Diversity And Electrical Activity Of Iron-cycling Bacteria In Coastal Wetlands Of The Yellow River Delta

Iron is one of the most abundant variant valence metal elements.Iron-reducing bacteria(IRB)and iron-oxidizing bacteria(IOB)play pivotal biogeochemical roles in the coupling of iron and carbon or nitrogen redox cycles.In the coastal wetland environments,pattern in abundance,diversity of IRB and IOB can provide evidence of their contribution to biogeochemical cycles in assessing their community structural distinctions associated with spatial variations of nutrients in different habitats.As a typical coastal wetland,the Yellow River Delta is one of the most active regions of wetland-river-sea interaction in the world.In this study,spatial patterns and community structures of IRB and IOB in soil/sediment samples from the Yellow River estuary through intertidal wetland to coastal marine environments were investigated.Deep sequencing of bacterial 16 S rRNA gene and rRNA in field and enrichment samples revealed significant shifts in diversity and distribution of bacterial community,iron-reducing and-oxidizing bacterial communities in sediment samples from the Yellow River estuary to Bohai Sea,and in wetland soils with different salinity gradient.The effects of biogeochemical variables along the gradient on the abundance and biogeographic patterns of bacteria,putative IRB and IOB in sediments were investigated.Aggregates with iron reduction and electrical activity were obtained.AQDS and granular activated carbon can obviously promote extracellular electron transfer for the aggregate.The co-occurrence of Geobacteraceae and Methanosarcina mazei and their activities in an iron(III)-reducing microbial community from a coastal gold mining river has been found.The main results were summarized as follows:Differences in bacterial community composition indicate that community diversity and spatial distribution of bacteria in sediments from the typical coastal area with land-river-sea interaction are mainly determined by biogeochemistry and habitats.Yellow River sediment had the highest diversity and was dominated by hydrogen-,nitrogen-and iron-cycling bacteria,such as Hydrogenophaga,Nitrospira,Pseudomonas,and Thiobacillus.The intertidal wetland had a haloduric community with diverse function(such as Planctomyces,marinobacter,Halomonas,Salinivibrio and Salinibacter).The Bohai Sea sediment had higher relative abundances of Lutimonas,Desulfococcus,Photobacterium,Propionigenium,and Vibrio.Salinity,p H and SO42-concentration were key parameters,which contributed to variations in the bacterial communities.Relative abundance of IRB and IOB in samples from intertidal wetland with different salinity gradients showed distinct responses to salinity,revealing considerable spatial heterogeneity even within this relatively small site..The diversity of iron-reducing bacterial populations was negatively correlated with soil salinity,while the diversity of iron-oxidizing bacterial populations was positively correlated with soil salinity.Iron-reducing bacteria Geobacter,Pseudomonas,Thiobacillus,Bacillus and Anaeromyxobacter,together with iron-oxidizing bacteria Gallionella and Thermomonas species were predominanted in soil samples with low salinity(Blendimings and Phragmites),respectively,whereas Bacillus,Desulfovibrio,Clostridum and Marinobacter species were the dominant iron-reducing and-oxidizing bacteria in soil samples with high salinity(Suaeda and Tamarix),respectively.Soil samples with low salinity have higher activity of iron(III)reduction.Change in relative abundance and spatial distribution of iron-reducing and-oxidizing bacterial communities in sediment samples from the Yellow River estuary to Bohai Sea,revealed substantial spatial heterogeneity between two ecosystems.Community diversity and spatial distribution of the IRB and IOB in sediments from the typical coastal area with river-sea interaction are mainly determined by biogeochemical factors and habitat type.Relative abundance and diversity of IRB and IOB in sediments from the Yellow River estuary were higher than those from the Bohai Sea.We found that Pseudomonas,Thiobacillus,Geobacter,Rhodoferax,Clostridium and Azospira,Gallionella,Rhodobacter,Thermomonas were the most abundance genera of IRB and IOB in sediments from the Yellow River estuary.And the dominant genera in sediments from the Bohai Sea were Vibrio,Shewanella,Thiobacillus and Marinobacter.The opposite trend was observed in enrichment cultures compared to in situ samples,indicating that relative abundance of IRB in marine sediments can be promoted in the presence of amorphous iron oxides in enrichment culture.However,sediment samples from river have higher activity of Fe(III)reduction than those from marine.Shifts in diversity of putative iron-reducing,iron-oxidizing and nitrogen-cycling bacteria discovered a novel distribution pattern in Yellow River estuary and adjacent Bohai Sea.There are the higher relative abundances and diversities of putative iron-reducing,iron-oxidizing and nitrogen-cycling bacteria at coastal transitional sites.Relative abundance of well-known nitrogen-cycling bacteria was positively correlated with relative abundance of iron-cycling bacteria.Additionally,concentrations of TN,NH4+-N and NO3--N contributed to variations of iron-reducing and-oxidizing bacterial communities.Aggregate C1 with iron reduction activities formed by Desulfovibrio and Pseudomonas was isolated from coastal wetland.Differences in relative abundances of Desulfovibrio and Pseudomonas in aggregate C1 were observed when offered with different types of organic substrates.The effect of salinity on Fe(III)reduction of aggregate C1 was little in cultures with ethanol as the only electron donor.AQDS and granular activated carbon can obviously promote electron transfer between aggregate C1 and Fe(III)oxide.Aggregate produced higher electrical density in microbial fuel cell with dialysis bag,revealing it may use electron shuttle for extracellular electron transfer.The co-occurrence of Geobacteraceae and Methanosarcina mazei and their activities in an iron(III)-reducing microbial community from a coastal gold mining river,Jiehe River,has been found and confirmed by culture independent molecular techniques based on 16 S rRNA and rRNA,respectively.Aggregates,as close physical contact necessary for direct interspecies electron transfer(DIET),have been found in the culture with ethanol as electron donor after three transfers,and indicated the possibility of DIET between them.The enrichment cultures actively contained the bacteria belong to Geobacteraceae and Bacilli,exclusively dominated by the archaea belong to Methanosarcinaceae.