Algicidal Activities Of Marine Bacterium Isolated From A HABs Area, South China

Harmful algal blooms (HABs) in coastal waters have made a great negative impacton marine environment and ecosystem, aquaculture industry and human healthworldwide. There are a number of strategies that can mitigate HABs, including physicaland chemical means, but none of these methods has been totally successful due to thehigh cost and potential dangerous to the aquatic ecosystems. Therefore, it is urgent andbeneficial to develop a more economical and environment-friendly algicidal agents tocontrol HABs. It has been reported that certain marine bacteria play an important role ininhibiting the growth of red tide phytoplankton. Many bacterial strains isolated fromHABs affected waters have algicidal effective on several HABs species. Thus, thealgicidal bacteria could potentially be of great use in HABs controlling. In this paper,11marine algicidal bacterial strains against Scrippsiella trochoidea，Prorocentrum micans，Skeletonema costatum and Phaeodactylum tricornutum were isolated from a HABsarea of Mirs Bay using liquid infection method with48-well microplate, identificationof the bacterium, algicidal mode and algicidal activity were undertaken. The objectiveof this study is to find a safe and feasible biological method to control HABs. Theresults are as following:1. Five marine bacterial strains named N3, N5, N10, N21and N29showingalgicidal activity against S. trochoidea were isolated from Mirs Bay in south China. Inthe test of algicidal bacterium, S. trochoidea cells lost its moveability, then inflated andfinally lysed. The algicidal activity was in a concentration-dependent manner. Thebacterial cultures added at volume fraction of2%(v/v) showed the strongest algicidalactivity, the mortality of algae cells exposed to algicidal bacterium were90%-100%within120h. Followed by1%,95%-100%S. trochoidea lysed within120h except thetest of strains N3and N10, in which alga cells kept increasing. Meanwhile, in the test of0.1%, there were no significant algicidal activities at all. Simultaneously, the density ofstrains N5, N10, N21and N29changed in fluctuation, while strain N3decreasedgenerally. The results showed that S. trochoidea lysed by heat stable algicide(s) releasedby strain N21, while lysed by strains N3, N5, N10and N29directly.2. Bacterial strains N3, N5, N10and N29against P. micans were isolated, in thetest of algicidal bacterium, P. micans cells lost its moveability, then inflated and cellular components aggregated, and finally lysed. The bacterial cultures added at volumefraction of10%(v/v) showed the strongest algicidal activity, the mortality of P. micansexposed to algicidal bacterium were97%-100%within120h, excepted that of strain N3,in which only78%algae cells lysed. Followed by5%, the mortalities of P. micans were95%-100%at120h. While, in the test of1%, there were no significant algicidalactivities at all. Simultaneously, the density of strains N5, N10, N21and N29changedin fluctuation, while strains N5and N10decreased generally. The results showed that P.micans lysed by heat stable algicide(s) released by strain N29, while lysed by strains N3,N5and N10directly.3. Four marine bacterial strains named P1, P5, N5and N21showing algicidalactivities against S. costatum were isolated from Mirs Bay. The algicidal phenomenawere different among the four strains. In the test of P1, N5and N21, S. costatum cellswhich linked chains were broken apart to single cell, in which cellular componentsaggregated, followed by individual cell inflated, and finally lysed, while chains algaewere directly decomposed by strain P5. The bacterial cultures added at volume fractionof10%(v/v) showed the strongest algicidal activity, all S. costatum cells lysed within120h by strains N5, N21and P5, while99%algae cells exposed to strain P1lysed.Followed by5%, all the S. costatum cells lysed by strains N5, P5and N21, and only73.4%S. costatum cells which exposed to strain P1lysed within120h. Meanwhile,which at1%, the number of S. costatum cells were still increasing. The density of strainP1changed in fluctuation after sharply decreased in first24h. Bacterial densities ofN21and P5were in downward trend after increasing at fist, while, the change of strainP5was in fluctuation. S. coatatum lysed by heat labile algicide(s) released by strain P1,while lysed by strains P5, N5and N21directly.4. Bacterial strains P4, P14, N4and N15against was isolated, in the test of thesealgicidal bacterium, the shape of P. tricornutum changed from triangle and prismatic tocolumnar, then aggregation, deposition and dead. The bacterial cultures added at volumefraction of10%(v/v) showed the strongest algicidal activity, all P. tricornutum cellslysed within120h by bacterial strains excepted that of strain P4, which only10%algaecells lysed. Followed by5%, all algae cells exposed to strains N4and N15lysed within120h, while42%and78%P. tricornutum lysed by strains P4and P14, respectively. Inthe test of1%, there were no significant algicidal activities at all. Simultaneously,Bacterial density of P4was in downward trend after increasing at first. While, thedensity of strains P4, N4and N15changed generally in fluctuation. The results showedthat P. tricornutum lysed by heat stable algicide(s) released by strain N4, while lysed bystrains P4, P14and N15directly.5. Sequence analysis based on16S rRNA and performed by BLASTN, combined with morphological and physiological biochemical characteristics of bacteria showedthat strains N3, N4, N15, N29and P1belonged to family of Bacillaceae, in whichstrains N3, N4and N29were genus of Bacillus, N15and P1belonged to Halobacillussp. Strain N5belonged to genus of Kangiella in γ-proteobacteriacea. Strains N10, P5and N21were genus of Muricauda, Muricauda and Roseivirga in Bacteroidetes. StrainsP4and P14belonged to genus of Micrococcus and Aeromicrobium in Actinobacteria,respectively.