Myxospore Coat Synthesis in Myxococcus xanthus : In Vivo Incorporation of Acetate and Glycine

Abstract

Myxospore coat synthesis in Myxococcus xanthus was studied by incorporation of [ 14 C]acetate into intermediates in the biosynthesis of coat polysaccharide and into acid-insoluble material during vegetative growth and after glycerol induction of myxospores. During short labeling periods at 27°C, the radioactivity was shown to be located primarily in N -acetyl groups rather than sugar moieties. Two hours after glycerol induction, the pools of N -acetylglucosamine 6-phosphate and uridine 5′-diphosphate- N -acetylgalactosamine (UDPGalNAc) plus uridine 5′-diphosphate- N -glucosamine increased about twofold and were labeled at twice the rate measured for vegetative cells. The increased rate of synthesis of UDPGalNAc and its precursors could be correlated with increased enzyme activities measured in vitro. Controlled acid hydrolysis revealed that the galactosamine portion of the myxospore coat was N -acetylated. After glycerol induction, the incorporation of acetate into acid-insoluble material increased threefold. This enhanced incorporation was sensitive to neither penicillin nor d -cycloserine. In contrast, bacitracin inhibited the incorporation of [ 14 C]acetate into acid-insoluble material more effectively 2 h after myxospore induction than during vegetative growth. Chloramphenicol added to cells 90 min after induction blocked further increase in the rate of [ 14 C]acetate incorporation. Since the myxospore coat contains glycine, polymer synthesis was also measured by chloramphenicol-insensitive [ 14 C]glycine incorporation into acid-insoluble material. Although protein synthesis decreased after glycerol induction, glycine incorporation increased. Two hours after induction, glycine incorporation was only 75% inhibited by chloramphenicol and rifampin. The chloramphenicol-insensitive rate of incorporation of [ 14 C]glycine increased during the first hour after myxospore induction and reached a peak rate after 2 to 3 h. The chloramphenicol-resistant incorporation of [ 14 C]glycine was resistant to penicillin but sensitive to bacitracin.