Growth inhibition and microcystin degradation effects of Acinetobacter guillouiae A2 on Microcystis aeruginosa

Strain A2 with algicidal activity against Microcystis aeruginosa was isolated and identified with the genus Acinetobacter on the basis of phenotypic tests and 16S rRNA gene analysis. It was identified with the species Acinetobactor guillouiae by partial rpoB sequence analysis. When 10% (v/v) of the bacterial culture was co-incubated with M. aeruginosa culture, algicidal efficiency reached 91.6% after 7 days. Supernatant of A2 culture showed similar algicidal activity, while the cell pellet had little activity, suggesting that Acinetobacter guillouiae A2 indirectly attacked M. aeruginosa cells by secreting an extracellular algicidal compound, which was characterized as heat-stable. A significant decrease in the microcystin (microcystin-LR) concentration was observed after 10% (v/v) addition of A2 culture. Transcription of three microcystin-related genes (mcyA, mcyD and mcyH) was also found to be inhibited. The algicidal compound 4-hydroxyphenethylamine was obtained by further isolation and purification using various chromatographic techniques. The EC50, 3d and EC50, 7d values of 4-hydroxyphenethylamine against M. aeruginosa were 22.5 and 10.3 mgL−1, respectively. These results indicate that A. guillouiae strain A2 inhibits growth of M. aeruginosa and degrades microcystin production. The identified compound, 4-hydroxyphenethylamine, has potential for development as a new algicidal formulation or product.