Research On The Isolation And Degradation Characteristics Of The Halotolerant Nitrobenzene-Degrading Bacterium

Nitrobenzene (nitrobenzene, shortened form NB) is a kind of important chemicalraw materials and intermediates, which is widely used in the production of aniline, dyes,explosives, plastics, medicine, pesticides and solvents etc. As a result of nitrobenzene withhigh toxicity and refractory biodegradability, much use and emission of nitrobenzenebrings serious threat to the human health and ecological safety. So the study onNitrobenzene degradation is widely concerned by people.It was confirmed that nitrobenzene can be microbial degradation, anddegradation of nitrobenzene on microbial fuel cell research made a preliminaryexploration, but people are more inclined to use traditional microbiological methodsto deal with nitrobenzene wastewater. Aerobic biological method can mineralizenitrobenzene directly, and has became an ideal way to deal with nitrobenzenewastewater, and various nitrobenzene-degrading bacteria have been isolated,including bacteria, actinomyces, white-rot fungus and yeast. In addition, a largenumber of research focus on catabolic pathway and microorganism growth conditionsof nitrobenzene, while fewer study have been carried out under the condition of highsalt nitrobenzene degradation. However, nitrobenzene industrial wastewater oftencontains toxic pollutants such as aniline, phenol, and large amount of inorganic salts.The existence of these substances can make the microbial growth inhibited even losttheir degradation ability. Therefore, screening the strains with high efficiencydegradation for nitrobenzene under hypersaline conditions and reserching its potentialdegradation with the existence of aniline and phenol has the important practicalsignificance.In this paper,22degradation strains utilize nitrobenzene as sole source of carbonunder hypersaline conditions were isolated and screened from activated sludge ofaeration tank in Northeast pharmaceutical factory. Performance study on degradationcharacteristics of22bacteria shows six strains with high degradation ability tonitrobenzene, which are N6, N3, N1, N14, N17and N18. Through the experiment of screening of bacteria, we found out N18is an effective nitrobenzene-degradingbacterium under hypersaline conditions. According to morphological characteristics,physiological and biochemical characteristics and analysis of both whole-cell fattyacid and16S rRNA gene sequence, the bacterium N18is identified as Bacillus cereus.Although there are reports of bacillus cereus spores with the nitro phenoliccompounds as the only carbon source and the growth of the energy, the bacilluscereus spores nitrobenzene degradation was first be reported, so it has the vitalsignificance.The study on growth and degradation characteristics of N18shows that theoptimum inoculation amount for strain nitrobenzene degradation is10%, the optimumtemperature is30℃, the best pH value is7; Under the optimal degradation conditions,when the nitrobenzene concentration is200mg/L, the degradation rate is72.70%in72h.When the salinity is1%-3%, the degradation rate of nitrobenzene is basicallyunchanged, the degradation rate is declined while the salinity increased, but when thesalinity(NaCl) is up to10%, nitrobenzene is also degradable, which is named asmoderate salt tolerant bacteria. Add glucose or sodium acetate as auxiliary carbonsource accelerated the degradation rate raise from72.70%to82.62%and79.25％separately(In72h, when the initial concentration of nitrobenzene was200mg/L);Even150mg/L Phenol or75mg/L aniline mixed into200mg/L nitrobenzene, thedegradation of the strain N18is still effective.the maximum tolerated concentration ofStrain N18to nitrobenzene is400mg/L. It was a good guide for the salt resistancebacteria in the traditional biological treatment and repair system application.Under the1%and3%salinity conditions, the degradation kinetics of N18stainsof nitrobenzene can be expressed by Andrew equation (typical substrate inhibitionmodel).Under1%salinity, the kinetic parameters of strain N18are: μmax=1.61132,Ks=48.5376, Ki=93.39571，R2=0.98138. Under3%salinity, the kinetic parameters ofstrain N18are: μmax=1.47182, Ks=42.67817, Ki=101.28224, R2=0.9814.