Study On The Algicidal Mechanism Of Brevibacillus Laterosporus Based On Omics

The frequent occurrence of cyanobacteria blooms caused severe economic losses to aquaculture and damage to water ecological environment.Algicidal bacteria are a group of bacteria that can kill or inhibit algae and are expected to provide effective biological control of water blooms.As the advantages of high efficiency,environmentally friendly and strong specificity,algicidal bacteria have great significance and broad prospects in regulating water quality and controling of cyanobacteria..In this study,the algicidal mechanism of Brevibacillus laterosporus Bl-zj on Microcystis aeruginosa was studied.Combined analysis of physiological and biochemical indexes,microbial diversity,genome and transcriptome was performed,to revealed the algicidal mechanism in molecular levels.This study will provide theoretical basis for the control of water bloom.1.B.laterosporus Bl-zj had a strong algae-lysing effect on M.aeruginosa.At the4^thday,the removal rate of M.aeruginosa in the 1:1 group was 89.54%.Scanning electron microscopy（SEM）showed that,at the 4^thday,the surface of the algal cells was sunken,the cells were deformed and mucous material was produced on the surface.Moreover,the addition of Bl-zj significantly reduced the diversity of the interalgal bacterial community of M.aeruginosa and destroyed the structure of the community.2.The genome of B.laterosporus Bl-zj was sequenced and analyzed,and 34potential algicidal genes were screened out,including 8 virulence factors,18 secretion proteases and 8 antibiotic resistance genes,such as toxin ETX,lethal factor,glycoside hydrolase family 18,peptidase M23 family protein,chitinase,multidrug ABC transporter ATP-binding protein,beta-lactamase,efflux transporter and so on.These genes may play important roles in host recognition,invasion and destruction of algal cells.3.Transcriptome sequencing analysis of B.laterosporus Bl-zj co-cultured with M.aeruginosa for 2^ndand 4^thdays were conducted.The results showed that,the differentially expressed genes（DEGs）were mainly enriched in the pathways of carbohydrate metabolism,amino acid metabolism,energy metabolism and lipid metabolism in the algicidal process.Among them,the DEGs related to xenobiotics biodegradation and metabolism and the other secondary metabolites biosynthesis pathway were mainly up-regulated.In addition,the DEGs related to valine,leucine and isoleucine degradation,fatty acid degradation,ABC transporter,hydrolase and protease and some antibiotic biosynthesis genes（such as prodigiosin biosynthesis,etc）were mainly up-regulated,while the ribosome related genes were down-regulated.The results showed that,Bl-zj could resist microcystins and inhibit the growth of microalgae by synthesizing a large number of energy substances for its own growth and material transport,and secreting a variety of antibiotics,proteases and chitinase and other secondary metabolites to achieve the effect of algae-lysing.4.Transcriptome sequencing analysis of M.aeruginosa co-cultured with B.laterosporus Bl-zj for 2^ndand 4^thdays were conducted.The results showed that,in the co-cultured group,the expressions of genes related to photosynthesis and oxidative phosphorylation were mainly down-regulated,while the genes related to fatty acid synthesis were mainly up-regulated.In addition,the expression of the antioxidant enzymes,such as 2-Cys peroxiredoxin was increased.The inhibition of photosynthetic system and oxidative phosphorylation,which are important processes of electron transport and energy generation in algal cells,affects the energy acquisition of algal cells,while the up-regulation of fatty acid synthesis related genes and antioxidant enzymes indicates that the algal cells are in a state of oxidative damage.By destroying the bacterial community of M.aeruginosa and secreting algae-lysing substances such as antibiotics and proteases to act on M.aeruginosa,B.laterosporus Bl-zj could inhibit the photosynthetic system and oxidative phosphorylation of algal cells,so that the algae cannot produce enough energy to maintain the survival needs,resulting the oxidative damaging and lipid peroxidation,eventually leading to the death of algae.