The Regulation Effect And Mechanism Of Antibiotics On Cyanobacteria Oil Production

Due to the exhaustion of fossil fuels and the urgent need for ecological and environmental protection,the development and utilization of new energy sources are increasingly valued by the international market.Biodiesel is considered to be an important alternative to traditional diesel.Biodiesel is a renewable energy project of great concern around the world,and has the advantages of low toxicity,sustainability,and low pollution characteristics.However,there are still difficulties and challenges for the utilization of biodiesel.The most important bottleneck in the promotion of biodiesel is economic benefits.Currently,the commonly used ingredients of catering waste oil on the market are unstable,the cost of development is relatively high and the pollution of waste is large.The raw materials of plant or animal oil can account for more than 70%of production costs.Recent research showed that microalgae cultivation took up less agricultural land and has a higher growth rate compared with crops.The use of microalgae to prepare biodiesel was expected to further save production costs.Among microalgae,cyanobacteria has a bright development prospect,because it can survive under extreme environmental conditions,and the combustion of cyanobacterial biodiesel will produce less sulfide and particulate matter,which is less harmful to human health and the atmosphere.Due to the similarity in cell walls between cyanobacteria and gram-negative bacteria,cyanobacteria may be sensitive to certain antibiotics.Previous studies in our group found that antibiotics had a significant stimulating effect on the growth of cyanobacteria.Based on the above background and research,this article selected a typical biodiesel-producing cyanobacterium,Synechocystis sp.PCC 6803,as research target.The regulatory effects of five typical antibiotics,ciprofloxacin(CIP),amoxicillin(AM),sulfamethoxazole(SMZ),tetracycline(TET)and spiramycin(SPI),on the growth,chlorophyll a content,photosynthetic activity,lipid content and fatty acid composition of Synechocystis sp.PCC 6803 were studies.The main research results and discussions are as follows.Five antibiotics can significantly(p<0.05)stimulate the growth of Synechocystis sp.PCC 6803.The biomass in 100ng L-1 CIP treatment group,AM treatment group,SMZ treatment group,TET treatment group and SPI treatment group were 1.44,1.49,1.5,1.48 and 1.52 times higher than the solvent control group,respectively.Five antibiotics significantly(p<0.05)stimulated the chlorophyll a content and photosynthetic activity parameters(Fv/Fm,rETRmax),indicating that antibiotics can promote the photosynthesis of Synechocystis sp.PCC 6803.Antibiotic exposure induced lipid accumulation in Synechocystis,and the lipid productivity of the five antibiotic treated groups were 2.04,2.29,2.49,2.15 and 1.95 times higher than the solvent control group,respectively.Antibiotics regulated the fatty acid composition of Synechocystis sp.PCC 6803,increased the content of monounsaturated fatty acids and reduce the content of polyunsaturated fatty acids,and improve the combustion performance of biodiesel.Overall,the SMZ treatment group and the TET treatment group have better stimulation effects,so they are selected for subsequent experiments.To further explain the stimulation results of antibiotics on growth and oil production of Synechocystis sp.PCC 6803,the molecular mechanism of sulfamethoxazole(SMZ)and tetracycline(TET)in regulating the oil production performance of Synechocystis sp.PCC 6803 was analyzed by proteomic research The SMZ treatment group and the TET treatment group induced the differential expression of 134 and 11 7 proteins,respectively,with more up-regulated proteins than down-regulated proteins,demonstrating that antibiotic stress would lead to an adaptive response of the Synechocystis sp.PCC 6803.Proteomic results indicated that ribosomal proteins play an important role in the adaptive response of Synechocystis sp.PCC 6803 to antibiotics.Two antibiotics regulated the proteomic expression file of Synechocystis sp.PCC 6803 in a similar pattern.Sulfamethoxazole(SMZ)and tetracycline(TET)can regulate 13 biological processes of Synechocystis sp.PCC 6803,in which proteins related to cell differentiation and division are over-expressed in the SMZ treatment group and the TET treatment group,indicating that antibiotics can stimulate the growth of cyanobacterial cells.Under exposure to sulfamethoxazole(SMZ)and tetracycline(TET),photosynthesis-related proteins in Synechocystis cells were up-regulated,which in turn leads to an increase in the photosynthetic activity of synechocystis sp.PCC 6803,providing energy support for cell growth and lipid synthesis.The responses of the differential proteins indicated that sulfamethoxazole(SMZ)and tetracycline(TET)promoted the accumulation of lipids by inhibiting the catabolism and transport of carbohydrates.Sulfamethoxazole(SMZ)and tetracycline(TET)induced the differential expression of proteins related to cellular substances biosynthesis and adjusted fatty acid composition in Synechocystis sp.PCC 6803.