A Gram-stain-negative and rod-shaped bacterial strain, 12-OD1T, with rock phosphate solubilizing ability was isolated from agricultural soil in Hailun, Heilongjiang, PR China. The isolate was affiliated to the genus Massilia , based on 16S rRNA gene sequence alignments, having the highest similarities with Massilia putida 6 NM-7T (98.67 %), Massilia kyonggiensis TSA1T (98.28 %), and Massilia norwichensis NS9T (98.07 %), respectively. The DNA G+C content was 67.72 mol% and DNA–DNA hybridization showed low relatedness values (less than 47 %) between strain 12-OD1T and other phylogenetically related species of the genus Massilia . The predominant isoprenoid quinone was Q-8 and the polar lipid profile comprised diphosphatidylglycerol, phosphatidylglycerol and phosphatidylethanolamine. The major fatty acids were C17 : 0 cyclo (25.4 %), C16 : 0 (23.4 %) and summed feature 3 (C16 : 1ω7c and/or C16 : 1 ω6c) (22.5 %), which differentiates it from close relatives within the genus Massilia . Combined genetic, physiological and biochemical properties indicate that strain 12-OD1T is a novel species of the genus Massilia , for which the name Massilia phosphatilytica sp. nov., is proposed, with the type strain 12-OD1T (=CCTCC AB 2016251T=LMG 29956T=KCTC 52513T).

Inorganic phosphate solubilizing bacteria (iPSB) are essential to facilitate phosphorus (P) mobilization in alkaline soil, however, the phylogenetic structure of iPSB communities remains poorly characterized. Thus, we use a reference iPSB database to analyze the distribution of iPSB communities based on 16S rRNA gene illumina sequencing. Additionally, a noval pqqC primer was developed to quantify iPSB abundance. In our study, an alkaline soil with 27-year fertilization treatment was selected. The percentage of iPSB was 1.10~2.87% per sample, and the dominant iPSB genera were closely related to Arthrobacter, Bacillus, Brevibacterium and Streptomyces. Long-term P fertilization had no significant effect on the abundance of iPSB communities. Rather than P and potassium (K) additions, long-term nitrogen (N) fertilization decreased the iPSB abundance, which was validated by reduced relative abundance of pqqC gene (pqqC/16S). The decreased iPSB abundance was strongly related to pH decline and total N increase, revealing that the long-term N additions may cause pH decline and subsequent P releases relatively decreasing the demands of the iPSB community. The methodology and understanding obtained here provides insights into the ecology of inorganic P solubilizers and how to manipulate for better P use efficiency.

The ability to solubilize fixed inorganic phosphorus (P) for plant growth is important for increasing crop yield. More P can be released by inoculating soil with inorganic-phosphate-solubilizing bacteria (iPSBs). We used 96-well microplates instead of traditional 200-mm petri dishes to rapidly screen iPSB strains for their solubilizing ability. We simultaneously obtained 76 iPSB isolates from 576 wells containing two agricultural soils. This method conveniently identified positive iPSB strains and effectively prevented fungal cross-contamination. Maximum-likelihood phylogenetic trees of the isolated strains showed that Bacillus megaterium was the most dominant iPSB, and strains Y99, Y95, Y924 and Y1412 were selected as representatives for the analysis of P solubilization. Succinic acid was the main organic acid of B. megaterium for releasing P. It was strongly correlated with the increase in soluble P concentration during 168 h of incubation of these four strains. pH was negatively exponentially correlated with the amount of soluble P in the medium, and the amount of succinic acid was strongly linearly correlated with the amount of P released (P < 0.001), suggesting that organic acid may mobilize microbial P. Our study provides an efficient and effective method for identifying and analyzing the growth of iPSB strains able to solubilize inorganic P and gives a better understanding of the mechanism of P solubilization.