Browsing by Author "Samarasinghe, D.G.S.N."

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Diversity of Firmicutes in selected hot water springs of Sri Lanka by 16S metagenomic sequencing
(Faculty of Science, University of Kelaniya, Sri Lanka, 2020) Samarasinghe, D.G.S.N.; Wanigatunge, R.P.; Magana-Arachchi, D.N.
Thermophiles have the ability to survive in environments with very high temperatures. Hot springs provide unique natural environments for these thermophilic microorganisms. In recent years, hot water springs and thermophilic microorganisms have gained attention due to their industrial and biotechnological importance. Among the thermophilic bacteria, a large number of metabolites can be found in the phylum Firmicutes. Different species of Firmicutes show various ecological optima. Even though Sri Lanka harbors many hot springs, majority of them are not yet explored and require comprehensive studies to unravel the inhabitant microbial diversity, specially the phylum Firmicutes. This study was focused into uncovering the resident thermophilic Firmicutes which could be unculturable and their diversity in four major hot springs namely, Mahapelessa, Wahawa, Maha Oya and Nelumwewa using 16S rRNA metagenomic sequencing. Water samples were collected from the four hot springs in which the surface temperature ranged from 44.2 to 53.8 °C. Further, a water sample from a natural spring located in Digana (26.9 °C) was used as the control. Genomic DNA was extracted from the water samples using modified Boom’s method and was subjected to 16S rRNA metagenomic sequencing (16S V3-V4 region) using Illumina platform. The results were analyzed using GAIA: Metagenomics data analysis software to identify Firmicute bacteria (Operational taxonomic units/ OTU) and to determine their relative abundance. OTU analysis was carried out with a cut-off similarity value at 97%. The relative abundance of Firmicutes in each spring is as follows: Mahapelessa (23.7%), Wahawa (0.8%), Maha Oya (0.9%), Nelumwewa (5.8%) and Digana natural spring (4.2%). The class Clostridia and Bacilli were the most abundant classes observed in hot springs. A total of twenty-one species were affiliated with the phylum Firmicutes, among which 18 species were only detected in hot water springs while the rest of the three species (Clostridium sp., Flintibacter butyricus and Oscillibacter sp.) were only detected in the natural spring. Nine different bacterial species were unique to Mahapelessa hot spring including; Bacillus licheniformis and Bacillus thuringiensis belonging to class Bacilli, Caldanaerocella colombiensis, Desulfotomaculum reducens, Geosporobacter sp., Geosporobacter subterraneus, Pelotomaculum isophthalicicum, Salimesophilobacter vulgaris and Tepidibacter sp. belonging to the class Clostridia. The two bacterial species; Carboxydocella manganica and Faecalibacterium prausnitzii were only recorded from Maha Oya while Clostridium islandicum was reported from Maha Oya and Nelumwewa hot springs. Bacillus pumilus and Sporacetigenium mesophilum were present in Mahapelessa and Wahawa hot springs. Anaerosolibacter carboniphilus was found in both Mahapelessa and Nelumwewa while Anaerobacterium chartisolvens was detected in all hot water springs except Wahawa. Bacillus sp. and Paenibacillus sp. were common in all the hot water springs. When compared to the natural spring, the four hot water springs showed high bacterial species diversity (85%). Results from this study confirm the uniqueness of bacterial species belonging to phylum Firmicutes in hot water springs than in the natural springs. More comprehensive studies on these Firmucutes are needed to identify their potential to be used in industrial and biotechnological applications.
Isolation and identification of thermophilic bacteria and cyanobacteria from Maha Oya hot springs in Sri Lanka
(Research Symposium on Pure and Applied Sciences, 2018 Faculty of Science, University of Kelaniya, Sri Lanka, 2018) Medhavi, P.I.H.R.; Samarasinghe, D.G.S.N.; Herath, H.
