Microbiology

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Author: search.filters.author.Jayaratne, D.L.

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    A preliminary study on application of phage-indicator model in evaluation of antiviral drugs
    (Sri Lanka Association for the Advancement of Science, 2015) Malalasekara, A.M.A.L.R.; Jayaratne, D.L.
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    Ratoon stunting disease of sugarcane in Sri Lanka
    (Natural Resources, Energy and Science Authority of Sri Lanka, 1987) Jayaratne, D.L.; Widanapathirana, S.
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    Effective biocide options for eliminating Ceratocystis spp associated with coir products
    (Sri Lanka Association for the Advancement of Science, 2011) Senavirathna, H.G.L.A.K.; Jayaratne, D.L.
    This study describes the determination of suitable methods for eliminating the fungus Ceratocystis associated with coir products. Ceratocystis spp is a pathogen causing diseases in several plants including coconut. The occurrence of this organism in coconut cultivations in Sri Lanka has been reported since 1906. Sri Lanka has extensive coconut cultivation and many coir products are exported. It is a quarantine requirement that the coir products are free from this organism. Currently, methyl bromide is used as a fumigant to eliminate the organism, but the use of this chemical is restricted due to its high toxicity and because it affects the ozone layer. In this study the organism was isolated from the coir dust samples collected from the areas of Lunuwila and Kurunegala. The morphological characters of spores were similar in the isolates obtained from these two different locations. However, the color of the chlamydospores was darker in the isolates obtained from Kurunegala than in the samples collected from Lunuwila. The effectiveness of the fumigant formaldehyde (37% formaldehyde 120 ml with 60 g potassium permanganate for 2.83 m3 or 100 ft3 air space) was tested in fumigation chambers parallel with methyl bromide (48 g/m3) on a Potato Dextrose Agar culture and in inoculated coir dust. The formaldehyde was effective for inoculated coir dust but not for the fungus grown on culture plates, while methyl bromide was effective for both. As an alternative method, water vapor heat treatment was applied at different time temperature combinations on coir dust inoculated with fungal spores. At 55 °C for 5 min., the vapor heat treatment destroyed the viable spores in it. For the elimination of Ceratocystis associated with coir dust, formaldehyde can be used in place of the currently used methyl bromide. Formaldehyde is less effective when the organism is grown on culture media due to the different conditions prevalent in culture media and coir dust. Besides the chemical formaldehyde, heat treatment can be applied for eliminating the organism. A temperature of 55 °C generated from water vapor for 5 minutes is sufficient for eliminating the fungal spores.
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    Microbiological investigations of Sigiriya Frescos
    (2006) Fernando, S.; Jayaratne, D.L.
    The archaeologically valued Frescoes at Sigiriya, a World Heritage Site in Sri Lanka,play a major role in remarkable historic interest. Microbial growth on fresco paintings has been identified worldwide as a significant factor which affects the quality of paintings. Microbiological investigation of fresco paintings therefore has become an important aspect of conservation strategy. The microbiological investigation of the Sigiriya frescoes was carried out in June 2005 by visual detection, microscopic investigations and using microbial culture techniques. The samples for microbial culture techniques were taken from each colour regions separately using sterile cotton swabs and cultured in Nutrient Agar (NA), Trypton Soy Agar (TSA) and Potato Dextrose Agar (PDA) media.The observations revealed that the fresco surface was free from any fungal, lichen or cyanobacterial growth but eleven bacterial cultures were isolated from a decayed patch,from non painted plaster and from a cavity. All the isolates belong to the Genus Bacillus having no conformity with any of the Bacillus spp either indicated in ?Bergy?s manual of systematic bacteriology vol I and II or included in the computer database developed by Trevor Bryant, University of Southampton, UK (2005). One isolate showed similar morphological characteristic features to the Bacillus decoloratiois sp. Nov. bacterium which has been proposed for the new isolate that was responsible for de-colorization of the fresco paintings in Spain and Austria. However, the biochemical characterization of the isolate showed that is a distinctive species having no conformity with Bacillus decoloratiois sp. Nov. Further characterizations using DNA based techniques are being carried out in order to determine whether the isolate is a new species or a similar strain of the Bacillus decoloratiois sp. Nov. In the process of conservation, periodic monitoring and further investigations are being carried out for the detection of microbial growth forms including the Bacillus species on the fresco paintings in order to protect them from any microbial de-colorization and degradation.