Linking Metabolomics And Proteomics To Reveal The Impact Of Bacteria On Low Molecular DOM Cycling In The Phytoplankton Bloom

Marine phytoplankton perform approximately half of global carbon fixation,with their blooms contributing disproportionately to carbon sequestration,and most phytoplankton production is ultimately consumed by heterotrophic prokaryotes.Therefore,phytoplankton and heterotrophic community dynamics are important in modelling carbon cycling and the impacts of global change.Nutrients pollution and eutrophication have become the main threats to the ecological environment in coastal waters,which have led to algal blooms outbreak frequently in many gulfs and estuaries.By using the high-throughput sequencing technology combined second-generation Illumina with three-generation Pacbio,we investigated the communities and diversities of free-living and partical-associated microbes from Akashiwo sanguinea algal bloom,which occurred in coastal water around Xiamen Island.Combining with the proteome and high-throughput metabolic(FT-ICR-MS,UHPLC-QTOF-MS and UHPLC-QQQ-MS)that applied onto the dominant bacterium,such as Roseobacter,Flavobacterium,Oceanospirillales,we identified the microprocesses of utilization and transformation of dissolved organic matter(DOM)in algal bloom.The main conclusions of this study are as follows.(1)The bacterium in algae bloom are dominated by Roseobacter,such as Lentibacter and Planktomarina,Flavobacterium,such as Polaribacter and NS3a marine group,and the Oceanospirillum(Litoricola).To enhance the competitive advantage during the bloom,all these bacterium are featured by different survival strategies,including partical-associated and free-living type.(2)The three different predominant bacterium are characterized by different metabolisms to utilizing DOM,resulting in an indirectly carbon and nitrogen sources competition,and subsquently maintaining the relationships between different bacterium and phytoplankton.Among the three bacterium,the Roseobacter prefers to utilize the protein and polar lipids which contains high dissolved organic nitrogen(DON)during the bloom.We found that the Roseobacter expressed abundant protein in connection with the metabolism of amino acids and produced ammonium(NH4+)during the metabolic processes.While for the Oceanospirillum,the DOM that contains more CHO was favored to the Oceanospirillum,such as neutral fats and nucleic acids.This kind of bacteria expressed more protein related to transporter,membrane protein and two-component systems.At the same time,the Oceanospirillum produced organic matter that contains CHON via utilizing NH4+.The Roseobacter was more diversification for the metabolism of DOM relative to the Flavobacterium and Oceanospirillum.Our results indicated that N-contained DOM was the main carbon source and the expressive protein was associated with the transporter.However,organic sulfur,such as DMSP,was another carbon and sulfur source for the Roseobacter,and dring the metabolism,NH4+was also produced.(3)Analogous organic matter was produced via the bacterium transforming,even though specific substrates were utilized for the three dominant bacterium.We thus inferred that the generated low molecular DOM(LMDOM)was recalcitrant,and caused a similar DOM features in deep oceans.In conclusion,we suggested that the transformation of the LMDOM,particularly the DON,is the main driver to control and maintain the stable relationship of bacterium and phytoplankton in bloom.The coupling of carbon,nitrogen and sulfur biogeochemical cycles during the utilizing and transforming of DOM,playing significant roles in regulating the oceanic carbon isolation and climate change regionally.