Hot springs are a rich source of thermophilic microorganisms such as bacteria, cyanobacteria and archaea. Though, there are several hot springs recorded in Sri Lanka, a comprehensive community analysis of thermophilic microorganisms in these springs is inadequate. Therefore, the present study was conducted to isolate and identify the thermophilic bacterial and cyanobacterial diversity in Maha Oya hot springs. Water samples were collected from the surface and the bottom of the seven wells of Maha Oya hot water springs, which showed temperatures ranging from 42 to 59.80C and pH ranging from 6.89-7.63. Water samples treated with Lugol’s iodine as well as microbial mats growing on water surface and attached to the surface of wells, were observed under a light microscope to determine the presence of cyanobacteria. Thermophilic bacteria were isolated by inoculating a dilution series (100, 10-2 and 10-4) of water samples separately into nutrient agar medium and incubating at 550C for 48 hours. Water and microbial mat samples were inoculated into cyano-specific BG11 and BG110 media and incubated at 550C and 12:12 hours dark:light cycle to isolate culturable thermophilic cyanobacteria. Based on morphological (colony morphology, Gram staining, endospore staining and motility test) and biochemical (oxidase activity, catalase activity, H2S production, citrate utilization, glucose fermentation) characteristics, the isolated bacteria were identified as Bacillus thermoamylovorans, Meiothermus sp. and Bacillus schlegelii which have been previously reported as thermophiles. Morphological identification of both uncultured and cultured cyanobacteria revealed the presence of eight different cyanobacterial genera. The most abundant genus was Oscillatoria . Additionally, Calothrix, Synechococcus, Gloeocapsa, Gloeothece, Cylindrospermopsis, Lyngbya and Pseudanabaena were observed. The isolation and identification of these thermophiles could be useful in mass scale production of thermostable enzymes and other bioactive compounds with biotechnological and industrial applications.
A preliminary floristic study of Chundikulam forest reserve in Jaffna peninsula
(Faculty of Science, University of Kelaniya, Sri Lanka, 2016) Ekanayake, G.C.M.; Medhavi, P.I.H.R.; Somasiri, R.P.I.V.; Jayalath, W.G.H.; Siriwardhana, K.H.W.; Samarasinghe, D.G.S.N.; Kannangara, S.
Chundikulam sanctuary is a reserve which is located in the Northern Province, in Jaffna peninsula. This reserve is situated in the dry zone of Sri Lanka and the area consists of mangroves along the shores and scrub lands in the sandy areas. The Jaffna peninsula, including Chundikulam, faced an ecological destruction due to the Sri Lankan civil war which prevailed for almost three decades. Therefore, due to the paucity of data of this arid vegetation, this current study was carried out as the first investigation after war. According to the surveys, Chundikulam covers an area of 19,000 hectares in vegetation. A systematic study on the vegetation of this dry arid zone forest was carried out using randomly selected representative sampling sites to document the vegetative diversity of the region, through a field survey conducted in the peripheral areas of this reserve in March 2016. Five quadrates (10m×10m) per site were placed totaling to 25 random sample collections. Eighteen different plant species were collected during the study and herbarium specimens were prepared and submitted to the Department of Botany herbarium, University of Kelaniya, Sri Lanka. The plant species sampled were trees (8 species), shrubs (4 species) and creepers (6 Species). Among them Carissa spinarum, Borassus flabellifer, Drypetes sepiaria, Stereosperum colais, Prosopis juliflora. Dillenia sp., Pterocarpus sp. were tree species and Atalantia ceylanica,and Memwcylon umbellatum were recorded as shrubs and Euphorbia antiquorum, Jasminum officinale, Hardenbergia sp. were identified as creepers. The dominant plant species of the vegetation was Drypetes sepiaria (Putranjivaceae) while Borassus flabellifer (Arecaceae) was the most abundant.The total vegetation cover was estimated by the mean number of individuals (30.4%). The plant communities that have been recognized in this study within the arid and dry forest in Chundikulam forest reserve will provide preliminary scientific data for a systematic review of the changes in their vegetation after the war which prevailed for almost three decades.