The New Varieties Breeding Of Low Temperature Tolerant Arthrospira

The filamentous Cyanobacterium Arthrospira has been produced commercially around the world,and is recognized as a functional health-care food and high-value product.However,because most commercial Arthrospira strains are from mesophilic Arthrospira platensis and Arthrospira maxima with the optimal growth temperature between 35°C and 38°C,and the minimal temperature of mesophilic Arthrospira that was allowed to grow was approximately 18°C,many temperate regions are not able to overcome the temperature limits imposed on industrial cultivation normally from late autumn to early spring.For broadening cultivation geography and extending cultivation time on commercial Arthrospira,we screened and segregated 5 low temperature and low light intensity resistant strains of Arthrospira sp.?GMPA1,GMPA7,GMPB1,GMPC1,and GMPC3?produced by Ethyl methanesulfonate?EMS?mutagenesis and low temperature screening.The 5 Arthrospira strains can grow rapidly below 14°C,43.75?mol photons m^-2·s^-1 and perform breed conservation at 2.5°C,8.75?mol photons m^-2·s^-1.Morphological identification and the sequence analysis of 16S rRNA and internally transcribed spacer?ITS,16S-23rRNA?,GMPA1,GMPA7,GMPB1 and GMPC1 were identified as Arthrospira platensis,while GMPC3 was Arthrospira maxima.By measuring dry biomass at regular intervals to evaluate the growth at different culture temperatures,the 5 strains showed that the maximum dry biomass production and the average dry biomass productivity of GMPA1,GMPB1,and GMPC1 are 2057±80 mg·l^-168.7±2.5mg·l^-1·d^-1,1839±44mg·l^-1 60.6±1.8mg·l^-1·d^-1,2113±64 mg·l^-177.7±2.5 mg·l^-1·d^-1 respectively at 16°C 43.75?mol photons m^-2·s^-1.To further examine the low temperature tolerance and the growth temperature preference,GMPB1 was chosen for studies in 20 L transparent polypropylene container in winter and in summer.The results showed that GMPB1 grew well below the average temperature of 10°C,achieving 3258 mg dry biomass from initial 68 mg in winter;and GMPB1 grew rapidly above the average temperature of 28°C,achieving 1140 mg·l^-1 dry biomass from initial240 mg in summer.In addition,the analysis of nutritional content of GMPB1 showed phycobiliproteins and carotenoids at normal levels.Arthrospira metabolism relates to terpenoids,and the methyl-D-erythritol4-phosphate pathway?MEP?is the only terpenoid biosynthetic pathway in Cyanobacteria.The 1-deoxy-D-xylulose 5-phosphate reductoisomerase?DXR?gene from GMPB1 was cloned and the phylogenetic analysis displayed GMPB1 is closest to Cyanobacteria Oscillatoria nigro-viridis PCC711.In addition,the phylogenetic analysis offers a credible support for the endosymbiotic hypothesis of Cavalier-Smith.In order to further validate and discuss the MEP pathway and endosymbiotic hypothesis,we choose pyropia haitanensis as experimental material to study the MEP pathways and discuss the evolutionary relationships about different algae in the appendix.