Resumo

Introduction Until now, microalgae is provided as one of the initial diet in aquaculture. Moreover, studies focused on their biocontrol activity are increasing recently. However, published papers mainly concentrated on the log phase of microalgae as it was usually used as feed or in some experienments like microbiota analysis. Therefore, the aim of the present study is to reveal the several microalgal microbiota under different growth stage and evaluate the possible antagonistic activity of their Extracellular organic compound (EOC) against pathogenic bacteria as a biocontrol agent. Furthermore, we also evaluate the influence of EOC in enhancing the antibacterial activity of probiotic strain against pathogenic bacteria. Materials and methods Firstly, three microalgae (Phaeodactylum tricornatus; Pt, Tetraselmis suecica; Tet, Nannochloropsis gaditana; Nano) were used to compare the microalgae-associated microbiota in the different growth stage (early and late; log and stationary phase) using Denaturation gel gradient electrophoresis (DGGE). Then, two probiotic strains (SLP1 and C32), which showed antagonistic activity against pathogenic bacteria, were isolated. After that, we evaluated the antagonistic activity of EOC with/without probiotic strains using co-culture assay. Result Result from DGGE band pattern, microbiota composition of Tet showed the different composition only in the late stationary phase, whereas that of Pt and Nano was similar in all different stages. Moreover, microbiota composition of Pt was totally different from that of culture water. In the case of Nano, microbiota composition of culture water was adapted from Nano associated microbiota. Result from co-culture assay showed antagonistic activity only in Nano with/without probiotics of the late log phase and no growth in the early log phase. Thus EOC of Nano alone is responsible to inhibit pathogenic bacteria. Conclusion Our study revealed the differentiation of microbiota composition associated with each microalgae in the different growth stage. Although Nano associated microbiota composition is stable, it suggested that EOC of Nano at the different stage showed different degree of antagonistic activity. This work was financed by Fondef D10I1050.