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Articles by R. Thavasi
Total Records ( 5 ) for R. Thavasi
  R. Thavasi , S. Jayalakshmi , R. Radhakrishnan and T. Balasubramanian
  The present investigation is on evaluation of biodegradation potential of four species of hydrocarbonoclastic bacteria, B. megaterium, C. kutscheri, L. delbrueckii and P. aeruginosa and screening for plasmids. For biodegradation study, the strains were cultured in mineral salt medium with 0.1% of crude oil for seven days. Biodegradation results inferred that, P. aeruginosa showed 85.15% of crude oil degradation, followed by B. megaterium (78.5%), C. kutscheri (76.4%) and L. delbrueckii (71.6%). Strains were grown for 24 h in Luria-Bertani broth for plasmid study. Plasmid study revealed that, P. aeruginosa harbored two plasmids with molecular weight of 4.2 and 3.8 kb. The other strains namely L. delbrueckii, C. kutscheri and B. megaterium were found to have single plasmid with respective molecular weight of 3.8, 4.2 and 4.1 kb. Complete loss of biodegradation potential was observed when the plasmids of these strains cured with acridine orange.
  M. Rajkumar , R. Thavasi , P. Perumal and Jean-Paul Trilles
  The attempt of the present study is to achieve an approach of the magnitude of parasite induced secondary infection estimation of Vibrio, Salmonella and Pseudomonas loads as well as the total heterotrophic bacteria using a battery of biochemical tests. The parasitic isopod Nerocila phaiopleura was collected from commonly available fish Stolephorus commersonii at Parangipettai, India. Parasites settled on the branchial and external body surface of the fish causes red coloured skin lesions, where secondary bacterial infections were detected. THB and Vibrio counts were higher in the infected hosts than in the healthy fish and it was found to 7.2x105 and 3.5x103 cfu g-1 in branchial regions and 5.4x105 and 2.3x103 cfu g-1 in the body surfaces, respectively. Salmonella counts were found as 6.0x103 and 3.6x101 cfu g-1 in branchial regions of the infected and uninfected fish and in body regions, 3.9x103 and 1.03x102 cfu g-1, respectively. Pseudomonas counts were 7.0x102, 4.9x101 cfu g-1 in branchial regions and 6.2x102, 5.8x101 cfu g-1 in the body surfaces of the infected and uninfected fish. Statistical analysis of the results (t-test) showed high significant value (p<0.05).
  N. Annamalai , R. Anburaj , S. Jayalakshmi and R. Thavasi
  In the present study water, ethanol, methanol, acetone, hexane and butanol extracts of two Bivalves, Perna viridis and Crassostrea madrasensis were screened for antibacterial activity. The extracts were obtained from whole body tissue of the animals and tested against 10 different pathogenic bacteria viz., Escherichia coli, Klebsiella oxytoca, K. pneumoniae, Lactobacillus vulgaris, Proteus mirabilis, Pseudomonas aeruginosa, Salmonella typhi, S. paratyphi, Staphylococcus aureus and Vibrio sp. Ethanol extract of P. viridis showed maximum antibacterial activity against E. coli and S. aureus. Ethanol extract of C. madrasensis exhibited highest activity against S. aureus. Water extract of P. viridis and C. madrasensis showed highest activity against E. coli and P. mirabilis, respectively. The 10:10 (methanol: ethanol) fractionated extracts of P. viridis shows highest activity against P. mirabilis (8 mm), 14:6, 4:16 and 2:18 fractions showed prominent activity against P. aeruginosa, E.coli and K. pneumoniae. In C. madrasensis also 10:10 fraction showed highest activity E. coli, P. aeruginosa and S. aureus. The 18:2, 12:8 and 2:18 fractionated extracts of C. madrasensis exhibits effective activity against S. aureus, S. typhi and E. coli. Water, ethanol and methanol extracts showed antibacterial activity against all most all the bacteria tested. Compare to water extracts, ethanol and methanol extracts showed more activity against all pathogens.
  Samanta Saha , R. Thavasi and S. Jayalakshmi
  This study deals with isolation and identification of Pseudomonas aeruginosa from marine environment for phenazine pigment production. Pigment production results revealed that, the strain could able to produce two different pigments namely, pyocyanin and pyorubrin. Maximum biomass was observed at 66 h of incubation, but the pigment production seems to be continuous throughout the culture period (72 h). Antibacterial activity of the pigments was evaluated against pathogenic bacteria, maximum growth inhibitory activity was observed with pyocyanin and pyorubrin at 20 μL concentration (1.7 and 1.3 cm, respectively) against Citrobacter sp. Hemolytic activity of the pigments inferred that, hemolysis was observed with both pigments at 15, 20 and 25 μL concentration and no hemolysis was found at 5, 10 and 15 μL. The pigments were evaluated for their potential as food colourants with agar. Pleasant colouration was observed with pyocyanin and pyorubrin at 25 mg mLG-1 concentration.
  R. Thavasi , S. Jayalakshmi , T. Balasubramanian and Ibrahim M. Banat
  The present study deals with the hydrocarbon degrading potential of a marine nitrogen fixing bacterium Azotobacter chroococcum isolated from Tuticorin harbor (Lat. 08o45`N; Long. 78o13`E). Degradation of crude oil (58%) and emulsification (D610) of waste motor oil (1.51), crude oil (1.43), pea nut oil (1.39), diesel (0.69), kerosene (0.81), Naphthalane (0.36), Anthracene (0.33) and xylene (0.42) indicated its potentiality in utilization of various hydrocarbons. Growth of Azotobacter chroococcum in a mineral medium with 0.5% crude oil as sole carbon source resulted maximum cell density at 96 h with an OD value of 0.333. At the end of 96 h, the cell count was 4.5x109 CFU mL-1 and 2.5 mg mL-1 of biomass. The biosurfactant production was found to be 1 mg mL-1 at 96 h. The total nitrogen fixed was 4.2 mg L-1. Two plasmids were found with molecular weight of 4788 and 2400 base pairs, respectively. Loss of biodegradation and biosurfactant production after plasmid curing was observed, which confirmed that, the biosurfactant production and biodegradation process were plasmid mediated. Results of the present study revealed the possibility of using marine nitrogen fixing hydrocarbon degrading bacteria and their biosurfactants in the abatement of marine oil pollution.
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