Use of lactic acid bacteria as a biological agent against the cyanobacterium Anabaena flos-aquae

Abstract

In the present study, we assessed whether lactic acid bacteria (LAB) with antimicrobial activity could be used to effectively control Anabaena flos-aquae growth. In our screening of cyanobacteriacidal bacteria from 14 LAB strains belonging to 11 species, we selected six candidate strains that could lyse 90 % or more A. flos-aquae cells compared with a control. Of those, Lactobacillus paraplantarum KCTC 5045(T) had the strongest cyanobacteriacidal activity showing complete lysis of cyanobacterial cells at the initial densities of a parts per thousand yen10(4) cells mL(-1). A host range assay revealed that L. paraplantarum strongly inhibited A. flos-aquae, Anabaena crassa, Stephanodiscus hantzschii, and Peridinium bipes but weakly inhibited or stimulated the growth of Scenedesmus actus, Pediastrum sp., Cyclotella meneghiniana, Coelastrum reticulatum, Chlamydomonas sp., and Microcystis aeruginosa. In the microcosm experiment using natural freshwater including abundant phytoplankton assemblage, moreover, the LAB under inoculation of about 10(5) cells mL(-1) could completely terminate the co-growth of A. flos-aquae, A. crassa, Anabaena circinalis, and other Anabaena spp. (over 10(4) cells mL(-1)) without a secondary bloom by another algal and cyanobacterial species. Our observation revealed that the cyanobacteriacidal bacterium releases two or more extracellular compounds possessing cyanobacteriacidal activity without cell-to-cell contact when the host cyanobacterium necessarily exits in surrounding water. Property study of cyanobacteriacidal substance revealed the release of heat stable and hydrophobic chemical substances that do not appear to be protein and peptide compound. Taken together, our results indicate that LAB may be a potential bio-agent for future use in controlling freshwater Anabaena blooms without causing the problem of pathogenicity if there is no secondary bloom by a resistant species to this bacterium.