Sequencing And Analysis The Whole Genome Of The Arthrospira Platensis Agb-ap02

In the article, the whole genome of the alkaliphilic cyanobacterium Arthrospira platensis AGB-AP02 was sequenced by high throughoutput sequencing technology for deciphering its unique biological character at the molecular level.2,1463,733 reads were generated, which consist of 1609.78 Mb and covers the whole genome about 292 times. After assembly 91 scaffolds comprising of 5,520,311 bp were obtained,50% of which is above 143,024 bp. And the average GC% of genome is 44.38%. The ORFs in the genome were predicted by Glimmer 3 and the result shows that there are 5989 ORFs discovered with average length of 784 bp. All the ORFs were subjected to database nr,nt,KEGG and COG for annotation and it is demonstrated that 4342,2732,4886 and 3379 ORFs show significant similarity to the proteins registered in the four database respectively. Arthrospira platensis AGB-AP02 lives in the environment where the concentration of carbonate and bicarbonate is very high. From those ORFs the whole pathway of CO2 concentrating mechanism (CCM) was discovered. Those ORFs include operon coding carboxysome, operon coding HCO3- transporters and operon coding CO2 transporters. In the genome the typical CAs with catalytic activity is not discovered and theγ-CA newly discovered in the genome probably plays the role of CA in the cell.Those genes are important molecular base of its adaptation to special Ci environment. Also, Arthrospira platensis AGB-AP02 lives in the environment where the pH is about 9-10. In the genome there are totally 29 ORFs related to the regulation of pH in the cell.Those genes code Na+/H+ antiporter,ABC-type oligopeptide transport system-related subunits,ABC-type dipeptide transport system-related subuni,ABC-type dipeptide/oligopeptide/nickel transport system-related subunits and ABC-type branched-chain amino acid transport systems-related subunits respectively. It is inferred that those 29 ORFs are important molecular base for its adaptation to high akalinity.The molecular mechanism of its adaptation to the high alkalinity is similar to the situation in the Oceanobacillus iheyensis. Arthrospira platensis AGB-AP02 can live in the envivonment of high salinity and be domesticated to adapt to the seawater.Comparative genomic analysis between Arthrospira platensis AGB-AP02 and Trichodesmium erythraeum IMS101 shows that the two species use similar strategy to regulate the osmotic pressure in the cell.One way is involved in the transporters located in the membrane such as Na+/H+ antiporter,Ca2+/Na+ antiporter and K+ transporter and another way is related to synthesis and transporting of proline. Within the ORFs uniquely taken by the Arthrospira platensis AGB-AP02 the key gene-trehalose-6-phosphate synthase invovled in the synthesis of trehalose is discovered and it is infered that Arthrospira platensis AGB-AP02 has the potential to synthesize the trehalose to tolerate the high salinity, which is different from the situation in the Trichodesmium erythraeum IMS101.Analysis towards its metabolism of polyunsaturated lipid acid shows that there exists the integral pathway of synthesizing theγ-Linolenic acid in the Arthrospira platensis AGB-AP02.Those ORFs code acetyltransferase,3-oxoacyl-[acyl-carrier protein] reductase,3R-hydroxymyristoyl ACP dehydrase,enoyl-(acyl carrier protein) reductase,stearoyl-CoA 9-desaturase,fatty acid desaturase(delta 12)and acyl-lipid desaturase(delta 6). However there is lack of key enzyme coding DesB for synthesis of the a-Linolenic acid which is precursor of EPA and DHA, that shows Arthrospira platensis AGB-AP02 can not synthesize the EPA and DHA.Compared to Synechocystis pcc 6803 where only one ORF coding HNH endonuclease and one ORF coding modification methylase were discovered,19 ORFs coding HNH endonuclease and 27 ORFs coding RM system exist in the genome of Arthrospira platensis AGB-AP02.It is inferred that those genes contribute to the unstable genetic transformation system of Arthrospira platensis AGB-AP02. Arthrospira platensis AGB-AP02 and Arthrospira maxima CS-328 shared 3352 similar ORFs and took up special 2637 ORFs and special 3126 ORFs respectively. Furthermore, the structural comparison between Arthrospira maxima cs-328 and Arthrospira platensis AGB-AP02 demonstrated that there happen inserting and inverting accidents during the course of divergence between the two species.The comparison of ORFs between those two species shows that divergence is probably involved in the existence of large number of genes coding retron-type reverse transcriptases and transposases.