Abstract
BackgroundSulfur-deprived cultivation of Chlamydomonas reinhardtii, referred as “two-stage culture” transferring the cells from regular algal medium to sulfur-deplete one, has been extensively studied to improve photobio-H2 production in this green microalga. During sulfur-deprivation treatment, the synthesis of a key component of photosystem II complex, D1 protein, was inhibited and improved photobio-H2 production could be established in C. reinhardtii. However, separation of algal cells from a regular liquid culture medium to a sulfur-deprived one is not only a discontinuous process, but also a cost- and time-consuming operation. More applicable and economic alternatives for sustained H2 production by C. reinhardtii are still highly required.ResultsIn the present study, a significant improvement in photobio-H2 production was observed in the transgenic green microalga C. reinhardtii, which employed a newly designed strategy based on a heat-inducible artificial miRNA (amiRNA) expression system targeting D1-encoded gene, psbA. A transgenic algal strain referred as “amiRNA-D1” has been successfully obtained by transforming the expression vector containing a heat-inducible promoter. After heat shock conducted in the same algal cultures, the expression of amiRNA-D1 was detected increased 15-fold accompanied with a 73% decrease of target gene psbA. More interestingly, this transgenic alga accumulated about 60% more H2 content than the wild-type strain CC-849 at the end of 7-day cultivation.ConclusionsThe photobio-H2 production in the engineered transgenic alga was significantly improved. Without imposing any nutrient-deprived stress, this novel strategy provided a convenient and efficient way for regulation of photobio-H2 production in green microalga by simply “turn on” the expression of a designed amiRNA.
Highlights
Sulfur-deprived cultivation of Chlamydomonas reinhardtii, referred as “two-stage culture” transferring the cells from regular algal medium to sulfur-deplete one, has been extensively studied to improve photobioH2 production in this green microalga
It was reported that a copper responsive inducible chloroplast expression system targeting Nac2 protein, which is required for the stable accumulation of the psbD mRNA encoding the D2 reaction center polypeptide of photosystem II (PS II), can be used to turn off PS II activity and thereby impose a potential for hydrogen production in C. reinhardtii [12]
Since the turnover of D1 protein in PS II complex of C. reinhardtii has been confirmed to be correlated with the improved H2 yield by the sulfur-deprivation method, we proposed here a new strategy on regulation of photobioH2 production by C. reinhardtii
Summary
Sulfur-deprived cultivation of Chlamydomonas reinhardtii, referred as “two-stage culture” transferring the cells from regular algal medium to sulfur-deplete one, has been extensively studied to improve photobioH2 production in this green microalga. During sulfur-deprivation treatment, the synthesis of a key component of photosystem II complex, D1 protein, was inhibited and improved photobio-H2 production could be established in C. reinhardtii. The implementation of sulfur-deprivation technique needs laborious downstream process, such as cost- and timeconsuming of separation of algal cells from a regular liquid culture medium to a sulfur-deprived one. Obviously this method was not a continuous process. More applicable and economic ways for the practice are still highly required [13]
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