The Community Structure Piezophiles And The Environmental Adaptation Mechanism Of Novel Piezotolerant Novel Strain From Deep-sea Sediment

The deep sea is the largest ecosystem on Earch,which can be divided into bathyal zone(1000-3000m),abyssal zone(3000-6000m)and hadal zone(6000-10000m)according to the depth.The deep sea is considered a “window” into the Earth's primitive environment,with multiple extreme conditions of high pressure,low temperature,darkness and oligotrophic.Among these,pressure is the most significant environmental factor in the deep-sea.However,how pressure affects deep-sea microbial community structure remains unclear.Therefore,it is of great significance to study the origin and evolution of life,by exploring the relationship between deep-sea microbial community structure and extreme environmental factors(e.g.,high pressure),and analyzing their adaptation mechanisms.In this paper,based on the samples of hadal and abyssal sediments from the Yap Trench of the Pacific Ocean collected by the world's most advanced manned submersible "Jiaolong",we studied the characteristics of the piezophiles/piezotolerant community structure and their relationships with environmental factors by using different culture conditions,and explored their adaptation mechanisms to deep-sea extreme environment.Sediment samples from five different stations in the Yap Trench were incubated at different pressures(60MPa and 0.1MPa),nutrients(high and low)and subculture(first and second).The community structure of under different enrichment conditions was analyzed and compared with the community structure in situ.We found that the microbial community under high hydrostatic pressure(HHP)and low nutrition conditions of enrichment was closest to those uncultured in situ.Therefore,the HHP and low nutrient conditions were considered to be the most suitable for the growth of microorganism in the Yap Trench.Meanwhile,pressure is the biggest factor affecting the microbial community structure,followed by nutrition.The piezotolerant and piezophilic microbial community in Yap Trench mainly include Nitrososphaeria class of Thaumarchaeota,?-,?-and ?-Proteobacteria,as well as S085 of the Chloroflexi and Phycisphaerae class of Planctomycetes.Thaumarchaeota is the dominant group in Yap Trench sediments,and 90% of them belong to Nitrososphaeria,Nitrosopumilaceae.Thaumarchaeota is a typical ammonia-oxidizing archaea and can fix carbon dioxide,so it could play an important role in the C and N cycles of the Yap Trench ecosystem.There are distinct differences in the distribution of microbial trophic types in the abyssal and hadal zones of the Yap Trench.From abyssal zone to hadal zone,chemoautotrophic bacteria gradually decreases,while heterotrophic bacteria gradually increases.More heterotrophic ?-Proteobacteria and Bacilli were found in hadal zone than in the abyssal zone.There are also considerable differernces in the community structeure of enriched microbial under HHP and low nutrient culture conditions between two zones in Yap Trench.For example,?-Proteobacteria increases significantly in the abyssal zone,but Nitrososphaeria and SAR202 clade increases significantly in the hadal zone.Therefore,HHP and low nutrient culture conditions play an important role in obtaining piezotolerant and piezophilic microorganisms from abyssal and hadal zonesIn order to obtain more deep-sea microorganisms,sediment samples from the hydrothermal zone and Yap trench were enriched and cultured under different temperature and pressure conditions together,and then isolated and purified under atmospheric pressure conditions.More than 1000 strains of piezotolerant bacteria were obtained.Fortunately,8 novel piezotolerant strains were obtained,including Oceanobacillus piezotolerans YLB-02 T,Lysinibacillus yapensis YLB-03 T,Bacillus piezotolerans YLB-04 T,Marinomonas piezotolerans YLB-05 T,Shewanella psychropiezotolerans YLB-06 T and YLB-07 T,Shewanella eurypsychrophilus YLB-08 T and YLB-09 T,which can grow in 0.1-50 MPa.These novel piezotolerant strains not only enrich the resources of piezotolerant microorganisms,but also provide a scientific basis for further exploration of the pressure adaptation mechanism of deep-sea microorganisms.Shewanella psychropiezotolerans YLB-06 T was chosen as the representative to study the pressure and cold adaptation mechanism.The genome of YLB-06 T had many multiple copy genes,including double flagella system,multiple chemotaxis systems,six pili systems,multiple antioxidant genes,multiple gene clusters of tolerating heavy metals,10 pairs of toxin-antitoxin systems and 3 sporulation-related proteins.These characteristics were related to its adaptation to the high pressure and low temperature environment in the deep sea.Meanwhile the whole genome of YLB-06 Twas the largest known genome of Shewanella.Through evolutionary analysis of Shewanella genus from upper ocean to deep sea and then to abyssal and hadal zone,YLB-06 T was found to play a connecting role between deep sea and abyssal zone.Transcriptome analysis found that the significantly up-regulated differentially expressed genes under high pressure and low temperature conditions were mainly related to metabolism,including amino acid metabolism,carbon metabolism,and energy metabolism.Hence,Shewanella psychropiezotolerans YLB-06 T could adapt to the deep ocean enviroment by using multiple modalities in movement,attachment,biofilm formation,cell-to-cell interactions,then accumulating amino acids,flexibly choosing carbon metabolisms and energy metabolisms to obtain more energy.In conclusion,Thaumarchaeota is the most dominant group in the investigated sediments of Yap trench.HHP and low-nutrient conditions are suitable for the enrichment and culture deep-sea microorganisms.8 novel piezotolerant species were obtained through enrichment by HHP.Shewanella psychropiezotolerans YLB-06 T has multiple strategies to adjust to the deep sea extreme environment.Therefore,this study provides a reference for understanding the deep sea microbial community structure and their adaptation mechanism to the deep sea extreme environment.