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.

Background: We have isolated culture of Streptomyces species that was able to degrade orchid virus capsid proteins and inhibiting virus infection. Odontoglossum ringspot virus infection could be greatly reduced by incubation with the bacterial culture. The infectivity to T4 was reduced after incubation of these culture filtrates, suggesting the activity of the culture filtrate could extend to non-plant viruses. Objectives: To further verify whether the reduction of the infectivity to T4 phage could result in visually measurable difference in the virus morphology after treatment of the bacterial culture. Methods: The T4 phage was grown in DH5-α strain of E coli, and collected in the culture medium. The phage containing medium was filtered with 0.45 μM filter. Two strains of Streptomyces spp, SML-1 and C5-6, were selected based on their optimal growth. The effects of culture filtrate of these two strains on destroying the T4 phage was tested. Morphology of T4 bacteriophage was inspected by atomic force microscopy (AFM). The culture filtrates of SML-1 and CA5-06 strains were diluted to 1/4, and mixed 1:1 to the T4 phage suspension, incubated for 30 minutes, before further 10x and 100x dilution. The mixture was dried on mica and observed using AFM. Results: The culture filtrate of CA5-06 strain is capable of reducing the fragment of the head of T4 phage from an average of 66.5nm to 53.3nm (1/8 dilution). The culture filtrate of SML-1 strain is capable of reducing the fragment of the head of T4 phage from an average of 66.5nm to 62.3nm (1/8 dilution). The data obtained helped to develop practical application methods of the culture filtrates to control virus spreading.