Cold-adapted Ecotype Differentiation Of Marine Polaribacter

Marine heterotrophic bacterioplankton are the major consumers of marine organic matter.One of the most abundant bacterioplankton Bacteroidetes phylum are wildly distributed in different marine ecosystem.Flavobacteria,belongs to Bacteroidetes,owes more than 140 genera and has great diversity.High abundance has been linked to cold waters,upwelling systems,coastal and phytoplankton blooms.Considering its high abundance and ability of degradation of high molecule matters,Flavobacteria is regarded as degraders of biopolymers released by phytoplankton and plays a key role in global carbon cycle.Previous studies had showed that Polaribacter is the dominant genus of Flavobacteria especially in cold waters and phytoplankton blooms.Based on 16S rRNA genes similarity and in situ hybridization,it has been suggested that Polaribacter genus consists of cold-and warm-water phylotypes and the cold-adapted one is dominant in high latitude water mass of less than 10�C.It is known that 71%Earth is covered with ocean and over 90%seawater temperature is lower than 5�C which means most ecosystem is under low temperature.Therefore,exploring the cold-adaptive strategies of Polaribacter helps us to understand the diversity and distribution patterns of marine microbes.However,there are only 27 Polaribacter whole genomes and the cold-adaptive strategies they perform in order to become dominant is little known.Here,we collected 11 single cells belongs to Polaribacter from Gulf of Maine and Antarctic surface seawater.Bioinformatics analysis was performed by using all the accessible sequences of Flavobacteria and Polaribacter from public database,including metagenomic sequences,16S rRNA amplicon and Polaribacter whole genomes.Besides,we used comparative transcriptomics to characterize and compare three typical Polaribacter strains,the major results are showed below.(1)By using public metagenomic database data and 16S rRNA clone library(NCBI,EMBL,iMicrobe),we describe the distribution characteristic of Flavobacteria and Polaribacter in global surface ocean.Flavobacteria has a wide distribution in global surface ocean especially the polar and costal in which the relative abundance was up to 64%bacterioplankton.Likewise,Polaribacter was the dominant Flavobacteria in cold water indicating a preference for colder water.(2)Using single cell genomics,we obtained 11 Polaribacter single cell genomes from surface seawater of Gulf of Maine and Antarctic ocean which greatly extend available Polaribacter genomes.Thus,a relative complete Polaribacter genome tree was constructed which suggested group I is a cold water phylotype in Polaribacter.By comparing the distribution of group I and others,we verify the hypothesize that the ecotype differentiation of Polaribacter in which group I is a cold-water ecotype.(3)To characterize and compare the cold-adaptive strategies of three typical Polaribacter strains,transcriptomic analyses under short-term(72 hours at 0?)and long-term(30 days at 0�C)cold stress were performed.The results showed that Polariba.cter irgensii 23-P maintained a similar transcriptional level at long-term low temperature comparing with higher temperature which indicated its powerful cold-adapted ability.P.filamentus maybe still at the early stage of cold adaptation process after long-term acclimation at 0�C while most metabolisms of P.sejongensis were significantly suppressed at long-term cold stress.Accordingly,we illustrate that the better cold-adaptive strategy makes the cold-ecotype group I the dominant Polaribacter in cold water.