Research Of Relationships Between Marine Microalgae And Bacteria: Several Examples Of Positive And Negative Effects

Environmental improvement and optimization of cultural mode are very important to the healthy and stable development of aquaculture. In this thesis, research of relationships between marine microalgae and bacteria was carried out for the application of that to mariculture. Axenic cultures of 6 species of planktonic microalgae, Skeletonema costatum, Prorocentrum minimum, Scrippsiella trochoidea, Phaeocystis pouchetii, Amphidinium sp. and Platymonas sp. strain 1040 were obtained successfully after treatment of the antibiotics, including penicillin, gentamycin and kanamycin, through serial or mixed added in the cultures. After 4 strains of benthic microalgae, of which 3 were identified as Navicula spp., isolated through plate streaking, axenic cultures of them were obtained for the first time in China after treatment of penicillin, gentamycin, amikacin and erythromycin on the algae grew on the surface of plate (made of L1 medium), the difficulty of benthic microalgal axenation caused by biofilm was resolved. After freed of bacteria, aging phenomenon of Platymonas sp. strain 1040 was almost invisible, it is suggested that some algal-concomitant bacteria could stimulate ageing of the algae 1040. Adhesive ability of one strain of benthic microalgae (Navicula sp.), isolated from Changdao, Shandong province, lost just after treatment of antibiotics, but it could resume when effects of the antibiotics eliminate from the culture completely. Analysis of compositional characteristics of heterotrophic bacterial communities associated with 4 species of planktonic microalgae, Isochrysis galbana strain 3011, Phaeodactylum tricornutum strain 2038, Platymonas sp. strain 1040 andChlorella sp. strain 1061 was carried out. Results showed that bacteria belonged to Pseudomonas, Flavobacterium and Alcaligenes were familiar in heterotrophic bacterial communities associated with the microalgae. After processed by 4 strains of benthic microalgae, constitutes of heterotrophic bacteria in 3 samples of seawater filtered with 0.8μm filter membrane changed, bacteria of Vibrio and Photobacterium could not be dominant, vibrios were ≤5cfu/cm2 according to TCBS plate culture results. After algal autonomous selection, new bacterial communities formed. Just same as compositional characteristics of the natural heterotrophic bacterial communities of 4 speices of planktonic microalgae, Pseudomonas, Flavobacterium and Alcaligenes were familiar in the stable heterotrophic bacterial communities associated with the 4 strains of benthic microalgae. Results showed for the first time that the bacteria, which had not the ability to utilize glucose under anaerobic condition, were familiar with marine microalgae. Three strains of bacteria 3011-11, bNJ-3 and bHN-2, which were isolated from the bacterial communities associated with Isochrysis galbana strain 3011 and benthic microalgae NJ-1 and HN-5, could stimulate growth of Isochrysis galbana 3011 when the bacteria cultured individually with the axenic algae (viatamins omitted). Results indicated that strain3011-11 and strain bHN-2 could produce vitamin B12 or analogues, bNJ-3 could produce vitamin B1 and B12 or their analogues. Growth characteristics of 3 strains of Vibrio , which cultured together with axenic and nonaxenic cultures of microalgae (including planktonic and benthic), and with bacteria isolated from algal-concomitant bacterial communities were studied. Results showed that the nonaxenic microalgae could expel the vibrios ubiquitously; axenic cultures of the microalgae, bacterial iaolates, bacterial communities separated from the algae and the metabolites of the nonaxenic microalgae could not restrict growth of the vibrios. Mixtures of algae and respective single bacterial strain could not expel the vibrios, but mixtures of algae and all respective bacterial strains could resume the ability to restrict growth of the vibrios, the earlier that the stable bacterial communities associated with the algae formed, the earlier that the vibrio-expelling ability resumed. The anti-vibrio mechanism of microa...