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A novel actinobacterium, designated strain JXJ CY 19T, was isolated from a culture mat of Microcystis aeruginosa FACHB-905 collected from Dianchi Lake, South-west China. 16S rRNA gene sequences comparison of strain JXJ CY 19T and the available sequences in the GenBank database showed that the strain was closely related to Modestobacter marinus 42H12-1T (99.1% similarity) and Modestobacter roseus KLBMP 1279T (99.0%). The isolate had meso-diaminopimelic in the cell wall with whole-cell sugars of mannose, rhamnose, ribose, glucose, galactose, and arabinose. The menaquinone detected was MK-9(H4), while the major cellular fatty acids include C17:1 ω8c, C15:0 iso, C15:1 iso G and C16:0 iso. The polar lipids were diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylinositol, phosphatidylinositol mannoside and an unidentified phospholipid. The DNA-DNA hybridization values between strains JXJ CY 19T and the closely related type strains Modestobacter marinus CGMCC 4.5581T and Modestobacter roseus NBRC 108673T were determined to be 50.8 ± 0.8% and 44.1 ± 1.7%, respectively. The DNA G+C content was 71.9 mol%. On the basis of the above taxonomic data and differences in physiological characters from the closely related type strains, strain JXJ CY 19T was recognized as a novel species of the genus Modestobacter, for which the name Modestobacter lacusdianchii sp. nov. (JXJ CY 19T = KCTC 39600T = CPCC 204352T) is proposed. The type strain JXJ CY 19T can solubilize calcium phosphate tribasic (Ca3(PO4)2), phytin and L-α-phosphatidylcholine. The phosphate-solubilizing property of the novel actinobacterium could be a possible factor for the increase in growth of Microcystis aeruginosa FACHB-905 in ecosystem where the amount of available soluble phosphate is limited such as Dianchi Lake. [ABSTRACT FROM AUTHOR]

ArgR, a transcriptional regulator belonging to the AraC/XylS family, plays a key role in arginine metabolism regulation. ArgR has also been found to repress the transcription of a lipase gene, but its molecular mechanism is still unknown. In this study, we investigated the molecular mechanism acting on the expression of intracellular lipase gene lipA regulated by ArgR in Pseudomonas protegens Pf-5 through knockout and overexpression of argR , detection of DNA-protein interaction in vivo , determining whole-cell lipase activities of various strains derived from Pf-5, and examining β-galactosidase activities of various lacZ fusions. The results demonstrated that ArgR inhibits lipA expression at the transcriptional level. Further results showed that the inhibition of lipA transcription by ArgR is mediated by binding to the ArgR binding site of lipA promoter to produce steric hindrance, in which the common sequence, TGTCGC is crucial for the ArgR binding. Besides, arginine inhibits lipA expression in both wild-type and argR mutant, and shows a synergistic inhibition on lipA expression when combined with ArgR. To the best of our knowledge, this is the first report on ArgR directly repressing the transcription of a lipase gene. • ArgR directly inhibits lipA transcription by binding to lipA promoter. • lipA promoter includes an ArgR binding site bound by ArgR. • Arginine represses lipA expression in both wild-type and argR knockout mutant. [ABSTRACT FROM AUTHOR]