Pseudomonas aeruginosa UCBPP-PA14 a useful bacterium capable of lysing Microcystis aeruginosa cells and degrading microcystins

To identify a useful bacterium capable of controlling both Microcystis aeruginosa and microcystins (MCs), 30 strains of Pseudomonas were screened. Two of them (Pseudomonas aeruginosa UCBPP-PA14 and Pseudomonas putida KCCM 10464) could cause significant lysis of M. aeruginosa. PA14 exhibited higher degradation activity against microcystins than KCCM 10464, and hence, it was selected as the bacterium for further analysis. Following its introduction into M. aeruginosa culture (105 cells mL-1) at densities of 107, 105, and 103 PA14 cells mL-1, higher initial inoculations of PA14 removed correspondingly more M. aeruginosa cells (100%, 100%, and 92% at 15, 30, and 10 days, respectively) and degraded microcystin (extracellular MCs: 83.7%, 77.7%, and 51.6% at 30 days; total MCs: 91.0%, 86.9%, and 61.6% at 30 days, respectively). However, the activity of PA14 diminished when its density decreased to less than 106 cells mL-1. At three initial algal densities (106, 105, and 103 cells mL-1), PA14 at a density of 105 cells mL-1 easily and quickly removed algal cells (100%, 100%, and 97.3% at 8, 16, and 30 days, respectively). Host range assays showed that at lower initial PA14 inoculation (105 cells mL-1), the algicidal activity of PA14 was effective species-specifically on M. aeruginosa, while at higher initial inoculation (107 cells mL-1), a wider algicidal range regardless of the general taxonomical relationships was observed. These results indicate that inoculation with 105 Pseudomonas aeruginosa PA14 cells mL-1 into developing natural algal blooms can remove both M. aeruginosa and MCs without causing problems for other algae species.