Bacterial Community Structure In The Phycosphere Of Microalgae And Bacteria-microalgae Interaction In The Arctic

Phytoplankton and bacteria played an important role in Arctic marine ecosystem and were of great significance in Arctic microbial loop. We analyzed bacterial diversity in the phycosphere of five Arctic microalgae (Fragilariopsis_cf sp., Micromonas sp., Attheya septentrionalis, Thalassiosira sp. and Chlorella sp.). We also investigated physiological and ecological relationship between dominant picophytoplankton-M/cromons sp. and associated bacteria in the Arctic ocean, and compared Micromonas sp.physiological difference between adding Shewanella sp. and adding natural bacteria in arctic seawater. In order to explore the mechanism based on the Arctic dominant phytoplankton-bacteria interaction, we isolated microalgae with important ecological status from the Arctic habitat, and studied microbial community diversity closely associated with these microalgae,it will understand the microbial loop in the Arctic ocean and the ecological role in the microbial loop.Meanwhile,this study will estimate the flow of energy substances, and provide experimental and theoretical basis for "microbial loop-phytoplankton-the key microbial community" coupling interaction in the polar seas.16S rRNA gene of attached and free bacteria in the phycosphere of five microalgae strains during different growth phases was analyzed by polymerase chain reaction-denaturing gradient gel electrophoresis. Bacterial community in the phycosphere of five microalgae was distinct different. Bacteria in the phycosphere of Micromonas sp., Fragilariopsis_cf sp., Attheya septentrionalis and Thalassiosira sp. mainly belonged to Cyanobacteria, a-Proteobacteria and y-Proteobacteria. CFB were detected only in the phycosphere of Micromonas sp. and Fragilariopsis_cfsp.. For Chlorella sp., bacteria in the phycosphere belonged to Cyanobacteria, CFB, a-Proteobacteria, β-Proteobacteria without γ-Proteobacteria. Bacterial community in the phycosphere of Micromonas sp. were stable during different growth phases,while difference between attached and free bacteria from the other four microalgae was significant. Most free bacteria in the phycosphere of three diatom (Fragilariopsis_cf sp., Attheya septentrionalis, and Thalassiosira sp.) belonged to y-Proteobacteria, while free bacteria related with Chlorella sp. was P-Proteobacteria, whereas attached bacteria associated with four microalgae was comprised mainly of Cyanobacteria. DGGE profiles showed the band number of attached and free bacteria associated with Fragilariopsis_cf sp. during the whole growth phase(lag, exponential and stationary) varied except that dominant bands were stable. However, attached and free bacteria of different growth phase associatied with the other four microalgae strains were rather stable, indicating that specific algae-bacteria association was stable.Axenic culture of Micromonas sp. was obtained successfully after treatment of the antibiotics, included ampicillin, neomycin, gentamycin and kanamycin through serial added in the culture.Adding natural bacteria or Shewanella sp. to Micromonas sp. had no obvious effect on abundance of Micromonas sp. during exponential phase (EM) and stationary phase(SM). Change trend in microalgae abundance was almost identical. Microalgae kept in normal growth. Bacterial abundance fluctuated similar between exponential phase and stationary phase. And fluctuating range of associated bacterial abundance during the whole stationary phase was obviously larger than that during exponential phase. TEP abundance was500-3500/mL and no distinct difference among EM, SM and control group.400～600μM of DOC concentration during exponential phase was lower than500～800μM of DOC content during stationary phase. DOC concentration of adding exgenous bacteria was slightly lower that of no exgenous bacteria, indicating that exgenous bacteria consumed organic carbon released by Micromonas sp.. DFAA was no significant difference between the experimental group and control group during exponential phase, whereas DFAA concentration in adding exgenous bacteria was markedly higher than that in control group. DFAA concentration in adding natural seawater increased from20to90μM on day3and DFAA concentration in adding Shewanella sp. increased sharply from 25to140μM, indicating that the growth of microalgae slowed down, and released more organic matter.Adding exogenous bacteria had no obvious effect on the growth of Micromonas sp.According to bacterial diversity structure in the phycosphere, algae-bacteria interation was stable, also indicating that it was affected by exogenous bacteria.