Browsing by Author "Masakorala, K."
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Item Effect of Granite Herbicide on Paddy Soil Microbiota(Uva Wellassa University of Sri Lanka, 2020) Weerasinghe, G.Y. H.; Masakorala, K.; Gunasekara, R.D.A.Granite, which is a systemic herbicide formulation, is widely applied by wet zone paddy farmers in Sri Lanka to control weeds during the initial vegetative growth phase of paddy. The active compound, Penoxsulam; 2-(2,2-difluoroethoxy)-N-(5,8- demethoxy[1,2,4]triazolo[1,5c]pyrimidine-2-yl)-6-trifluoromethyl) benenesulfonamide, destroys both grass and broad leaf weeds through inhibiting Aceto Lactate Synthase (ALS) enzyme. Paddy soil inhabiting microorganisms play a vital role in soil fertility management and suppression of diseases. But, a considerable attention has not been paid to see the effect of Granite on non-target soil microbiota. Thus, the present study evaluated the effect of granite on total microbial activity of rice fields inhabiting microorganisms. After basic soil characterization, 25 g uncontaminated soil was amended with the herbicide Granite to prepare a laboratory contaminated soil series (2.5, 5.0, 10, 15, and 20 ppm of Granite kg-1 of soil). The control consisted with no Granite. All treatments were replicated thrice. Three parallel experiments with 24 (T24h), 48 (T48h) and 168 (T168h) h experimental time were carried out. At the end of each experiment, soil samples were taken from the treatments and soil total microbial activity (TMA) was measured. The highest TMA was measured from the treatment 2.5 ppm of Granite kg-1 of soil and T24h, T48h and T168h exposure times for that treatment were 12.5±0.06, 12.1±0.04 and 10.8±0.34, respectively. The lowest values of TMA recorded from the treatment with the highest contamination level (20.0 ppm of Granite kg-1 of soil ) with T24h, and T168h exposure times of 9.6±0.33, and 8.1±0.20, respectively. Although, the results imply an increasing trend of TMA at acute exposure to lower concentration, the overall results showed a time and concentration dependent irreversible significant (p<0.05), decrease in TMA of treatments with chronic exposure to higher contamination levels of Granite. The overall results infer the potential of negative impact of Granite on rice field inhabiting microbiota due to repeated exposure at high concentrations. Keywords: Granite, Total microbial activity, Herbicide concentration, Exposure, Irreversible effectItem Pseudomonas fluorescens BG-E, a Potential Biological Control Agent for Bloom- forming Cyanobacterial genus, Pseudanabaena(Uva Wellassa University of Sri Lanka, 2021) Wijesooriya, M.M.; Gunawardane, M.H.M.A.S.V.; Randima, G.W.A.P.; Gamage, S.M.K.W.; Masakorala, K.Outbreaks of toxin-producing cynobacterial blooms in freshwater reservoirs in Sri Lanka have increased over the past few decades and are likely to be responsible for fish death reported in many reserviores. Various physical and chemical methods are in practice to eliminate cyanobacterial blooms. However, due to some limitaions adhered with those practices, currently researchers have focused on the applicability of algicidal bacteria as an environmental friendly sustainable control strategy. The present study aimed to investigate cyanolytic and microcystin-LR (MC-LR), degrading potential of heterotrophic bacteria isolated from freshwaters. Sub-surface water samples were collected from Bandagiriya reservoir in Hambantota district. Bacteria were isolated from a composite water sample collected from 22 sampling sites representing the entire reservoir in 50% nutrient agar. Axenic cultures of colonial (Microcystis sp., Synechoccus sp.) and filamentous (Pseudanabaena sp., Pseudanabaena lonchoids, Leptolyngbya, and Geitlerinema sp.) cyanobacterial genera were used as tested cyanobacteria. Seven morphologically distinct bacterial isolates were screened for the lytic activity against cyanobacteria in BG11 broth. Briefly, cyanobacterial cultures at ~ 2×106 cells/mL were inoculated with 10% v/v each bacterial isoates at ~ 1×108 cells/mL. Following 10 days of incubation, distinct discoloration of blue-green into yellowish-brown color in the cell mass of two species of Pseudanabaena was observed in cultures inoculated with BG-E bacterial isolate. Microscopic images provided evidence for complete disintegration of filamentous structures. Disappearance of blue-green color might be due to the oxidation of released photosynthetic pigments during cell wall disintegration. The % lytic activity of BG-E against Pseudanabaena sp. and Pseudanabaena lonchoids based on the chlorophyll-a analysis were 82% and 73% respectively. Bacterial isolate BG-E was identified as Pseudomonas fluorescens by sequencing of its 16S rRNA gene. Since Pseudanabaena is a MC-LR producing and frequently found filamentous form in freshwater reservoirs of Sri Lanka, MC-LR biodegradation potential of BG-E was investigated. Results showed that BG-E is not capable of degrading MC-LR at tested concentrations. Further, none of the genes in the microcystin-degrading gene cluster, mlrABCD were