Response Of Soil Bacterial Communities To The Sediment Introduced Into The Field In The Xiaokai River Irrigation Area And Multiphase Taxonomic Identification Of A New Bacterium

(1)Response of soil bacterial communities to the sediment introduced into the field in the Xiaokai River irrigation areaAs the second longest river in China,the Yellow River played an important role in the economic and social development of northern and northwestern China.Inevitably,irrigation with the Yellow River water would introduce the Yellow River sediment to the fields.The sediment problem of the Yellow River has always been one of the important factors affecting the sustainable development of the Yellow River Delta.Xiaokai River irrigation area created a precedent for large-descending and long-distance sand transport technology,which was an effective method to solve the problem of sediment in the Yellow River Irrigation Districts.It transports the Yellow River water with high sediment content to the sedimentation tank built in the middle of the canal through the main channel of the sediment transportation.In this way,the upstream uses the muddy irrigation mode where the sediment is directly introduced into the field,and the downstream uses the clear water irrigation method.Soil bacterial communities play a vital role in agricultural production and are important players and defenders in soil biochemical processes.Many factors have an impact on the abundance and diversity of soil microbes,such as irrigation,farming methods,fertilizers,heavy metals,soil types,etc.However,there were few studies on the response of soil microbial communities to sediment introduced into the field.In this study,we investigated the effects of soil sediment introduced into the field on soil bacterial communities through Illumina MiSeq sequencing approach.We analyzed four farmland sites(S1,S2,S3,and S4)irrigated with water containing the Yellow River sediment in the upper reaches of the Xiaokai River irrigation area and four downstream farmland sites that were irrigated with water that did not contain the Yellow River sediment(C1,C2,C3 and C4).Our results revealed that the Yellow River sediment could improve the soil quality,including improving the soil organic matter(SOM)and available potassium(AK)content,and reducing the soil pH and salt content.The soil studied in this study mainly encompassed ten phyla,among which Proteobacteria and Acidobacteria were dominant in both groups.In addition,the main phyla contents in the two groups were significantly different.The predominant genera significantly differed between the two different treatments.Through LEfSe analysis(LDA>2),we screened several biomarkers at the level of the phylum and genus to distinguish the soil containing the Yellow River sediment and the Yellow River sediment-free farmland soil.For example,at the level of the phylum,Proteobacteria and Caldithrix were more abundant in the S group,while Acidobacteria,Nitrospirae and Armatimonadetes were more abundant in the C group.At the genus level,15 genera such as Pseudomonas,Flavobacterium,and Cellvibrio were more abundant in the S group,and 20 genera such as Pontibacter,Nitrospira,and Pirellula were more abundant in the C group.According to the Venn graph analysis,the number of OTUs in the Yellow River sediment group(S group)was more than that in the sediment-free group(C group),and the number of overlapping OTUs in the two groups was 1890.These results indicated that there was a large difference in bacterial communities between the two groups.Heat map analysis showed that the bacterial communities in the S group and the C group were divided into two clusters,showing a clear difference in bacterial community structure between the two groups and indicating that the soil bacterial community in this area was significantly affected by the Yellow River sediment.Through the heatmap of Spearman's correlation analysis,we found that there was a significant correlation between soil bacterial community and soil physical and chemical properties at the level of phylum and genus.These findings provided important insights into the bacterial community structure in this unique irrigated ecosystem in the Xiaokai River irrigation area.It offered some useful information for studying the effects of the sediment introduced into the field on soil bacterial communities.In addition,it also enhanced the understanding of the main factors that changing the bacterial communities.These were very important for the scientific management of soil microbes and sustainable agricultural production in the Yellow River Irrigation District.(2)Multiphase taxonomic identification of a new bacteriumA Gram-stain-negative,rod-shaped bacterium,strain 4-12~T,was isolated from the rhizosphere of Triticum aestivum L.from the Xiaokai River irrigation area,China.The isolate grew optimally at 30?,pH 7.5-8.0,and with 1.0%(w/v)NaCl.The new strain had strong resistance to the ampicillin and was sensitive to the streptomycin sulfate.Based on the 16S rRNA gene sequence and phylogenetic analysis,strain4-12~T belonged to the genus Luteimonas with the highest degree of 16S rRNA gene sequence similarity to Luteimonas tolerans UM1~T(97.68%),followed by Luteimonas terrae THG-MD21~T(97.67%),Lysobacter panaciterrae Gsoil 068~T(97.21%),and Luteimonas aestuarii B9~T(97.16%).However,the DNA–DNA relatedness value between strain 4-12~T and closely related Luteimonas strains was well below 40%.Moreover,according to the measured genome-wide framework analysis,the average nucleotide identity(ANI),the average amino acid identity(AAI),the tetra-nucleotide signatures(Tetra)and the genome-to-genome distance calculator(GGDC)also showed low relatedness between strain 4-12~T and the type strains in genus Luteimonas.Ubiquinone-8(Q-8)was the predominant quinone of the strain 4-12~T.The major fatty acids were iso-C15:0,iso-C11:0,iso-C17:0,and iso-C17:1?9c.Polar lipids were dominatedbydiphosphatidylglycerol,phosphatidylethanolamine,phosphatidylglycerol,and unidentified phospholipids.The DNA G+C content was69.5%.The respiratory quinone,major fatty acid,polar lipids and the DNA G+C content are consistent with the characteristics of the genus Luteimonas.According to the phenotypic,genetic and chemotaxonomic data,strain 4-12~T was very different from its similar type strain,and was considered to represent a novel species in the genus Luteimonas,for which the name Luteimonas rhizosphaerae sp.nov.was proposed.The strain 4-12~T was stored in the China Center for Type Culture Collection(CCTCC)and the Korean Collection of Type Cultures(KCTC),respectively,under the accession numbers CCTCC AB 2016261T and KCTC 52585T.The discovery of this new strain enriched the diversity of the genus Luteimonas and provided microbial and genomic resources for subsequent application studies.