No abstract

An actinomycete, isolated as a contaminant of a culture medium containing 25% NaCl, has been classified as Actinopolyspora halophila gen. et sp. nov. in the family Nocardiaceae. The morphology and biochemical characteristics of this organism distinguish it from other members of the family Nocardiaceae and other genera possessing a type IV cell wall. It requires high NaCl concentrations for growth and can grow in saturated NaCl. The lowest concentration permitting growth in liquid medium is 12%, and on solid medium, 10%. Colonies developing at lower salt concentrations contain holes resembling viral plaques. No growth occurred in a medium containing 30% KCl instead of NaCl. This organism can grow in simple media with NH4+ salts as nitrogen source and different sugars and other compounds as carbon source. Though it has a salt requirement almost as great as the extremely halophilic rods and cocci, it differs from these in containing diaminopimelic acid and in sensitivity to lysozyme; both properties suggest that it has a mucopeptide cell wall. It also contains some phospholipids common to other actinomycetes, but does not contain any phytanyl ether linked lipids characteristic of other extremely halophilic bacteria.

Pathways for biosynthesis of phosphatidylserine (PS), phosphatidylethanolamine (PE), and phosphatidylcholine (PC), in spinach leaves have been studied both in vivo (whole leaves and leaf slices) and in vitro (cell-free leaf fractions). Biosynthesis of PS was shown to occur by the action of a particle-bound CDP-diglyceride: serine phosphatidyltransferase, and PE by the action of a PS-decarboxylase localized in the 100 000 × g supernatant fraction. PE was also formed by the operation of the CDP-ethanolamine:diglyceride phosphorylethanolamine transferase, localized in the microsomal fraction. The presence of ethanolamine kinase required for formation of phosphorylethanolamine was demonstrated in vitro, but not the presence of CTP:phosphorylethanolamine cytidyltransferase; however, the latter is presumed present on the basis of in vivo results. Operation of the methylation pathway for biosynthesis of PC was established in vivo, and direct methylation of phosphatidyl-N-methylethanolamine to phosphatidyl-N,N-dimethylethanolamine (PE-diMe) and of PE-diME to PC by S-adenosylmethionine was demonstrated with a particulate enzyme system localized in the microsomal fraction; direct methylation of PE itself could not be shown in this system. PC was also synthesized by the CDP-choline:diglyceride phosphorylcholine transferase system localized in the microsomal fraction. Synthesis of PE and PC by Ca2+-stimulated exchange reactions with ethanolamine and choline, respectively, could be demonstrated, but at low rates. However, no synthesis of PS by exchange reactions with serine could be detected.

No abstract