Cultivatin Of Synechococcus Sp.for CO₂ Fixation And Laminarinase Production

The CO₂ emissions from the burning of fossil fuels cause detrimental changes to the earth's climate.Cyanobacteria have demonstrated potential for CO₂ fixation,because they have the advantage of high growth rate and CO₂ fixation rate,as well as co-production of high value biologically active products.In this research,the objectives were to heterologous express LamAgene from Thermotoga maritima MSB8 in a bioengineered Synechococcus sp.PCC 7002 and high concentration CO₂ capture by the recombinant Synechococcus sp.7002.The specific enzyme activity and characteristic of the recombinant laminarinase were investigated based on the successful construction of recombinant Synechococcus sp.PCC 7002 strain.The maximal laminarinase enzyme activity was found to be 4.325 U·mg-1 dry mass,observed at pH 8.0 and 70?.The enzyme retained 85% of its maximal activity between pH 7.0 and 8.5.Meanwhile,the recombinant laminarinase was a thermo-tolerant-glucanases enzyme,which showed a half-life of 40 min and 20 min at 80 and 90? ?.According to the advantage and disadvantage of closed photobioreactor,an advanced continuously stirred tank photobioreactor was designed and used for cyanobacteria cultivation.The reactor kinetics and characteristic of cyanobacteria growth were investigated with the control experiments and full factorial design.The major factors of Xmax are light intensity > CO₂ concentration >temperature*temperature>temperature>light intensity;the major factors of ?max are CO₂ concentration>light intensity>temperature.A maximum biomass concentratin?3.929 g·L-1?and a maximum specific growth rate were achieved at 0.5 L·min-1 air input?5% CO₂?,300 ?mol·m-2·s-1 light intensity and 30??Otherwise,the photoperiod can affect the growth rate,biomass productivity,CO₂ fixation rate and maximum biomass concentration.High CO₂ concentration had significant inhibiting effect on the mutant strain and laminarinase production.Although the mutants can tolerate the 15% CO₂ concentration,the Xmax,?maxandspecific enzyme activity decreased 36.9%,40.7% and 75.1%,respectively,compared with 5% CO₂ aeration.The Xmax and ?max of mutant strain cultivated with 15% CO₂ were significant increased by pH control and domestication with gradually increased high CO₂ concentration.The results of pH control method,the culture with Carbonate-Bicarbonate Buffer?pH 8.0?showed best result compared with other buffer.The Xmax and ?maxincreased 33.3% and 15.8%,respectively,compared with control mutant strain.But as a result of increase of pH,the CO₂ fixation efficiency decreased consequently.The Xmax and ?max of the first generation cultivated with gradually increased high CO₂ concentration increased 24.4% and 11.2% compared with control mutant strain.Furthermore,after N generation,the mutant strain could well-adapt the high CO₂ concentration.