Optimization of fermentation conditions for production of anti-TMV extracellular ribonuclease by Bacillus cereus using response surface methodology.

Bacillus cereus ZH14 was previously found to produce a new type of antiviral ribonuclease, which was secreted into medium and active against tobacco mosaic virus. In order to enhance the ribonuclease production, in this study the optimization of culture conditions using response surface methodology was done. The fermentation variables including culture temperature, initial pH, inoculum size, sucrose, yeast extract, MgSO(4).7H(2)O, and KNO(3) were considered for selection of significant ones by using the Plackett-Burman design, and four significant variables (sucrose, yeast extract, MgSO(4).7H(2)O, and KNO(3)) were further optimized by a 2(4) factorial central composite design. The optimal combination of the medium constituents for maximum ribonuclease production was determined as 8.50 g/l sucrose, 9.30 g/l yeast extract, 2.00 g/l MgSO(4).7H(2)O, and 0.62 g/l KNO(3). The enzyme activity was increased by 60%. This study will be helpful to the future commercial development of the new bacteria-based antiviral ribonuclease fermentation process.

Purification and some properties of an extracellular ribonuclease with antiviral activity against tobacco mosaic virus from Bacillus cereus.

A new ribonuclease (RNase) with tobacco mosaic virus inhibition was isolated and purified from Bacillus cereus ZH14 through ammonium sulfate precipitation, ultrafiltration, ion-exchange chromatography of DEAE-Sephadex A-50 column, and gel chromatography of Sephacryl S-200HR column. The enzyme was purified approximately 134-fold with a recovery of 9.2%. The RNase had an MW of 75.6 kDa in SDS-PAGE, which differed from RNases reported previously. The inhibitory activity of the RNase in the purification process against tobacco mosaic virus was tested, and the percentage inhibition of the purified RNase (48 U/ml) reached 90%. The protein could tolerate 90 degrees C and pH 4.0.

Isolation and characterization of ZH14 with antiviral activity against Tobacco mosaic virus.

A large number of bacteria were isolated from plant samples and screened for antiviral activity against the Tobacco mosaic virus (TMV). The bacterium ZH14, which was isolated from Chinese Anxi oolong tea, secreted the antiviral substances, having 94.2% virus inhibition when the bacterial culture filtrate and TMV extract were mixed at a ratio of 1:1. The ZH14 strain is a gram-positive, spore-forming rod and has the ability to degrade ribonucleic acid. Based on its effectiveness on virus inhibition, ZH14 was selected for characterization and was identified as a strain of the Bacillus cereus group based on phenotypic tests and comparative analysis of its 16S rDNA sequence. At the same time, we determined the antiviral product of ZH14 as an extracellular protein with high molecular mass, having an optimum temperature of 15-60 degrees C and an optimum pH of 6-10. Hence, the ZH14 strain and its culture filtrate have potential application in controlling plant diseases caused by TMV.