Studies On The Occurrence Of Extrachromosomal DNA From Arthrospira And The Structure And Function Of Relative Genes

Arthrospira is an economically important commercial cyanobacteria, of which the study of molecular genetics lag behind relatively. The completion of whole genome sequencing and construction of morphology are hot issues of Arthrospira research. In this article we focus on the extrachromosomal DNA (exDNA) of Arthrospira. By inspecting the occurrence of exDNA under the platform of experimental biology and bioinformatics, structure and function of the relative genes were explored. The main contents were shown as following:(1) Arthrospira strains multimorphologically were collected from various resources and single filaments were picked with the serial dilution method and the micropipette separation leaving pure culture system of18strains were constructed. Combining morphological observation under optical microscope with16S rRNA-ITS sequences as a molecular marker, relative genes sequencing and phylogenetic analysis were conducted. The results indicate that tested strains were all Arthrospira platensis, including the ones from4microalgal companies, which confirm that commercial Spirulina is Arthrospira according to biolgical classification.(2) Six protocols for extraction of whole genome DNA of the Arthrospira strains were comparatively studied and the method of Freezing-thawing CTAB is effective in extracting not only chromosomal but extra-genomic DNA from the tested strains. We found7strains containing exDNA, which in a form of covalently closed circular, were widely distributed in Arthrospira strains and showed steady heredity character and were related with certain phenotype changes between filamentous cyanobacteria mutants. The difference of exDNA between various morphological mutants showed their relationship with the construction of morphology.(3) Twenty-four exDNA-related genes were identified, each of which has only one homologue with high identity in different whole genome sequencing drafts. Similar conserved motifs and amino acids showed that exDNA from Arthrospira contain four type of domain: GGDEF, GAF, PAS and HATPase_c, which may function as signal transduction molecules during environmental response in cyanobacterium.(4) The study on the function of exDNA-related genes indicated that:exDNAs from Arthrospira J12occur steadily during the whole growth phage of which the relative quantity pattern of the related genes vary according to the genes; under the condition of0-60mg/L Pb2+concentration, Arthrospira CG occur steadily and interestingly we found that gene SS1maybe related to the tolerance of heavy metal in Arthrospira.