| In recent years,the outbreak of Heterosigma akashiwo(H.akashiwo)red tide has been frequent in coast and estuary areas of China.The outbreak of red tide not only seriously damaged the local coastal ecosystem,but also affected related industries such as fisheries,aquaculture and tourism.This experiment is based on the previous research of my team which isolated a novel marine bacterium from algal bloom estuary(Pearl river,China),and identified as Bacillus sp.B1.In this paper,we studied the algicidal effects of extracellular algicidal compounds(EACs),extracted from Bacillus sp.B1,against H.akashiwo and its physiological and metabolome response the extracellular algae-dissolving crude extracts(EACs)secreted by B1 against red tide.Algal physiology changes and metabolic response.The specific research results are as follows:(1)EACs had a significant growth inhibitory effect on H.akashiwo,showing a dosedependent manner,but the inhibitory effect in the short term was not obvious,but with the increase of exposure time,after 96 hours,more than 93% of algae are inhibited,so the acute lethal effect of EACs on H.akashiwo is not obvious,but it has a strong destructive effect on the viability of algal cells with time.(2)In addition,different EACs stress also affected the physiological activity and morphological size of H.akashiwo.Increased levels of reactive oxygen species(ROS) in cells may be related to the blockage of the electron transfer rate chain of photosystem ? and the depletion of cellular antioxidant enzymes.The increase of the maximum photosystem ? I quantum yield(Fv/Fm)inhibition and the decrease in nonphotochemical quenching indicated a decrease in the photosynthetic performance of the cell and a reduction in the ability of the photosystem to handle the accumulation of excess energy(NPQ).Changes in photosynthetic pigments indicated that low concentrations of EACs have no effect on chlorophyll a,chlorophyll c and carotenoids,however,medium and high concentrations of EACs have inhibitory effects on the three pigments,indicating that the chloroplast is destroyed,which in turn leads to a reduction in photon absorption efficiency and to the subsequent photochemical processes.(3)Esterase activity and Fv/Fm are commonly used as indicators to measure the physiological activity of algae cells under environmental stress.Dose-response curve(DRC)and relative potency(RP)were used to evaluate the response speed(sensitivity)of Fv/Fm and esterase activity inhibition under differential EACs stress,and proved that the applicability of DRC and RP were good fit in algal action model and can be used to assess the sensitivity of different physiological indicators.This will provide a practical tool for studying the physiological function of algae and the toxicological response of algae under environmental and pollutant stresses.(4)Using metabolomics to study the effects of EACs on metabolites and metabolic pathways of algae from a molecular perspective,28 differential metabolites were identified,which involved photosynthesis,antioxidant enzyme synthesis,cell penetration and signal transduction and amino acid transport.The inhibition of porphyrin and chlorophyll synthesis indicated the inhibition of photosynthetic pigments synthesis,resulting in the reduction of cytochromes such as chlorophyll a,chlorophyll c and carotenoids;the increase of glutathione metabolism marked the promotion of antioxidant enzymes synthesis,which cope with the increasing of ROS;the decrease of alcohols such as glycerin,mannitol and inositol indicates the decrease of sugar synthesis,which affects the subsequent cell carbohydrate metabolism and the imbalance of cell membrane osmotic pressure.In addition,EACs also induced the inhibition of fatty acid metabolism. |
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