Biodegradation Of Aminoglycoside Antibiotics In Sewage And The Fermentation Residue

Aminoglycoside antibiotics,such as kanamycin,streptomycin and gentamicin,have been used so widely for they have many advantages including a wide antimicrobial spectrum,a high bacteriostatic efficacy and a cheap cost.However,taking those antibiotics in large doses for a long time would lead to the emergence of resistant strains inevitably.What's worse,the phenomenon that a lot of fermentation waste was made during the production of antibiotics,which would cause many serious environmental problems and pose clear health danger on human and animals.But don't get pessimistic just yet since some microorganisms can help us remove these dangers in some degree.Previously,three strains were obtained,named Paracoccus kondratievae A1,Paracoccus kondratievae A2 and Aquamicrobium A3,which can degrade the kanamycin,streptomycin and gentamicin amazedly.In addition,the strain A2 was verified that has a strong degrading abilityagainst kanamycin and streptomycin residue.And more important,in order to re-utilizing kanamycin residue,a new solid-state fermentation(SSF)in which several strains were mixed and used as consumers that live on the kanamycin residue mainly was developed.Details are as follows:1.The growing and degrading characterizations of A1(Paracoccus kondratievae),A2(Paracoccus kondratievae)and A3(Aquamicrobium)was Studied.In the mineral salt media,A2 could degrade almost 4000mg/L kanamycin in 64h,while A1 could degrade the same contents of kanamycin in 96h,and A3 could only degrade2000mg/L kanamycin in 104 h.Additionally,using the medium containing 60%LB broth,A2 could degrade more than 90%of 100 mg/Lstreptomycin in 120h.And when it was cultivated in another medium that contained 40%LB broth,it could degrade about 24%of 25mg/L gentamycin in 144h.2.The fermentation culture conditions and medium of strain A2 inkanamycin residue or streptomycin waste was further optimized.Based on single-factor experiment,the optimum culture conditions and medium were determined preliminaryly.Through the Plackett-Burman and Box-Behnken designs,three factors that may be greatly affect the degrading efficiency against kanamycin were screening out,including initial moisture content,inoculating volume and degradation time.Maximum degrading rate of kanamycin residue was obtained when solid state fermentation(SSF)was carried out at the following conditions:theratio of bran and kanamycin residue,2:8;yeast extract,0.1%;the initial moisture content,50%;the volume of sample loading,10g;inoculating volume,40%;temperature of fermentation,34?;degradation time,72h.Under optimum conditions,the degrading rate of kanamycin residue can reach to 89.78%,only 0.59%smaller than that of predicted result.3.The yeast strains(Y.,Y2)which could grow well on kanamycin residue as a single nutrition source was screened from kanamycin residue which has stacked for a long time.According to the NCBI database,ITS sequences comparison analysis and some morphological characteristics,the strain Y1 and Y2 belonged to Candida xylopsoci and Saccharomyces cerevisiae,respectively.Then the strain A2,the both yeasts and one lactobacillus strain(purchased from local market)were used to as complex seed and cultivated it into the medium where kanamycin residue was used as nutrition source.The purposes were to improve the availability of thekanamycin residue,and realize the goals toward not only pollution abatementbut also resource utilization.Through several experiments,the optimal fermentation condition for the complex seedwas ascertained finally.That was:medium,non-autoclaved;total inoculating volume,30%;theratio of inoculum concentration among strain A2,the yeasts and lactobacillus was 2:1:0.5,and it was best to inoculate strain A2 first and cultivate the yeasts and lactobacillus one day after;aerobic and anaerobic cultivation and for 2 days respectively.Cultivated under this circumstance,the kanamycin of fermentation substrate could be reduced to 50.78%,the protein in the fermented liquid could be elevated by 17.58%and excitingly,the substrate smells a little aroma of wine rather than stink.