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Quorum sensing (QS) in Sinorhizobium meliloti, the N-fixing bacterial symbiont of Medicago host plants, involves at least half a dozen different N-acyl homoserine lactone (AHL) signals and perhaps an equal number of AHL receptors. The accumulation of 55 proteins was found to be dependent on SinI, the AHL synthase, and/or on ExpR, one of the AHL receptors. Gas chromatography-mass spectrometry and electrospray ionization tandem mass spectrometry identified 3-oxo-[C.sub.14]-homoserine lactone (3-oxo-[C.sub.14]-HSL), [C.sub.16]-HSL, 3-oxo[C.sub.16]-HSL, [C.sub.16:1]-HSL, and 3-oxo-[C.sub.16:1]-HSL as the sinI-dependent AHL QS signals accumulated by the 8530 exp[R.sup.[+ or -]] strain under the conditions used for proteome analysis. The 8530 exp[R.sup.[+ or -]] strain secretes additional, unidentified QS-active compounds. Addition of 200 nM [C.sub.14]-HSL or [C.sub.16:1]-HSL, two of the known SinI AHLs, affected the levels of 75% of the proteins, confirming that their accumulation is QS regulated. A number of the QS-regulated proteins have functions plausibly related to symbiotic interactions with the host, including ExpE6, IdhA, MocB, Gor, PckA, LeuC, and AglE. Seven of 10 single-crossover [beta]-glucuronidase (GUS) transcriptional reporters in genes corresponding to QS-regulated proteins showed significantly different activities in the sinI and expR mutant backgrounds and in response to added SinI AHLs. The sinI mutant and several of the single-crossover strains were significantly delayed in the ability to initiate nodules on the primary root of the host plant, Medicago truncatula, indicating that sinI-dependent QS regulation and QS-regulated proteins contribute importantly to the rate or efficiency of nodule initiation. The sinI and expR mutants were also defective in surface swarming motility. The sinI mutant was restored to normal swarming by 5 nM [C.sub.16:1]-HSL.

Research demonstrates that sinR/sinI locus generates many unique N-acyl homoserine lactones with acyl side chains ranging from 12 to 18 carbons. Data indicate that the synthesis of these long-chain lactones is dependent on sinI gene, whereas short-chain lactones are not affected. Disruption of the sin system delays the appearance of nitrogen-fixing nodules sugesting a role in quorum sensing.

The syntheses of three dimeric, 30-membered bislactone alkaloids, representing the three possible head-to-tail combinations of unsaturated polyazamacrolides from Subcoccinella vigintiquatuopunctata are described. The synthetic route for all the three alkaloids involves a common step of nucleophilic opening of a chiral aziridine.

To study the molecular basis for predator-prey coevolution, we investigated how Caenorhabditis elegans responds to the predatory fungus Arthrobotrys oligospora. C. elegans and other nematodes were attracted to volatile compounds produced by A. oligospora. Gas-chromatographic mass-spectral analyses of A. oligospora-derived volatile metabolites identified several odors mimicking food cues attractive to nematodes. One compound, methyl 3-methyl-2-butenoate (MMB) additionally triggered strong sex- and stage-specific attraction in several Caenorhabditis species. Furthermore, when MMB is present, it interferes with nematode mating, suggesting that MMB might mimic sex pheromone in Caenorhabditis species. Forward genetic screening suggests that multiple receptors are involved in sensing MMB. Response to fungal odors involves the olfactory neuron AWCs. Single-cell RNA-seq revealed the GPCRs expressed in AWC. We propose that A. oligospora likely evolved the means to use olfactory mimicry to attract its nematode prey through the olfactory neurons in C. elegans and related species. [ABSTRACT FROM AUTHOR]

Histamine is an inflammatory agent that contributes to bovine laminitis. Cattle fed silage-containing rations often have large populations ofAllisonella histaminiformans,but this obligate histidine-decarboxylating bacterium could not be isolated from cattle fed timothy hay. The growth ofA. histaminiformanswas stimulated by yeast extract, protein hydrolysates, and water-soluble extracts of alfalfa or corn silage. Extracts of alfalfa were more potent than corn silage. Because growth and histamine production were not stimulated by Casamino Acids or a mixture of purified amino acids, it appeared thatA. histaminiformansrequires peptides. The idea thatA. histaminiformansrequires peptides is consistent with the observation that alfalfa silages often have a large amount of peptide nitrogen. [ABSTRACT FROM AUTHOR]

Quorum sensing (QS) in Sinorhizobium meliloti, the N-fixing bacterial symbiont of Medicago host plants, involves at least half a dozen different N-acyl homoserine lactone (AHL) signals and perhaps an equal number of AHL receptors. The accumulation of 55 proteins was found to be dependent on SinI, the AHL synthase, and/or on ExpR, one of the AHL receptors. Gas chromatography-mass spectrometry and electrospray ionization tandem mass spectrometry identified 3-oxo-C14-homoserine lactone (3-oxo-C14-HSL), C16-HSL, 3-oxo-C16-HSL, C16:1-HSL, and 3-oxo-C16:1-HSL as the sinI-dependent AHL QS signals accumulated by the 8530 expR+ strain under the conditions used for proteome analysis. The 8530 expR+ strain secretes additional, unidentified QS-active compounds. Addition of 200 nM C14-HSL or C16.1-HSL, two of the known SinI AHLs, affected the levels of 75% of the proteins, confirming that their accumulation is QS regulated. A number of the QS-regulated proteins have functions plausibly related to symbiotic interactions with the host, including ExpE6, IdhA, MocB, Gor, PckA, LeuC, and AglE. Seven of 10 single-crossover β-glucuronidase (GUS) transcriptional reporters in genes corresponding to QS-regulated proteins showed significantly different activities in the sinI and expR mutant backgrounds and in response to added SinI AHLs. The sinI mutant and several of the single-crossover strains were significantly delayed in the ability to initiate nodules on the primary root of the host plant, Medicago truncatula, indicating that sinI-dependent QS regulation and QS-regulated proteins contribute importantly to the rate or efficiency of nodule initiation. The sinI and expR mutants were also defective in surface swarming motility. The sinI mutant was restored to normal swarming by 5 nM C16:1-HSL. [ABSTRACT FROM AUTHOR]