Browsing by Author "Gunawardane, M.M."

Now showing 1 - 6 of 6

Chromium accumulation in Cr (VI) resistant bacteria
(Book of Abstracts, Annual Research Symposium 2014, 2014) Abewickrama, J.H.G.; Jayarathne, D.L.; Rathnayake, I.V.N.; Gunawardane, M.M.
Accumulation of Cr(VI) is one of the methods used in bacteria to overcome elevated chromium concentrations. These hyperaccumulators of Cr(VI) are important in bioremediation of Cr (VI) containing wastes. Accumulation of Cr(VI) has been previously reported in Alcaligenes eutrophus CH34, Bacillus subtilis and some Pseudomonas sp. During this study Chromium accumulation of a Cr (VI) resistant Psuedomonas sp., Escherichia coli JM109 and the transformant E.coli JM109 with plasmids extracted from the Cr(VI) resistant Pseudomonas sp. were compared. Cr (VI) accumulation was estimated at 0, 5, 10, 15 mg/L Cr (VI) concentrations after 72 hour exposure time. The cells were subjected to acid lysis and the chromium concentrations were estimated using Atomic Absorption Spectrometry. Cr (VI) accumulation percentages of Cr (VI) resistant Pseudomonas sp. under 5, 10, 15 mg/L Cr (VI) concentrations were 51.38%, 37.46% and 43.13% respectively. Those percentages were 2.6%, 1.54%, and 1.12% for E.coli JM109 while they were 35.58%, 20.06% and 34.03% for the transformant. There is a possibility of chromium accumulation being regulated by Cr (VI) resistant genetic determinants found on plasmids. In addition, the nature of the host that bears the plasmid is also important for the Cr (VI) accumulation mechanism.These hyperaccumulators of Cr (VI) showed potential use in bioremediation of Cr(VI) containing wastes.
Construction of biosensors using lux operon
(Faculty of Science, University of Kelaniya, Sri Lanka, 2016) Munasinghe, D.T.P.; Gunawardane, M.M.
The lux operon is the cluster of genes that encode luminescence in light emitting bacteria. Expression of this operon or parts of it can be utilized in the construction of biosensors, which are genetically modified organisms, often bacteria that can be used to detect and measure environmental chemical factors such as pollutants. This type of biosensors is constructed in such a way that light emission occurs due an environmental signal ‘sensed’ by a ‘sensor gene element’. The sensor element acts as a promoter that triggers on the expression of a reporter gene element, for example lux genes, fixed immediately downstream to it. The intensity of the light emission can be measured using a luminometer and it gives not only a quantitative measurement of the environmental factor but also an indication of the bioavailability of the factor. The lux operon is consisted of seven genes, i.e. luxR, I and CDABE. Each of the genes is responsible for a specific function. The luxR and luxI products act as the auto inducer for the gene expression, which are not needed in a biosensor because there is the sensor element to act as the promoter. The plasmid pSB2025 constructed previously by another research group and which contains sections of the lux operon modified for the expression in both Gram negative and positive bacteria, provides a promoter-less gene sequence that can be used in the construction of biosensors with a suitable promoter of choice. Promoters of genes of various bacteria that are expressed upon exposure to heavy metals or DNA damaging factors, would be ideal sensor elements in the construction of biosensors that can be used to detect and monitor environmental pollution caused by such factors. Such biosensors would provide a tool cheaper than chemical analysis of pollutants.
Isolation and characterization of Rhodomicrobium vannielii from Winogradsky column
(Sri Lanka Association for the Advancement of Science, 2015) Weerasingha, P.D.S.; Gunawardane, M.M.
Isolation and identification of Thiobacillus species and cellulose degrading Clostridium species from Winogradsky column
(Sri Lanka Association for the Advancement of Science, 2014) Weerasingha, P.D.S.; Gunawardane, M.M.
Photosynthesis: Synthesis of what?
(Faculty of Science, University of Kelaniya, Sri Lanka, 2016) Gunawardane, M.M.
The term photosynthesis is often used to mean the entire chain of biochemical reactions, which is initiated by light and concluded by the synthesis of carbohydrates. This series of reactions has two clearly distinct stages. First, there is the synthesis of ATP and reduced coenzymes (e.g. NADPH) with the help of light energy. Next, ATP and a reduced coenzyme are used in the synthesis of carbohydrates (e.g. starch) from CO2. As the first stage involves light, it is known as the light reaction of photosynthesis, while the second stage, which does not require light, is known as the dark reaction of photosynthesis. The dark reaction in nature is not a process necessarily dependent on a photomediated activity, the light reaction. What dark reaction needs for the reduction of CO2 into organic carbon is a reduced coenzyme and ATP, and the source of those compounds does not necessarily have to be the light reaction. This review proposes that the dark reaction should not be described as part of photosynthesis. Dark reaction is not a process limited to organisms that use photo energy to produce ATP and reduced coenzymes. In fact, without any dependence on photo energy, it happens in nature in some non-photosynthetic chemotrophic organisms as well. Thus, the light reaction is not an essential precondition for the dark reaction. Furthermore, ATP and reduced coenzymes synthesized by the light reaction in nature are not entirely used for the dark reaction. As such, the light reaction is not an activity that leads only to the dark reaction. Since the dark reaction can occur independently from any photo-driven synthesis process, it should not be described as part of photosynthesis. Therefore, the term photosynthesis should be confined to describe only the light reaction, defining photosynthesis as the process in nature that synthesizes ATP and reduced coenzymes using light energy. Dark reaction, which describes fixation of CO2 in to organic compounds, is an activity carried out by photosynthetic organisms and certain chemolithotrophic bacteria as well. It can be appropriately described by the term autotrophy, defining it as the primary production of carbohydrates in the biosphere.
Plasmid mediated Chromium resistance of bacteria
(Book of Abstracts, Annual Research Symposium 2014, 2014) Abewickrama, J.H.G.; Jayarathne, D.L.; Rathnayake, I.V.N.; Gunawardane, M.M.
Plasmid-mediated Cr(VI) resistant bacteria are naturally found in environments contaminated with chromium releasing industrial effluents. These envirnments may contain microorganisms those have genetically regulated mechanisms to overcome elevated Cr(VI) levels. Such mechanisms could be regulated by genes found either in chromosomal DNA or plasmid DNA. In order to understand the exact mechanism and for the possible use of such mechanisms in monitoring and control of heavy metal pollution, it is important to determine whether the resistance is plasmid borne or controlled by chromosomal DNA. There are certain plasmids which contain genes to resist highly toxic hexavalent chromium (chromates and dichromates). Resistance to chromate is determined by decreased chromate transport by the resistant cells. The genes for a hydrophobic polypeptide, ChrA, have been identified in Cr(VI) resistance plasmids of Pseudomonas aeruginosa and Alcaligenes eutrophus.