Correlationship Between Heat Acclimation And Intestinal Bacterial Composition

ObjectiveEnvironmental heat exposure or strenuous physical activities could induce heat stress,thus cause heat illness,which is composed by a continuum from heat exhaustion,heat injury to heat stroke.Heat stroke is the most severe stage of the heat illness,normally accompanied by a dysfunction of central nervous system and a progressive multi-organ damage,even death.Heat acclimation is defined as physiological changes that could improve one’s adaption to heat stress induced by long-term repeatedly heat exposure,and it is recognized as the most effective method to prevent the onset of heat stroke.Moreover,it is reported that experimental animals fed with known probiotics have a better ability to deal with heat stress,accompanied by a modulation of intestinal microbiota,so maybe gut microbiota could also play a role in regulating heat tolerance.Thus,the objective of this research is to investigate the relationship between heat acclimation with the composition of gut microbiota,and find out taxa that has the potential to accelerate the progress of heat acclimation.MethodsA model of heat acclimation was built with rat by repeatedly exposed to heat,and weight of rats were recorded before and after heat exposure.Fecal samples were collected before exposure and rectal temperature as well as time of exposure were also recorded during the exposure;Physical indicators such as height,weight,resting body temperature,heart rate and other physical indicators were measured in the state of naturally heat acclimation and deacclimation of the same people population,and an exercise ability test was carried out after collecting fecal samples,and the body temperature after exercise was recorded;DNA was extracted from fecal samples collected before and then amplified with specified V3~V4 16 S r DNA primers,after which being high-throughput sequenced,with which the alpha,beta diversity analyses were carried to find out whether there stand differences in gut microbiota flora between groups,after which LDA effect size analysis were adopted to find out the taxa that correlated to the compositional differences between groups.Pearson correlationship analysis was applied to investigate the correlationship between taxa acquired by LDA effect size analysis and co-occurrence network analysis was carried out to research the topology of gut microbiota network.ResultsCharacters of heat acclimation were induced by repeatedly heat exposure in rats;alpha diversity indexes showed no significant difference between intestinal microbiota in rats after heat acclimation and;significant differences were observed in PERMANOVA based on Bray-Curtis distance and unweighted-Unifrac distance(p<0.05),but with weighted-Unifrac distance there was no difference of significant observed;Lactobacillus was identified as heat acclimation-related taxon;A strong positive correlation between Intestinimonas and Lactobacillus was observed(r=0.91);Different genus of Muribaculaceae showed opposite effects on heat acclimation;no taxa of network hub was observed.Positive correlations within the intestinal bacterial population increases after the formation of heat tolerance,meanwhile negative correlations decrease.The alpha diversity indexes of intestinal bacteria get higher after deacclimation;There is no significant difference observed between groups based on Bray-Curtis distance and weighted Unifrac distance in a multivariate permutation analysis;multivariate permutation analysis based on unweighted Unifrac distance reveals significant differences(p<0.05)in the composition of intestinal bacterial communities between groups,indicating a difference in the composition of gut microbiota appears;Genus Romboutsia and the Clostridium sensu stricto 1 play important roles in the composition of intestinal bacterial communities in a heat-acclimated state,but the correlation between characteristic classifications is weaker compared to that in experimental animals;no network hub was found within the intestinal bacterial communities in both groups,and no negatively correlated relationships meeting the selection criteria were observed in either groups.The positive correlation within the intestinal bacterial population increases after the formation of heat tolerance.Conclusions1.The alpha diversity of intestinal bacterial communities would be significantly lower after heat acclimation: In experiments on animals,the alpha diversity,described by indexes indicating richness,diversity and evenness of the distribution of intestinal bacteria,shows a trend of descending;While in researches on human beings,it was observed that after the population get acclimated to heat naturally,compared with after deacclimated,alpha diversity indexes of intestinal flora showed significant reductions.2.Significant changes happen to the composition of intestinal bacterial communities after heat acclimation: In both parts,the results of PERMANOVA based on unweighted-Unifrac distance showed significant difference,suggesting that there were differences in the composition between groups with different heat tolerance abilities.3.Lactobacillus,Romboutsia and Clostridium sensu stricto 1 may be key taxa who play huge in heat acclimation,and this effect may be achieved by the production of short-chain fatty acids such as acetic acid and butyric acid as their met: In animal experiments,it was observed that Lactobacillus was associated with the achievement of heat tolerance through heat acclimation;In experiments carried on human body,Romboutsia and Clostridium sensu stricto 1 were identified as associated with heat acclimated status.Literatures suggest that above-mentioned taxa can produce short-chain fatty acids as their met,and short-chain fatty acids have a protective effect on intestinal wall cells in a hot environment by performing as energy sources,which may be the mechanism of these taxa in promoting heat acclimation.4.Intestinimonas may participate in the progress of heat acclimation through interactions with Lactobacillus: It was found that Intestinimonas showed a strong positive correlation with Lactobacillus,but it was not classified as a taxon related with heat accliamtion in LEf Se analysis.Its role in the formation of heat-tolerant-related gut microbiota phenotype remains to be investigated.5.Number of synergistic effects between gut microbiota taxa grew while that of antagonistic effect shrink after heat acclimation: In experiments on animals it was observed that number of pairs of positive correlationship ascend while that of negative ones descend and a grow was also observed in number of positive pairs between intestinal bacteria taxa in the research on human beings.