The outer membrane of Gram-negative bacteria is an asymmetric lipid bilayer consisting of an essential glycolipid lipopolysaccharide (LPS) in its outer leaflet and phospholipids in the inner leaflet. Here, we show that yciM, a gene encoding a tetratricopeptide repeat protein of unknown function, modulates LPS levels by negatively regulating the biosynthesis of lipid A, an essential constituent of LPS. Inactivation of yciM resulted in high LPS levels and cell death in Escherichia coli; recessive mutations in lpxA, lpxC or lpxD that lower the synthesis of lipid A, or a gain of function mutation in fabZ that increases the formation of membrane phospholipids, alleviated the yciM mutant phenotypes. A modest increase in YciM led to significant reduction of LPS and increased sensitivity to hydrophobic antibiotics. YciM was shown to regulate LPS by altering LpxC, an enzyme that catalyses the first committed step of lipid A biosynthesis. Regulation of LpxC by YciM was contingent on the presence of FtsH, an essential membrane-anchored protease known to degrade LpxC, suggesting that FtsH and YciM act in concert to regulate synthesis of lipid A. In summary, this study demonstrates an essential role for YciM in regulation of LPS biosynthesis in E. coli.

Culture supernatants of Rhodobacter sphaeroides OU5 grown in the presence of 2-aminobenzoate gave an orange-red color-reaction with Salper's reagent, suggesting the presence of an indole derivative. This production was light-dependent and inducible only with 2-aminobenzoate. Replacement of 2-aminobenzoate with other 2-substituted benzoates did not result in the formation of indole. Fumarate appeared to be the conjugating molecule with 2-aminobenzoate, resulting in the formation of an indole derivative. The purified indole derivative was orange-brown in color, with a yields 0.34 mM from 1 mM 2-aminobenzoate. Infrared analysis suggested an indole ester and (1)H NMR analysis indicated an indole carboxylate, esterified with a terpenoid alcohol. The indole ester has a mass of 441 with the molecular formula C(27)H(39)NO(4). The IUPAC name of the compound is (3 E,5 E)-14-hydroxy-3,7,11-trimethyl-3,5-tetradecadienyl 2-(hydroxymethyl)-1 H-indole-3-carboxylate; and the common name given to this compound is sphestrin.

A new phytohormone was isolated as a metabolite of anthranilate photobiotransformation by Rhodobacter sphaeroides OU5. It was identified by MS and NMR ((1)H, (13)C) as an indole terpenoid ester [(2E,4E,6E,8E,10E,12E,14E,16E,18E)24-hydroxy-2,6,10,14,19 pentamethyl tetrecosa-2,4,6,8,10,12,14,16,18 nonenyl-2(hydroxy methyl)-1H-indole-3-carboxylate] and is named as rhodestrin. Rhodestrin at 50 nM: gave positive test in auxin bioassay and initiated more profuse and early rooting in tissue-cultured plants than other auxins at 5 microM.

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