Effects Of Aspergillus Niger Indirect Bioleaching On Heavy Metals,Antibiotics And Antibiotic Resistant Genes In Chicken Manure

Livestock manure,rich in organic matter and nutrients,is a kind of traditional organic fertilizer,but presently,it contains excessive amounts of heavy metals and antibiotics,so if being applied directly to farmland,it may create accumulations of heavy metals,antibiotics,and the residues of antibiotics in the environment can induce the emergence of antibiotic resistant genes(ARGs).Besides,these pollutants not only affect the growth of crops,but even cause harm to human health and lead to serious public health problems,so it is necessary to conduct harmless treatments for livestock manure.Though the traditional methods like compost can effectively kill the pathogenic bacteria and degrade antibiotics in the manure,it cannot reduce or stabilize heavy metals.Moreover,bioleaching technology was first applied to extract useful metals from ore.Due to its advantages including low operation cost,wide application,simple operation and low pollution level,it was later applied to remove heavy metals from pollutants.Aspergillus niger,a kind of commonly used bioleaching microorganisms,secreting organic acids during the growth and metabolism process,can dissolve metals.At present,biological leaching of Aspergillus niger is mainly used in municipal waste incineration fly ash,red mud and other materials,but there are few reports on the removal of heavy metals in livestock manure,and the effect on antibiotics and ARGs has not been studied.As a result,in order to study the effect of bioleaching technology on harmless treatment of livestock manure,this paper employed Aspergillus niger bioleaching technology to remove heavy metals from chicken manure,as well as the changes of heavy metal morphology,degradation rate of antibiotics and changes of ARGs during the leaching process.This work provide a new idea for the treatment of livestock manure.In this paper,the fungus with excellent organic acid production ability was first isolated and purified from the chicken manure,rooting in a chicken farm in panyu district,guangzhou city.By morphological analysis and 18 S rDNA sequence identification,it was identified as Aspergillus niger,and the registered serial number was MH978907.On the other hand,the yield of citric acid was much higher than that of other organic acids,whose concentration reached 86.46 mmol/L after 25 days culturing.Subsequently,the orthogonal experiment to optimize the production of citric acid was conducted to get the optimized condition(120 g/L medium concentration,40 mL/L inoculation amount,30 ℃ culture temperature,the citric acid concentration reached 94.20 L after 15 days culturing.Aspergillus niger fermentation with rich citric acid was cultured under optimized conditions for leaching heavy metals(Cu,Zn,As)in chicken manure,and morphological changes of heavy metals during the leaching process were studied.The results showed that indirect leaching of Aspergillus niger had a good effect on removing heavy metals from chicken manure.Besides,the removal rates of Cu,Zn and As were 63.93%,79.22% and 42.55%,respectively,whereas concentrations of heavy metals reached the standard of Soil Environmental Quality Farmland Soil Pollution Risk Control Standard(Trial)(GB15618-2018).After leaching,the morphology of heavy metals changed greatly and the bioavailability decreased greatly.For Cu and Zn,the larger the proportion of heavy metal morphology was,the greater the reduction after leaching became,while the residual was more stable and difficult to leach.Afterwards,the degradation of antibiotics in chicken manure and the change of ARGs were investigated.The results revealed that bioleaching had a certain effect on degradation of antibiotics.Several antibiotics like norfloxacin,ciprofloxacin,enrofloxacin and oxytetracycline degraded by 28.23%,68.92%,68.24% and 33.28%,respectively,however,the relative abundance of 8 ARGs was lower than the initial value.Moreover,the relative abundance of the three quinolone resistance genes increased slightly in the later stage,but was still lower than the initial value.PERMANOVA(Permutational multivariate analysis of variance)analysis showed that the ARGs and carbon and nitrogen ratio(C/N)had a negative correlation,and heavy metals(Cu,Zn,As),antibiotics(NOR,CIP,ENR,OT),organic matter(OM)were positively correlated.Among them,sul2,tetO and tetC were associated with all physical and chemical factors(p<0.05),indicating that these genes may exist in the same chromosome or the same host bacteria.