Screening and biodiversity analysis of cultivable inorganic phosphate–solubilizing bacteria in the rhizosphere of Hydrilla verticillata

research, the single colony is isolated by picking on NBRIP solid medium for delineation and repeatedly delineated for more than four times, and the colony is inoculated in phosphorus- deficient medium for subsequent phosphate-solubilizing characteristic detection experiments after confirmation as pure cultures. The phosphate-solubilizing characteristic of the screened IPB is stable after repeated transgenerational screening. In this research, we conduct cultivable experiments of IPB in the rhizosphere of Hydrilla verticillata, which enriches microbial resources and also determines the phosphate-solubilizing ability of pure cultures, but do not fully understand the full information of IPB species and potential phosphate-solubilizing functions in the roots and rhizosphere sediments of Hydrilla verticillata. In the future, experiments on phosphate-solubilizing functional genes, such as GDH, GADH and PQQ [29–31], can be carried out by high-throughput sequencing, which can reflect the distribution of phosphate-solubilizing microorganisms in the environment more comprehensively. Meanwhile, in this research, IPB strains are isolated in the laboratory using NBRIP medium and their phosphate-solubilizing ability is determined using ammo- nium molybdate spectrophotometry, but no experiments are designed to verify their phos- phate-solubilizing ability on sediment and their probiotic effect on the growth of Hydrilla verticillata. In the future, it is suggested to select IPB strains with better phosphate-solubilizing

effect, and use microcosm experiments to determine their positive effect on the growth of Hydrilla verticillata. The experiments can be set up as untreated and treated Hydrilla verticil- lata with IPB, and after a period of incubation, the phosphorus content in different parts of Hydrilla verticillata and rhizosphere sediments can be measured to verify whether the IPB could promote the growth of Hydrilla verticillata and the release of phosphorus from rhizo- sphere sediments. The mechanism of the effect of IPB on plant growth also needs to be further investigated. In addition, IPB with the highest phosphate-solubilizing ability in this research can be studied in more detail in the future in order to apply it to the restoration of submerged plants in high-organic matter water. Conclusions A total of 28 cultivable IPB strains are isolated from the rhizosphere of Hydrilla verticillata collected from the high–organic matter urban landscape water. These strains are found to belong to two phyla (Proteobacteria and Firmicutes) and nine genera (Bacillus, Asticcacaulis, Acinetobacter, Aeromonas, Serratia, Exiguobacterium, Comamonas, Ciceribacter and Priestia). Strains SWIH-7, SWIP-6, SWIP-7, SWIP-13, SWIP-15 and SWIP-16 are the poten- tial new species. The results show that the cultivable IPB strains in the rhizosphere of Hydrilla verticillata have a rich diversity, expanding the source of phosphate-solubilizing microorganisms. All the 28 IPB strains could dissolve inorganic phosphorus and have stable phosphate-solu-

bilizing characteristic, but the IPB strains show significantly different phosphate-solubilizing ability. The strain SWIH-9 has the highest phosphate-solubilizing efficiency of 71% and DIP of 55.74 mg/L, while the other strains have phosphate-solubilizing efficiency of 3% to 62% and DIP of 2.19 to 49.26 mg/L. The phosphate-solubilizing ability of the strain is negatively corre- lated with the pH of the solution. It is preliminarily determined that the strains dissolve insolu- ble inorganic phosphorus mainly through acid production, and the specific mechanism needs further research. The IPB strains isolated and screened in this research are rich in diversity, with stable phos- phate-solubilizing characteristic and potential new species. These IPB strains are of great sig- nificance in the future treatment of high-organic matter polluted water and the ecological restoration of water. PLOS ONE Screening and biodiversity analysis of cultivable inorganic phosphate–solubilizing bacteria PLOS ONE | https://doi.org/10.1371/journal.pone.0297047 January 19, 2024 9 / 11