Microbial Community Diversity Of The Surface And Intermediate Seawater And A Columnar Sediment Of Maluku Strait In Tropical Western Pacific

Different water masses are carried by complex currents in Tropical Western Pacific (TWP). One of the important currents is the North Equatorial Current (NEC) which differs into two currents:Kuroshio which moves towards north and Mindanao Current which goes towards south. Mindanao Current is the source of Indonesian Throughflow (ITF) which results in the transport of seawater from the Pacific Ocean to the Indian Ocean. Currents and water masses in this area influence the microbial community structure of the seawater and sediment. In this study, the microbial community structure of the seawater samples which are collected from the two depths (5m and 500m) in the position where currents through and a columnar sediment of Maluku Strait in Tropical Western Pacific are explored. Through high-through sequencing and the analysis of diversity of the V4 variable region on 16S rRNA genes, the microbial community structure of 20 seawater samples which are collected from 10 different positons on the mainstreams in Tropical Western Pacific are obtained. The results show that Proteobacteria is the main advantages of categories in all samples, but Cyanobacteria and Proteobacteria share the maximum abundance in the surface layer (5m) samples because of the influence of the light. The group of Crenarchaeota which is widely distributed becomes the second maximum abundance phylum in the samples at the depth of 500m. Obvious dissimilarity of the community structure is observed in the two sample groups of 5m and 500m. Depth is a principal factor which leads to the differences of microbial community structure in samples. Compared to the sampling depth, the effect made by the currents and water masses is weak and lack of regularity. Generally currents have an effect on a certain position. E121.5.12 which is collected from the depth of 5m is distinctively different from the other samples which may influenced by the special currents in this position. The positon E121.5 is located in the Bass Strait where influenced by the Kuroshio and the circumfluence in the South Sea. As a result, the abundance of Cyanobacteria does not reach a high value like the other surface samples, but the abundance of Verrucomicrobia is much higher. Investigation of microbial community structure in a wide-range area-the Tropical Western Pacific is a significant foundation to know the basic information of microbial distribution and to propel the further study about functional community and the relationship between the microorganisms and environment.The sediment samples are collected from Maluku Strait at a depth of 1250 m in Tropical Western Pacific, which is influenced by Mindanao Current and Indonesian Throughflow. Based on 16S rRNA clone libraries, the community structure and vertical distribution of archaea and bacteria are studied in a 2m length columnar sediment. From the surface sediment, sequences derived are affiliated with fourteen bacterial phyla (Gammaproteobacteria, Planctomycetes, Alphaproteobacteria, Deltproteobacteria were dominant), but are limited to two groups of archaea: Crenarchaeota (99%) and Euryarchaeota (1%). Besides,90% of the archaea clones are ammonia oxidation-related which indicates that the ammonia-oxidizing archaea might make a significant contribution to the chemosynthesis in the surface sediment. Contrastively in the 2m depth sediment, six bacterial phylogenetic groups are obtained (Gammaproteobacteria and Firmicutes were absolute dominant), however no archaea 16S rRNA is detected. The microbial diversity of surface sediment is much higher than the 2m depth sediment and unique bacterial phyla ware obtained from two samples respectively. The geochemical elements analysis reveale that the content of C, TOC and S in the surface sediment is much higher than the 2m depth sediment, but the content of P is contrary. According to the analysis of the microbial structure and the environmental factors, their features coincide. This might be in response to the geochemical substance transfer and deposit influenced by the ocean current.