| Paenibacillus mucilaginosus, a critical silicate bacterium in the biogeochemicalcycling of potassium, phosphorus, and other soil elements, is able to degradeinsoluble soil mineral s with the release of nutritional ions and fixes nitrogen. Thesefunctions make P. mucilaginosus widely used in agriculture as a biofertilizer, inbioleaching as a biocomplexing agent, and in wastewater treatment as a bioflocculant.However, these mechanisms keep unknown. Clarification of adaption to theseenvironments will help to widen its application. Here, comparative genomics andtranscriptome under nitrogen starvation were carried out.Firstly, the comparative genomics were analyzed between P. mucilaginosus andother four paenibacillus strains, including Paenibacillus sp. Y412MC10,Paenibacillus sp. JDR-2, Paenibacillus polymyxa E681and Paenibacillus polymyxaSC2. According to the results, the genome own genes related extracellularpolysaccharide formation, spore formation, and nitrogen metabolism, which werehelpful to adaption to stresses.The genes related to extracellular polysaccharide are similar in P. mucilaginosusKNP414to those in other four Paenibacillus strains. The genome has genes encodingenzyme synthesizing monosaccharide, which might be utilized for polysaccharide.The monosaccharides are mannose, galactose, rhamnose, fructose and so on. Thereare also some genes responsible for activating these monosaccharides, such asUDP-N-acetyl-3-(1-carboxyvinyl)-D-glucosamine, ADP-glucose, UDP-D-glucose,UDP-N-acetyl-D-mannosamine, GDP-alpha-D-mannose, GDP-beta-L-galactose, andUDP-D-glucuronate. These molecules are direct precursor of polysaccharide. Inaddition, the genome has genes encoding glycosyl transferase, which plays animportant role in the synthesis of extracellular polysaccharide. These genes aredivided into three clusters. In the genome, the genes involved in transportation andhydrolysis of xylan were also found in the genome, which might be the source ofxylose for polysaccharide, since the genes encoding xylose is absent in the genome. The genome has a set of genes responsible for spore formation. The genesinclude five regulator genes and many structure-forming genes. The five regulatorsare Spo0A, E, F, K, and G.As the nitrogen metabolism be concerned, nothing genes are found related tonitrogen fixation. However, P. mucilaginosus KNP414has two ways to assimilateammonia. One way is related to glutamine synthase, the other way related toglutamate dehydrogenase. In addition, the genome of KNP414has two uniquepathways of amino acid metabolism: histidine degradation pathway and aspartic acidsynthesis pathway.Secondly, the transcriptome under nitrogen starvation was analyzed. Before this,the phenotypic characteristics were investigated. Capsule and spore were formed at11h post inoculation in nitrogen-free medium. At this time-point, the expressions ofgenes related to extracellular polysaccharide synthesis, spore formation and nitrogenmetabolism were analyzed. And the data of the transcriptome are confirmed usingfluorescence quantity PCR.The expression of genes related to polysaccharide synthesis: in the nitrogen-freemedium, the expression of fructose6-phosphate up-expressed significantly, whichcan transfer many monosaccharide into the corresponding nucleotide sugar. At thesame time, genes related to synthesis of nucleotide sugar up-expressed significantly,such as dTDP-L-rhamnose, ADP-glucose, dTDP-D-glucose, GDP-β-L-galactose,GDP--D-mannose. In addition, genes in cluster I of glycosyltransferase geneup-expressed significantly, and there genes encoding genes related to polysaccharidetransporter gene and synthase nucleotide sugars gene.The expression of genes related to spore formation: in the nitrogen-free medium,most of the genes involved in spore formation up-expressed, including five regulatorgenes and many structure-forming genes. The five regulators are Spo0A, E, F, K,and G.The expression of genes related to nitrogen metabolism: in the nitrogen-freemedium, genes involved in the pathways of nitrogen metabolism up-expressedsignificantly, including peptide ABC transporter system, catabolic urea pathway (ureABC), catabolic histidine pathway(hut)and arginine catabolic pathway(rocABCDEF). On the other hand,11genes related to ammonia assimilationup-expressed, such as genes rocG and rocG3, however the gene glnA2showeddown-expression by2.7times. It indicates that P. mucilaginosus KNP414can degradevarious amino acids and transferred into glutamic acid as a storage under nitrogenabsent.On conclusion, P. mucilaginosus KNP414can respond to the stress of nitrogenfree through synthesis of polysaccharide, spore formation, and regulation of nitrogenmetabolism, which helps it adapt to many stresses such as nitrogen absent. |
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