Response Of The Gut Microbes Of Apis Mellifera To Two Exogenous Toxicants And Their Protective Effect On The Host

The honey bee(Apis mellifera)is a important pollinator and economic insect worldwide.However,the survival of honey bees has been seriously threatened in recent years,with a clear trend of declining honey bee populations.Among them,the coercion by exogenous toxic substances may be one of the important reasons for the population decline.Gut microbes are a group of microorganisms that inhabit the host gut and play an important role in the digestion and absorption of food,host development,immunity enhancement,pest resistance and reproduction.Currently,gut microbes have been found in many insects to also help protect the host against exogenous toxicants.However,the role played by honey bee gut microbes after host exposure to exogenous toxicants has been little studied.To gain insight into the role of honey bee gut microbes in response to exogenous toxicant exposure,a common insecticide,deltamethrin,and a toxic nectar plant,Bidens pilosa,were chosen as the subjects of this paper.The structural basis of gut microbial response to exogenous toxicant stimuli in A.mellifera was investigated,and the protective effect of honeybee gut microbes on the host was explored by techniques such as pure culture and germ-free bees.The main results were obtained as follows:1.The effect of B.pilosa on worker bee survival,enzyme activity and gut microbes.Worker bees were exposed by different concentrations of B.pilosa extracts.The results showed that ghostwort was orally toxic to worker bees and the toxicity was related to the concentration of ghostwort,the higher the concentration,the stronger the oral toxicity.At 0.02 g/mL B.pilosa exposure,worker bees significantly activated glutathione S-transferase(GST),and when ghostwort concentration was increasing,worker bees also activated carboxyl esterase(CarE)and superoxide dismutase(SOD)activities in turn.In particular,the relative abundance of Bartonella spp.decreased significantly(P<0.001)at all three concentrations.2.Effects of deltamethrin on worker bee survival,diet consumption and gut microbes.Exposure of worker bees by different concentrations of deltamethrin for 48 h.The results showed that the mortality of worker bees was positively correlated with the exposure concentration and exposure time of deltamethrin,while the consumption of worker bee diet was negatively correlated with the exposure concentration and exposure time of deltamethrin.In addition,we performed macrogenomic sequencing of the gut microbes of honey bees exposed to deltamethrin and found that deltamethrin transient exposure significantly altered the structure,flora diversity,and flora function of the honey bee gut microbes.It is noteworthy that 24 h after deltamethrin exposure,compared to 12 h after exposure,the bees also showed significant changes in gut microbes,and there was a tendency for the relative abundance of some core bacteria to revert to that of the control group.3.Protective effect of worker bee gut bacteria on the host after exogenous toxicant exposure.Workers gut bacteria were isolated and cultured,and the protective effect of gut microbes on hosts after worker bee exposure to ghostwort and deltamethrin was explored by aseptic bee technique and fecal transplantation.The results showed that Bartonella apis B2 strain significantly improved host survival after workers exposure to B.pilosa,resulting in 122.67%higher host survival than that of germ-free worker bees exposed to B.pilosa.In addition,different species of gut bacteria isolates of worker bees differed in their protective effects on hosts after host exposure to deltamethrin.Among them,Lactobacillus kunkeei M1 strain showed the strongest host protection with 68.75%host survival,while the next best was Gilliamella apicolaB 1 strain with 66.67%host survival and the worst was Commensalibacter sp.T1 strain with 43.75%host survival.However,the host survival rate of these strains was higher than that of germ-free bees(16.67%).The above results suggest that both B.pilosa and deltamethrin exposure cause honey bee mortality and gut microbial disruption,but that specific gut bacteria increase host resistance to both exogenous toxicants.