No abstract

Introduction: Streptomyces species culture was isolated and identified. Its filtrate was found to be able to damage Odontoglossum ringspot virus and Cymbidium mosaic virus coat protein in our previous study. It is absolutely necessary to establish its biohazard level and toxicological profile before this filtrate or its active compound can be used for immediate disinfection of the equipment and bench surface, or even technician’s skin. Aim: In this study we intend to test the mutagenicity of this culture filtrate using the mouse lymphoma assay (MLA). Material and methods: Streptomyces species was cultured for 14 days, and the medium was collected for XTT assay to determine the highest concentration of the culture filtrate that do not cause reduction in cell number. In vitro mammalian cell gene mutation test using Mouse lymphoma L5178Y TK+/- was used to evaluate the mutagenic potential of the culture filtrate in accordance with OECD (1997), test No. 476: in vitro Mammalian Cell Gene Mutation Test. Result: Our cytotoxicity assay revealed that 1.33% of the culture filtrate was the maximal concentration that would not inflict reduction in cell number. The result of mutation test showed that with 3-hour treatment and S9 metabolic activation, the culture filtrate did not show significant mutagenicity when compared to the negative controls (ANOVA and Student t-test, p<0.05). Summary: This data suggested that the culture filtrate is not mutagenic.

A Streptomyces spp. culture was isolated and identified. Its filtrate was found to be able to destroy ORSV and CYmMV virus coat protein, and could be used to reduce the transmission of plant virus disease in vivo, in our previous study. We also tested and found that it can destroy the coat proteins of 13 other of plant viruses, suggesting that the mechanism of action is not specific to a few plant viruses. Aim: To test if this culture filtrate can destroy or affect the infectivity of non-plant viruses. Materials and methods: Streptomyces spp. were cultured in soybean-based culture medium for 14 days, and the culture was collected and filtered. T4 phage infection of E. coli was used as a model. E. coli was cultured on 0.75% TSA agar plates. The T4 phage was incubated with various concentrations of Streptomyces spp culture filtrate for 30 minutes, before adding to the E. coli lawn. Culture filtrates of two strains, the C5-6 and the SML-1, were used. T4 phage incubated with 300 ppm virusbom (a known anti-viral agent) was used as a positive control. The formation of T4 lysis colony was calculated for the plaque-forming unit (PFU). Results: The dilution of 1 in 8 of the culture filtrates reduced the number of phage colony on E. coli lawn. The infectivity was significantly reduced when T4 was incubated with the culture filtrate at 1/8 dilution when compared to the non-treated groups. The virusbom treated PFU was significantly reduced, in comparison with C5-6 treated group (P=0.013), and with SML-1 treated group (P=0.028) as per ANOVA test followed by Tukey post-hoc comparison. Summary: These data demonstrated that culture filtrates of Streptomyces spp. reduced T4 to E. coli infectivity and suggested that the anti-viral compounds in the filtrate is not specific to plant viruses. The application of the culture filtrate and its content might have broader applications.