Archaeal Communities And Response To Bioremediation In Intertidal Mudflats Of Fujian Coast

Intertidal mudflat is closely related to human life.With the increasing interference caused by human activities,it has experienced pollution in different degrees.Bioremediation has attracted more and more attention because it is more effective,economical and environment friendly than physical or chemical treatment.Macrobenthos,such as shellfish and polychaete,have been used in bioremediation of aquaculture ponds.As important participants in the coastal ecosystem biogeochemical cycle,micro-organisms exert great influences on nutrients transportation,organic matter degradation and pollutants transformation.Micro-organisms respond rapidly to environmental changes,and thus can be served as an important indexes for environment monitoring.Archaea is one of the main group of marine microbes,it could not only survive in extreme conditions,but also in normal marine environments.With its huge abundance,archaea is playing a very important role in the biogeochemistry processes on the Earth.Despite that a few studies had reported the archaeal diversity in many environments,the studies regarding archaea in mudflat sediments were not enough,and the archaeal community response to bioremediation has not been reported bef-ore.In this study,macrobenthos(Perinereis aihuhilensis,P.nunia and 7egillarca granosa)were artificially introduced to mudflat sediments for repairing the environment in Sansha bay and in laboratory simulation experiment in Jimei.The traditional physicochemical indexes were investigated and assessed,and the archaeal communities and response to the bioremediation in intertidal mudflats were studied by clone library construction,Restriction Fragment Length Polymorphism(RFLP),DGGE(Denaturing Gradient Gel Electrophoresis)and Illumina Miseq sequencing.The results would provide important bases for understanding archaeal function in bioremediation,assessing bioremediation effects,optimizing bioremediation measures,improving environment evaluation index and,finally for developing real-time and dynamic monitoring system of microbes.The results were as follows:1.The physicochemical characteristics and heavy metal contents of mudflat sediments were investigated and evaluated in a typical enclosed bay(Sansha Bay)and a city type bay(Jimei,Xiamen):All the contents of N,P,and S in Sansha Bay exceed the standard values and the contents of P and S highly exceeded their reference values.The degree of heavy mental potential ecological risk was in the following order:Pb>Cd>Cu>Zn>Cr,the corresponding risk grades were very high,very high,high,moderate and moderate,respectively.The contents of P and S in Jimei are lower than those in Sansha Bay,but they were also well above their reference values.The degree of heavy mental potential ecological risk was in the order of Cd>Pb>Cu>Cr>Zn,the corresponding risk grades were very high,high,high,moderate and moderate,respectively.No matter in Sansha bay or in Jimei,the physicochemical characteristics and heavy metal values did not changed significantly after introducing macrobenthos.2.The archaeal 16S rRNA gene clone libraries of mudflat sediments were constructed in Sansha Bay and Jimei:A total of 283 clones were randomly selected and were divided into 42 RFLP patterns.All the cloned sequences fell into three phyla:the Thaumarchaeota(group MGI),Crenarchaeota(group MCG)and Euryarchaeota(groups MBG-D,MBG-E,VAL III and DHVE 6),in which Thaumarchaeota MGI was dominant,occupying 75.6%of total clones.Crenarchaeota MCG and Euryarchaeota accounted for 15.2%and 9.2%respectively.The archaeal diversity in Xiamen intertidal sediment was lower than that of Sansha Bay.The archaeal diversity in ark shell-introduced sample was higher than those in controls.Introducing ark shell seemed to stimulate the growth of MCG and inhibit the growth of MGI.The archaeal diversity in summer was higher than that in winter in Sansha Bay.3.The active archaeal amoA gene clone libraries were constructed in mudflat sediments of Sansha Bay:A total of 430 effective sequences are divided into 59 OTUs.These OTUs were divided into Cluster M,which derived from sea water and marine sediments,and Cluster S,which derived from soil and freshwater sediment.The Cluster S contained only 2 clones,which indicated that the active ammonia-oxidizing archaea in Sansha Bay were mainly distributed in marine sediments.Introduction of macrobenthos tended to increase the diversity of activity ammonia-oxidizing archaea in most of the samples,and stimulated the growth of those with low content or low activity in their native environment,such as Cluster 4,Cluster 5 and Cluster 10.4.The archaeal communities and response to nereid bioremediation in mudflat sediments of Jimei were investigated by 16S rRNA gene-Illumina Miseq sequencing in laboratory bioremediation model:A total of 574,383 sequences have been detected,95%of them belonged to Thaumarchaeota and Euryarchaeota,and only few sequences were unclassified archaea.At genus level,MGI_unclassified and DHVEG-6_norank were dominant,accounted for 32.87%and 19.19%of total sequences respectively.In this case,clustering analysis of archaea community structure at different taxonomic levels showed that there was no significant difference between macrobenthos-introduced group and control group,or between different sowing densities of macrobenthos groups.Compared with the control group,the abundance of a few genera increased in macrobenthos-introduced groups,many of them were methanogens.On the other hand,the abundance of a small number of gerera decreased after introducing the nereid to the sediments.5.No matter in insitu bioremediation of Sansha bay,or in laboratory bioremediation of Jimei,there were no significant changes in physicochemical characteristics or heavy metal values,whereas the communities of archaea or activity ammonia-oxidizing archaea changed obviously,which showed that archaea responded more rapidly and could be served as an important potential index for environmental monitoring.