Screening And Identifying Aspergillus Strains Of Higher-yield Lovastatin And Fermentation Conditions Optimizing

Aspergillus is widely distributed in nature,playing an important role in fermentation industry and food processing industry.Aspergillus can produce a variety of enzyme,organic acid,including an important physiological active substances——Lovastatin.Lovastatin has important social value,and has been widely used to prevent cardiovascular disease of humans,its main principle is selective controlling the reductase activity of hydroxymethyl glutaric acid CoA(HMG-CoA),and blocking the biosynthesis of cholesterol.At present,Lovastatin is widely used in food and medicine industry,and has been reported in many fields,such as anti-arrhythmia,diabetes and Alzheimer ’s prevention,anti-infection and rheumatism and anti-tumor.In this paper,Aspergillus strain Ac-32 has been isolated from nature,Through optimizing the conditions of culture medium and fermentation to increase final production.Then completing the test in fermentation based on the result of optimizationFirst,more than 400 strains of Aspergillus have been isolated from the natural world,such as:food,soil,air,organic matter,etc.Then 150 strains Aspergillus were selected via the fungal colony’s characteristics of natural growth and microstructure.Through thin-layer chromatography and the high performance liquid methods selecting a genetic stability and high yield Lovastatin Aspergillus strain which the Lovastatin production reached 75.382 μg/mL.Based on growth status and microscopic features combing with a phylogenetic tree which was established by 18S rDAN sequencing and Blast sequence alignment contrasting,this strain was identified as Aspergillus clavatus,named Ac-32 strain,and subsequent experiments were based on this strain.Second,in order to further improve the production of Lovastatin,we optimi zinged the medium composition and culture conditions,the optimal values of each single factor were:lactose as carbon source,peptone as nitrogen source,carbon content is 100 g/L,nitrogen content is 12 g/L,temperature 28℃,pH 5.2,C/N is 15:1.8,shaking speed is 180 r/min,the age is 4 d,the inoculation quantity is 6%,the Lovastatin production of Ac-32 rose up to 144.021 μg/mL,was 1.91 times higher than original production.On this basis,results of Plackett-Burman design experiments showed that the most significant factors of Lovastatin biosynthesis were temperature,pH,carbon concentration and nitrogen concentration.According to P-B design experiments,through the response surface,establishing the equation:Y=+234.14-7.05A+4.31B-13.41C+11.48D-3.20AB+9.19AC-8.65AD-5.40BC+5.80BD-3.96CD-21.53A2-32.51B2-11.11C2-12.30D2,the optimizing conditions were:nitrogen content is 11.8 g/L,carbon content is 100 g/L,pH 5.2,temperature 28℃ the optimized Lovastatin production reached 224.626 μg/mL.Besides,using the optimal culture medium and fermentation condition,experiments were conducted in 5 L fermentation tank.Through establishing fermentation procession and detecting the production.Growth peaked at 72 h,entering the decline at 120 h;Lovastatin production wasn’t increasing after 108 h and the maximum is 235.02 mg/L.Then extracting Lovastatin from fermented liquid,Lovastatin extractive was 127.07 mg/L,and the extractive rate was 54.07%.Finally,Based on existing laboratory conditions,selecting five kinds of fungi:Fusarium oxysporum,Fusarium graminearum,Alternaria solani,Fusarium solani,penicillium oxalicum and four kinds of bacteria:Escherichia,Staphylococcus aureus,Bacillus subtilis,Xanthomonas oryzae,the antimicrobial activity of Lovastatin was investigated.The results indicated Lovastatin has obviously inhibiting effect to the five kinds of fungi.Compared to the inhibiting effect to fungi,the antibacterial effects of Lovastatin was not obvious except Bacillus subtilis which has obvious inhibition zone.