Screening Of The Salt-tolerant Strains With High Protein-degradable Ability And Optimizing The Parameters Of Complex Microbial Preparation

High protein content sewage, especially high salt content, is a headache problem forenvironment controlling. If discharged it directly, it is always to pollute the river for its highorganic content. Therefore, in order to screen some special strains for degrading the residualproteins in sewage under the high salt content conditions, the sample were collected nearbythree dining halls in Lanzhou Jiaotong University.4strains were screened from these sampleswith high degradable ability for protein under salty content. After indentified by biochemicaland16S rDNA technology ways, and optimized the different fermented con parameters, aswell as researching the different ratios of complicated stains for degradation, the results werelist as follow:(1) Four halophilous protein degradation stains were isolated from restaurant wastewaterby salt tolerance test and fermentation test, named A-3, D-3, F-2and K-1. they have super salttolerance (2%) and degradable ability for protein. Research showed, under20℃, that thedegradation rate of these four strains were75.31%(A-3),70.47%(D-3),64.14%(F-2)and68.82%(K-1).(2) Based on morphologic observation, biochemical characteristic and identification of16SrDNA, A-3and F-2belongs to the genus of Serratia, D-3belongs to the genus of Bacillus,K-1belongs to the genus of Acinetobacter. Registered their16S rDNA sequence in theGenBank and get the accession numbers are A-3: KF864660, D-3: KF864663, F-2:KF864662, K-1: KF864661.(3) Based on the different growth conditions, such as different pH, different saltconcentration and different cations, different growth characters were tested as followed. Asthe concentration increased, the lag phase of growth gradually extended, along with thegeneration time gradually growing. The optimum pH for A-3growth was7.0, K+and Mg2+promote the strains growing, Ca2+were inhibit its growth; The optimum pH for D-3growthwas7.0, Mg2+has little effect on the growth of the strain, K+and Ca2+were inhibits thestrain’s growth; The optimum pH of F-2was6.0, K+and Ca2+inhibits the growth of strainand Mg2+has little effect on its growth; and the optimum pH for K-1growth was6.5. Themedium of Mg2+and K+were nothing to do with K-1, however Ca2+could inhibits the growthof strain.(4) Four influencing factors such as initial pH, dissolved oxygen, inoculum size andcarbon source were selected to do degradation inoculation experiments, and optimized byorthogonal experimental design. Meanwhile, the optimal composition of the fermentationmedium and the component ratio were made sure. The results showed that: ○1The optimum degradation conditions of strain A-3was pH7.0, dissolved oxygen180r/min,5%inoculum concentration. The sucrose can promote the protein degradation ofA-3. The optimum conditions of medium for formentation listed as follows: Casein10g/L,sucrose5g/L, yeast extract2g/L, K2HPO43g/L, With the optimum conditions, the proteindegradation rate improve form75.31%to82.07%.○2The optimum degradation conditions of strain D-3was pH7.0, dissolved oxygen180r/min,4%inoculum concentration. The sucrose can promote the protein degradation ofD-3. The optimum conditions of medium for formentation listed as follows: Casein15g/L,sucrose5g/L, yeast extract3g/L, K2HPO42g/L, With the optimum conditions, the proteindegradation rate improve form70.47%to79.63%.○3The optimum degradation conditions of strain F-2was pH6.0, dissolved oxygen210r/min,4%inoculum concentration. The sucrose can promote the protein degradation ofD-3. The optimum conditions of medium for formentation listed as follows: Casein15g/L,sucrose15g/L, yeast extract2g/L, K2HPO41g/L, With the optimum conditions, the proteindegradation rate improve form64.14%to76.96%.○4The optimum degradation conditions of strain K-1was pH6.0, dissolved oxygen210r/min,3%inoculum concentration. The sucrose can promote the protein degradation ofK-1. The optimum conditions of medium for formentation listed as follows: Casein5g/L,sucrose10g/L, yeast extract2g/L, K2HPO42g/L, With the optimum conditions, the proteindegradation rate improve form68.82%to80.45%.(5) The optimal ratios of different strains and fermented conditions were determined byorthogonal experiment method. The study show that:when the strain A-3:D-3:F-2=3:2:4with3%of the total inoculum, the rate of protein degradation is the highest. The best fermentedconditions were listed as fllow: At pH6.0, sucrose as a carbon source, yeast extract asnitrogen source, dissolved oxygen as180r/min, the maximum degradation rate of thecomposite strain, was92.37%.