Modestobacter lacusdianchii sp. nov., a Phosphate-Solubilizing Actinobacterium with Ability to Promote Microcystis Growth

Abstract

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.

Fig 1. Neighbour-joining phylogenetic tree based on 16S rRNA gene sequences of strain JXJ CY 19^T and representative type strains of the family Geodermatophilaceae.

Bootstrap values (expressed as percentages of 1,000 replications) of above 50% are shown at the nodes. Asterisks indicate clades that were conserved using the maximum-parsimony and maximum-likelihood methods. Bar, 0.005 sequence divergence.

Fig 2

Available phosphorus concentrations of different co-cultures of M. aeruginosa with strain JXJ CY 19^T in modified HGZ media on day 7 (A) and 60 (B). a, b, c, and d represented the treatments of initial bacterial cell densities of 0×10⁷ CFU/ml, 0.2×10⁷ CFU/ml, 1×10⁷ CFU/ml and 5×10⁷ CFU/ml respectively. Statistical comparisons with the control were made using ANOVA (* P < 0.05, ** P < 0.01).