta-hydroxybutyrate (PHB), protein, and carbohydrate contents. The fatty acid profiles of nonflocculated and flocculated cells were qualitatively identical. Two unsaturated fatty acids, octadecanoate (18:1 cis-9) and hexadecanoate (16:1 cis-9), accounted for approximately 80% of the total fatty acid content in both phenotypes. The major lipids in nonflocculated and flocculated A. brasilense Cd cells were phosphatidylethanolamine, phosphatidylglycerol, and phosphatidylcholine. The process of flocculation also resulted in the synthesis de novo of a glycolipid and cardiolipin. Flocculation also resulted in a decrease in total cellular protein and lipid content and a proportional increase in total cellular PHB and carbohydrate content. Results indicated that the two-step broth replacement procedure was an effective means for the in vitro production of the stress-tolerant A. brasilense Cd cells with high PHB contents, which are desirable in commercial agricultural inocula. The PHB content of flocculated cells reached 60-65% of cell dry weight.Key words: Azospirillum, flocculation, poly-beta-hydroxybutyrate, PHB, lipid, protein, carbohydrate, fatty acid.