Mutation Breeding Of High-yield Arthrospira Strains

Arthrospira is a microalga with high economic value, which is considered the bestfood of the world in21st century by FAO. Arthrospira has been introduced to Chinasince the1980s, after30years of development, cultivation and the related industriesabout Arthrospira have become the largest microalgae biotechnology industries inChina. In the development of Arthrospira cultivation, breeding and utilization of thefine varieties are always be the key point. Mutation breeding is the most commonmethod to screen the new strains with good characteristics, such as fast growth, higherprotein content and so on.In order to obtain stably inherited high yielding Arthrospira strains, nitrosoguanidinemutagenesis and Quizalofop-Ethyl selection were used in this study. Quizalofop-Ethyl,as an acetyl CoA carboxylase inhibitor, affects the fatty acid synthesis by inhibitingacetyl CoA carboxylase activity, then affects the cell growth. Algae cells which canlive under certain Quizalofop-Ethyl concentration generally have a higher acetyl CoAcarboxylase activity, this enhance of activity may come from the change of enzymestructure, the increase of the amount of enzyme expression or enhance of metabolicactivity of the compensatory offshoot. After removed the Quizalofop-Ethyl screeningpressure, the survival algae can get compensatory increase of lipid content and may bethe emergence of new fine varieties.In this study, two stably inherited high yielding Arthrospira strains are obtainedthrough mutagenesis and selection. Compared with the original strain, two mutantshave longer filament and easily gather into clew.Single factor experiments and orthogonal experiments are used to study the optimalculture conditions of the two mutagenic strains and the original strain. The optimalculture conditions of those Arthrospira strains is28℃, pH8.5and light intensity of45mol m-2s-1. Under this optimal culture conditions, growth rate of the twomutagenic strains are67.86%and46.43%higher than that of the original strain;protein content increased1.98%and0.84%; lipid content increased by8.54%and4.88%; and acetyl coenzyme A carboxylase activity increased by31.82%and11.36%.The acetyl CoA carboxylase of original strain and two mutants are studied at themolecular level. Four subunits ORF of acetyl CoA carboxylase are cloned andsequenced. The length of ORF of biotin carboxylase subunit, biotin carboxyl carrierprotein subunits, α-carboxyl transferase subunit and β-carboxyl transferase are981bp,948bp,723bp and536bp respectively. The ORF sequences of the four subunits arehighly conserved and are exactly the same among the original strain, two mutants andArthrospira in Genbank. This result shows that the nitroguanidine mutagenesis do notcause mutations in the ORF sequences of acetyl CoA carboxylase in mutation strains.This paper shows that a combination of NTG with Quizalofop-Ethyl can be used tomutate and screen the Arthrospira strains with high growth rate and high proteincontent, which is important to improve the yield and quality of Arthrospira in industry.