A Preliminary Study On Acidic PH Stress Responses Mechanisms Of Nematodes

As an essential environmental factor,pH affects many life processes such as growth,development,metabolism,as well as immune regulation.Whether on land or in water,living organisms often experience pH fluctuations.Ocean acidification,acid rain and the resulting acidification of water and soil all lead to a decrease of living environmental pH,which results in a series of negative effects on organisms.At present,the molecular mechanism of how organisms perceive and respond to acidic pH stress is unclear.Therefore,using Caenorhabditis elegans and Marine nematode Litoditis marina as animal models,we find several regulatory mechanism underlying how nematodes response to acid pH stress,through phenotypic experiments and transcriptome analysis.The main discoveries are the following:1.C.elegans has a wide tolerance range to pH(pH 3.13?11.33),but with the decrease of pH,its spawning time is delayed,and in the condition of very low acidity(pH 2.93),it cannot grow and reproduce normally.The pH of NGM is 6.33,thus,pH6.33 is the control group,and pH 4.33,pH 3.13 and pH 2.93 are the acid environment treatment group according to the differences generated by the growth and development phenotype test.Through transcriptome analysis,we find that when the pH drops to 4.33,the expression levels of col,nas,dpy and ptr,which are essential for epidermal synthesis and structural integrity increase.When the pH drops to 3.13,the expression of the metabolism of xenobiotics by cytochrome P450 pathway genes(cyp,gst,ugt,and ABC transporters)and nuclear hormone receptor genes increase.And with the drop of pH,HSP70 and HSP20 genes of C.elegans are down-regulated.2.L.marina has a relatively narrow tolerance range to acid pH stress compared to C.elegans.When the pH drops from 5.92 to 5.33(the optimum growth condition of L.marina is 5.92 in our laboratory),the growth and development rate of L.marina slows down significantly,but it can still reproduce.However,when the pH drops to4.33,L.marina cannot grow into adults.Transcriptome analysis shows that when pH decreases from 5.92 to 4.33,the fatty acid ?-oxidation pathway genes and the unsaturated fatty acid synthesis genes in L.marina are up-regulated.The expression of cuticle related genes show different changes.The expression level of epidermal collagen genes col do not change,and the expression of 2 nas genes and 6 ptr genes are significantly up-regulated.What's more,the expression levels of cytochrome P450 pathway related genes,lectin C genes and heat shock protein HSP70 family genes significantly increase.3.In response to acid pH stress,C.elegans and L.marina have both differences and similarities.Cuticle synthesis and integrity,together with the reprogrammed xenobiotics metabolism by cytochrome P450 pathway are two major stress-responsive pathways for C.elegans in acidic stress environments.However,Marine nematode L.marina's response to the decrease of environmental pH is mainly through the metabolism of fatty acids.And the expression of drug metabolism by cytochrome P450 pathway genes,lectin C genes,cuticle related genes(only the ptr and the nas,no collagen genes)and heat shock protein HSP70 family genes increase in response to low pH environment.C.elegans is able to grow into an adult and reproduce eggs at pH 3.13,while L.marina is unable to grow into an adult at pH 4.33,showing more vulnerable to acid stress.We speculate that the key to this difference is that compared with C.elegans,the cytochrome P450 pathway genes in the genome of L.marina significantly reduce.Thus,the metabolic capacity of toxic substances accumulated in the body due to the physiological disorder caused by the acidic environment is reduced,the body is less acid resistant.The cytochrome P450 pathway may be a key pathway for nematodes to respond to and adapt to extremely acidic environments.The systematic regulation pattern in response to acid pH stress found in nematodes provide a reference for understanding the molecular mechanisms by which organisms can survive in an environment with changing pH environments.Our data might lay the foundation to identify the master gene(s)responding and adaptation to acidic pH stress in further studies.