Browsing by Author "Gamage, S.M.K.W."

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    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 fluorescens
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    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.