amplified in polymerase chain reaction and might be the reason for the incapability in degrading MC-LR. However, strong cyanolytic activity highlights potential application of P. fluorescens BG-E in future biological control strategies in Sri Lanka. Keywords: Cell lysis; Cyanobacteria; Cyanotoxin; Pseudanabaena; Pseudomonas fluorescensItem Rhizosphere Microbial Activity of Crotalaria retusa L. Grown in Soil Contaminated with Used Lubricating Oil(Uva Wellassa University of Sri Lanka, 2018) Gamage, S.S. W.; Masakorala, K.; Brown, M.T.; Gamage, S.M.K.W.Contamination of soil with used lubricating oil (ULO) has become one of the major environmental issues worldwide. ULO contains highly hazardous chemicals such as phenols, benzenes, heavy metals and polyaromatic hydrocarbons. Therefore, ULO contamination may negatively affect the overall soil quality and biota. Phytoremediation is a green technological approach which uses plants to remove organic and inorganic pollutants from the environment. Rhizosphere microbial activity plays a vital role in the phytoremediation. The aim of the present study is to evaluate the microbial activity in the rhizosphere of Crotalaria retusa L. grown on contaminated soils with ULO. A pot experiment was conducted using contamination levels of 5,000 (T1), 10,000 (T2), 15,000 (T3), 20,000 (T4), 25,000 (T5) and 30,000 (T6) mg kg-1 ULO and uncontaminated control. A randomized block design (RBD) was employed with four replicates per treatment and control. Total microbial activity (TMA) was determined by using fluorescein diacetate hydrolysis (FDA) method and ULO content was determined by using gravimetric method in the soils taken from the rhizosphere in every 30 day interval during 90 days of experimental time. The calculated percentage biodegradation of ULO at the end of the experimental time was 52.2%, 43.8%, 35.6%, 32.2%, 25.2% and 22% for Ti, T2, T3, T4, T5 and T6 ULO treatments, respectively. TMA was 20.22, 18. 05, 16.81, 15.63, 13.94, 11.59 and 10. 59 flourescien 𝜇g ml-1 for unplanted control and T1, T2, T3, T4, 15 and T6 ULO treatments, respectively. According to the results, rhizosphere microbial activity showed a contamination level dependent decrease and a time dependent increase. Further, correlation analysis indicated a highly significant (p < 0.001) positive correlation (r = 0.975) between the percentage biodegradation and the TMA. Therefore, overall results highlight the applicability of the rhizosphere microbial activity as an indicator to assess the biodegradation of ULO.Item Trophic Status and Spatial Variation of Cyanobacterial Diversity in Lunugamwehera Reservoir, Sri Lanka(Uva Wellassa University of Sri Lanka, 2020) Gunawardane, M.H.M.A.S.V.; Gamage, S.M.K. Widana; Wijesooriya, M.M.; Randima, G.W.A.P.; Masakorala, K.; Atapattu, K.S.S.; Sanjaya, K.Lunugamwehera is a large man-made reservoir located in the South Eastern dry zone of Sri Lanka. It is the main source of drinking water, irrigation, and fisheries for more than 5000 families in the area. The occurrence of cyanobacterial blooms or high population densities in water bodies results in various environmental and health issues. Population density and composition of cyanobacteria in a waterbody may vary with the trophic status of water. There is a high potential of contaminating the Lunugamwehera reservoir with mineral nutrients that come from agricultural lands. However, considerable attention has not been paid to study trophic status and cyanobacterial diversity of the Lunugamwehera reservoir. Therefore, our objective was to determine the spatial variation of cyanobacterial diversity in the Lunugamwehera reservoir along with trophic status. Sub-surface water samples collected from 28 sampling sites representing the whole waterbody were microscopically examined to identify cyanobacterial species. Total phosphorous concentration, total chlorophyll-a concentration, and Secchi depth were determined to assess trophic status using Carlson Trophic State Index. Also, water quality parameters were measured using a multiparameter water quality meter. Microscopic analysis revealed the presence of only two cyanobacterial species, Microcystis and Oscillatoria implying less cyanobacterial diversity in the reservoir. Microcystis spp. (~3.257 x 107 cells mL-1 ) dominated all sampling sites with significant difference (p<0.05) in cell densities among sites while Oscillatoria spp. (5 - 10 cells mL-1 ) occurred rarely. Apart from cyanobacteria, Pediastrum spp., Tribonema spp. and Nitzschia spp. (1 - 2 cells mL-1 ) were also identified scarcely. Water quality parameters were approximately similar in all sampling sites except increased turbidity near the inlet. According to the Carlson Trophic State Index (37.70), the water body was ‘slightly oligotrophic’. Therefore, the overall results infer the presence of less cyanobacterial diversity and significant spatial variation in Microcystis spp. as the dominant species in the slightly oligotrophic water of the Lunugamwehera reservoir. Keywords: Carlson trophic state index, Cyanobacteria, Oligotrophic, Spatial variation