Isolation And Identification Of Bacteria And Antibacterial Function Study Of Bacteria-specific Lectin In Procambarus Clarkii

Procambarus clarkii,as one of the important aquaculture breeds in China,has become more and more popular with the promotion of spicy crayfish and other delicacies.The aquaculture scale is also increasing year by year.There were a few bacteria in haemolymph of P.clarkii,some of which were opportunistic pathogens.When the body’s defenses are weakened,the large number of bacteria in the body can easily cause the death of P.clarkii and large group infection,which causing serious losses to the aquaculture industry.Therefore,understanding the potential pathogenic bacteria in P.clarkii is not only improve the efficiency of disease prevention,but also can carry out targeted treatment when the disease occurs,so as to minimize economic losses.The improper use of antibiotics leads to the emergence of drugresistant bacteria,which makes the prevention and control of aquatic animal diseases more difficult.It can alleviate the problem of bacterial resistance by researching new antibacterial molecules.P.clarkii,an invertebrate,mainly relies on innate immunity to resist pathogen invasion.As a pattern recognition receptor,C-type lectin plays an important role in the immune response.To elucidate the role of C-type lectin in the anti-bacterial immunity of P.clarkii could provide effective basis for the prevention and control of shrimp and crabs.In order to take preventive measures,the bacteria in P.clarkii were cultured and 39 strains with obvious morphological differences were screened,which were divided into 15 genera by 16 S r RNA sequencing.There were 11 strains of Citrobacter.5 strains of Aeromonas;4 strains of Enterobacter and Exiguobacterium respectively;2 strains of Shewanella and Acinetobacter respectively;One strain of Klebsiella,Proteus,Lactococcus,Lysinibacillus,Vibrio,Kluyvera,Macrococcus and Morganella.These results provide some reference for disease prevention and control of P.clarkii.In this study,a C-type lectin（Pc Lec E）was screened from P.clarkii.By analyzing the bacterial diversity in the haemolymph of P.clarkii,it was found that Pc Lec E could specifically reduce the proportion of Enterobacter and Mycoplasma in the haemolymph of P.clarkii.Pc Lec E is constitutively expressed in P.clarkii and responds to E.cloacae stimulation.Pathological section analysis showed that Pc Lec E could attenuate intestinal damage caused by E.cloacae in P.clarkii.Further studies showed that Pc Lec E promoted phagocytosis and clearance of E.cloacae by hemocyte and inhibited the proliferation of E.cloacae in vitro.After the interference of Pc Lec E in P.clarkii,the elimination ability of E.cloacae was reduced,and the mortality of shrimp increased after the bacterial stimulation.Pc Lec E may protect P.clarkii from the damage of Enterobacter by inhibiting bacteria and promoting phagocytosis of bacteria by hemocyte,which also provides strong candidate data and theoretical support for the development of Enterobacter specific drugs.