Partial purification and characterization of chiIO8, a novel antifungal chitinase produced by Bacillus cereus IO8.

AIMS: To investigate the distribution of chitinase IO8 in Bacillus cereus strains, the enhancing effects of the chitinase-producing B. cereus strains on biocontrol potential by dual culture assay and in vivo assay against Botrytis cinerea and also the enhancing effects of the chiIO8 on disinfectant properties against seed-borne diseases. Moreover, the application of chiIO8 treatment was also observed to improve the germinative energy. METHODS AND RESULTS: The purification steps included ammonium sulfate precipitation, with columns of DEAE-Sepharose anion-exchange chromatography and Sephacryl S-400 high-resolution gel chromatography. The method gave a 5.8-fold increase in the specific activity and had a yield of 17%. The molecular weight of the partially purified chitinase chiIO8 was found to be around 30 kDa by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). The optimal pH and optimal temperature of the partially purified chitinase were pH 6.5 and 65°C, respectively. The thermostable chitinase still retained the activity after incubation for 100 min at 65°C, and it was increased about 1.25 times than that of the control (before heating) when the enzyme solution heated at 65°C for 60 min. The partially purified chitinase chiIO8 displays a wide inhibitory spectrum towards all phytopathogenic fungi tested. chiIO8 also exhibited effective disinfectant properties against seed-borne diseases. CONCLUSION: The present investigation emphasizes the potential of chitinase-producing micro-organism as promising biocontrol agents of fungal plant pathogens with chitinous cell wall. The novel chitinase chiIO8 proved an efficient, environmentally safe and user-friendly solution. SIGNIFICANCE AND IMPACT OF THE STUDY: This is the first investigation devoted exclusively to analyse the distribution of chitinase in B. cereus. It infers that the chitinase produced by B. cereus might play a role in the activity of the biopesticide.

Assessing the performance of a method of simultaneous compression and encryption of multiple images and its resistance against various attacks.

We introduce a double optimization procedure for spectrally multiplexing multiple images. This technique is adapted from a recently proposed optical setup implementing the discrete cosine transformation (DCT). The new analysis technique is a combination of spectral fusion based on the properties of DCT, specific spectral filtering, and quantization of the remaining encoded frequencies using an optimal number of bits. Spectrally multiplexing multiple images defines a first level of encryption. A second level of encryption based on a real key image is used to reinforce encryption. A set of numerical simulations and a comparison with the well known JPEG (Joint Photographic Experts Group) image compression standard have been carried out to demonstrate the improved performances of this method. The focus here will differ from the method of simultaneous fusion, compression, and encryption of multiple images (SFCE) [Opt. Express 19, 24023 (2011)] in the following ways. Firstly, we shall be concerned with optimizing the compression rate by adapting the size of the spectral block to each target image and decreasing the number of bits required to encode each block. This size adaptation is achieved by means of the root-mean-square (RMS) time-frequency criterion. We found that this size adaptation provides a good tradeoff between bandwidth of spectral plane and number of reconstructed output images. Secondly, the encryption rate is improved by using a real biometric key and randomly changing the rotation angle of each block before spectral fusion. By using a real-valued key image we have been able to increase the compression rate of 50% over the original SFCE method. We provide numerical examples of the effects for size, rotation, and shifting of DCT-blocks which play noteworthy roles in the optimization of the bandwidth of the spectral plane. Inspection of the results for different types of attack demonstrates the robustness of our procedure.

Simultaneous fusion, compression, and encryption of multiple images.

We report a new spectral multiple image fusion analysis based on the discrete cosine transform (DCT) and a specific spectral filtering method. In order to decrease the size of the multiplexed file, we suggest a procedure of compression which is based on an adapted spectral quantization. Each frequency is encoded with an optimized number of bits according its importance and its position in the DC domain. This fusion and compression scheme constitutes a first level of encryption. A supplementary level of encryption is realized by making use of biometric information. We consider several implementations of this analysis by experimenting with sequences of gray scale images. To quantify the performance of our method we calculate the MSE (mean squared error) and the PSNR (peak signal to noise ratio). Our results consistently improve performances compared to the well-known JPEG image compression standard and provide a viable solution for simultaneous compression and encryption of multiple images.