| In recent years, Phaeocystis globosa Scherffel has occurred frequently in thesouthern coast of China, which has made a great negative impact on the safety ofmarine ecosystem and human health. A huge number of gelatin, sugar and hemolysistoxins generated when Phaeocystis globosa(P. globosa) broke out, large amount ofdissolved oxygen was consumed at the same time which led to the death of fish, theDSMP and DMS P. globosa released is one of the factors affecting formation of acidrain, therefore, how to effective control the breakout of P. globosa is a urgencyproblem. In this paper, research object is P. globosa, we try to screen out aigicicalbacteria from the red tide-frequent-occurrence area of Zhuhai, which can effectivelydissolve the cell of P. globosa, the molecular biology of algicidal bacteria, thealgicidal mode and the microstructure of algal cells in the algae-lysing process arestudied, and also we explore the properties of extracellular algicidal substances andspeculate the lytic mechanism, aim at providing a theoretical basis and practicalfoundation for biological control of P. globosa. The results are as follows:1. Seventeen bacterial strains were isolated from the red tide water by traditionalculture, from which one algicidal bacterium named B1were selected and presentedthe best algicidal effect, the removal rate was95.6%The colony was round,2.2microns in diameter, slightly bulge, neat edge, moist and shiny surface, milky white,opaque, rod-shaped, and were confirmed as Gram-positive bacteria. Under the visualfield of scanning electron microscopy, the colony size was about0.7~0.8μm×2.0~2.2μm and atrichous. The strain were identified by the sequences analysis of16S rDNA.The length of PCR products of B1was1542bp. The sequences obtained in this studywas available in GenBank under accession numbers(strain: JN228893). The DNAsequence similarity searches showed that share more than99%sequence homologywith some strain of Bacillus. Therefore strain B1was appraised as Bacillus sp.through biophysics, biochemical and the analysis of its16S rRNA sequence.2. The algicidal activity of the B1strain was bacterial growth-dependent, since the strongest algicidal activity occurred in middle stationary-phase cultures according tothe strain’s growth curve. These results indicated that the bacterial isolate B1showedalgicidal activity through an indirect attack. B1released algicidal compounds whengrown in2216E medium or in P. globosa cultures enriched with additional nutrients.Production of algicidal compounds was nutrient dependent and the algicidal activityof these compounds was concentration-dependent. The sterile condensed bacteria-freefiltrate could effectively dissolve P. globosa, the lyseing process demonstrated bymicroscopy could be described below: surface layer of P. globosa become brokenâ†'the inclusion of algae cell releasedâ†'P.globosa was lysed.3. The molecular weight of the extracellular algae-lysing components of B1areless than3500, the algicidal substances have strong polarity and heat-tolerant, whichstill had good algae-lysing effect after being treated at121°C, and the removal ratewas92.6%. The algae-lysing ability was stronger while the pH value was kept in9.0,ethanol can separate extracellular algae-lysing components from other componetsefficiently. The algae-lysing components have strong antioxidant, it may benon-bioactive molecules which contain acidic or alkaline groups, and may not beprotein, nuclear acid and polysaccharides. |
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