Benzoic Acid Promotes Chlorella To Synthesize Trinexapac-ethyl And Regulate Cell Metabolisms

Microalgae are capable of converting light energy and CO₂ into biomass energy and resources.Phytohormones are small-molecule signaling substances that have been detected in the environment of algae in recent years and are capable of significantly regulating the vital activities of microalgae,which have great potential to enhance microalgal biomass production.Benzoic acid and its derivatives are a classical phytohormone.However,the regulatory effects of benzoic acid as a phytohormone are mostly confined to higher plants,but the mechanisms of its effects on the growth of microalgae and its mediated algal biomass synthesis are rarely reported.In this paper,we investigated the effects of benzoic acid on the growth of microalgae and the pathways and mechanisms of its mediated synthesis of biomass resources by using benzoic acid as the research object and the synthesis of high value-added products of microalgae as the main line.First,the effects of benzoic acid on the growth and biomass synthesis of microalgae were investigated.The results showed that the cell density of Chlorella increased by15.0%,and the utilization of total nitrogen and total phosphorus increased by 15.5%and 10.8%,respectively,under the effect of benzoic acid.The results of photosynthetic efficiency test showed that benzoic acid promoted photosynthesis of microalgae,which increased photosynthetic pigment content by 11.2%and carotenoid content by 12.4%.Benzoic acid also contributed to a 13.2%increase in protein content,24.8%and 40.0%increase in oil and grease yield,respectively,and an increase in the composition of saturated fatty acids C16-C18,which are precursors to higher quality biodiesel.Secondly,benzoic acid was found to promote the synthesis of the high value-added product trinexapac-ethyl(TE),which is the first time that TE was detected in microalgae.50?g/L benzoic acid stimulation resulted in 10.6 ng/L of TE in Chlorella and 4.4 times higher yield than the control.TE(10^-5 mol/L)significantly promoted the growth rate of Chlorella vulgaris and increased its oil production and yield by 106.7%and 255.1%,respectively.The biosynthesis pathway of TE is as follows:benzoyl coenzyme A is produced by acyl coenzyme A synthase,then cyclohexa-1,5-diene-carbonyl-Co A is produced by reductase,after which cyclohexa-1,5-diene-carbonyl-Co A is Converted to 6-hydroxycyclohex-1-ene-1-carbonyl-Co A by hydratase,then 6-oxocyclohex-1-ene-1-carbonyl-Co A is produced by dehydrogenase,and finally 6-oxocyclohex-1-ene-1-carbonyl-Co A is produced by dehydrogenase.carbonyl-Co A,and finally catalyzed by hydrolase and carboxylase enzymes to produce 4-carboxylic acid-2-6-cyclohexanedione-1-carbonyl-coenzyme A,and cyclopropane amino acids in the action of dimethylaminopyridine isoenzymes to produce TE.Finally,the effect of benzoic acid on the metabolic regulation of Chlorella vulgaris was probed.Benzoic acid was found to drive the synthesis of growth hormones and cytokinins,with significant promotion effects mainly on five species:6-benzylaminopurine(6-BA),kinetin(KT),indole butyric acid(IBA),cinnamic acid(RGS)and TE.The production and secretion of these growth hormones and cytokinin-like phytohormones promoted the signaling pathway,improved the photosynthetic efficiency of microalgae,and enhanced the accumulation of material in microalgae cells;meanwhile,they promoted the TCA cycle and oxidative phosphorylation process in algal cells,synthesized large amounts of ATP,and provided energy for the growth and development of Chlorella;promoted the DNA replication of Chlorella,and provided the genetic material basis of Chlorella.In summary,it was found that benzoic acid stimulated the synthesis of TE in Chlorella cells,promoted the synthesis and metabolic pathway regulation of various hormones in Chlorella cells,and increased the cell density and biomass resource production of Chlorella.