| Chromium(Cr)pollution has always been the focus of environmental control.Among them,hexavalent chromium(Cr(Ⅵ))pollution brings serious ecological risk to people’s life safety.Procambarus clarkii has strong environmental tolerance.Crayfish still survive and breed in waters contaminated with hexavalent chromium.Through survival rate experiments,it was found that after injection of 10 μl of 100 mg/L Cr(Ⅵ)for 192 h,the survival rate of crayfish was 90%,indicating that it had a certain chromium tolerance.m RNA sequencing analysis showed that 2,937 genes of crayfish were differentially expressed under Cr(Ⅵ)stimulation.Among them,2,454 genes were up-regulated and 483 genes were down-regulated.This indicates that Cr(Ⅵ)stimulation affects the transcription process of crayfish.By analyzing the polymorphisms of crayfish flora,it was found that the hemolymph flora of crayfish changed significantly after Cr(Ⅵ)stimulation.Hemolymphatic bacteria were co-incubated with Cr(Ⅵ),and the content of Cr(Ⅵ)decreased significantly after 24 h.To investigate the role of hemolymph microflora in Cr(Ⅵ)stimulation of crayfish,pathological changes of hepatopancreas and intestinal tissues were analyzed.It was found that the degree of damage of Cr(Ⅵ)to the hepatopancreas and intestinal tissues by Cr(Ⅵ)was significantly increased after the removal of hemolymph flora.The detection of malondialdehyde and antioxidant enzyme indexes showed that the content of malondialdehyde in the hepatopancreas increased significantly after the removal of hemolymphoid flora,and the activity of antioxidant enzyme was significantly reduced.This shows that the hemolymph flora in crayfish plays an important role in helping the host resist Cr(Ⅵ)damage.It has been found that Exiguobacterium in hemolymph has a strong ability to repair Cr(Ⅵ).The mode of repairing Cr(Ⅵ)by Exiguobacterium was studied using H6 strain as the model.Through subcellular component analysis of H6 strain,it was found that H6 strain does not rely on strain adsorption or secretion products to repair Cr(Ⅵ).m RNA sequencing and q PCR analysis showed that the expression levels of ATP-bindingcassette(ABC)transporter family genes and oxidoreductase genes in H6 strains were significantly increased after Cr(Ⅵ)stimulation,and the ABC transporter family may provide a basis for H6 strains to survive under Cr(Ⅵ)stress.The oxidoreductase enzyme in the H6 strain reduces Cr(Ⅵ)to trivalent chromium(Cr(III)),in which the nfs A may play a strong role.During the experiment,stimulation of Cr(Ⅵ)was found to slow down the ovary development of crayfish.The pathological section analysis of ovarian tissue showed that the volume of egg cells decreased after Cr(Ⅵ)stimulation,the development of egg cells stagnated,and the content of lipid in egg cells decreased significantly.The content of vitelline protein and the expression of vitelline protein decreased significantly,and the MDA detection showed that the degree of lipid oxidation in egg cells was aggravated.This was slowed by supplementation with H6 strains and nfs A-carrying recombinant strains.It was shown that Cr(Ⅵ)affects ovary development of crayfish,and supplementation with H6 strains and nfs A-carrying recombinant strains will slow this effect.To verify the feasibility of H6 strains in other animals,supplementation with H6 strains in mouse guts can also slow down intestinal damage caused by Cr(Ⅵ).Experiments have shown that hemolymph flora is one of the reasons why crayfish can survive in Cr(Ⅵ)contaminated environments.Exiguobacterium has a strong ability to reduce Cr(Ⅵ)to Cr(III).The supplementation of Exiguobacterium H6 can help the host resist Cr(Ⅵ)stress and reduce the damage caused by hexavalent chromium.Exiguobacterium H6 can be used as a microecological preparation to alleviate the toxicity caused by Cr(Ⅵ)pollution. |
