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Assessing the Susceptibility of Bacillus Subtilis to the Toxic effects of two lower Molecular Weight Phthalate Congeners in Pure Culture

Author Affiliations

  • 1State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences, Wuhan 430074, CHINA
  • 2 School of Civil and Environmental Engineering, and National “International Cooperation Base on Environment and Energy”, University of Science and Technology Beijing, Beijing 100084, P.R. CHINA
  • 3 Chemistry Department, Fourah Bay College, University of Sierra Leone, Freetown, SIERRA LEONE

Int. Res. J. Environment Sci., Volume 2, Issue (9), Pages 45-52, September,22 (2013)

Abstract

Microbial degradation of phthalate esters has been proffered as one the most effective processes of remediating environmental media polluted by these ubiquitous compounds in the environment. A number of previous studies have shown Bacillus subtilis among a host of other soil bacteria to metabolize phthalates, however, the reported toxicity of phthalates to microbial life especially at certain levels of pollution could be a deterrent to this process. The nature of interaction between a pollutant and a bacterium depends on both the chemical properties of the pollutant and the metabolic characteristics of the bacterium. This work seeks to investigate the susceptibility of B. subtilis as a model soil microbe to the toxic effects of two lower molecular weight phthalate congeners (Dimethyl phthalate, DMP and Diethyl phthalate, DEP) using a combination of methods that examine the metabolic heat response and morphological changes of the bacterial cells in different dose of the phthalates both aqueous media. Microcalorimetry assessment suggests the phthalates stimulated growth and metabolic activities of the bacteria at doses between 50-100g/mL but however produced inhibitory effects at higher doses. The half inhibitory dose index (ID50) obtained from the metabolic heat response shows that DMP is relatively more toxic to the bacterium than DEP which is attributed to the slightly higher solubility of DMP permitting its easier mobility across cell membrane. Scanning electron microscopic images of cells incubated at different doses of the phthalates show that both DMP and DEP impeded the bacterial growth and reproductive process especially at doses 200g/mL. Comparing these results to previous studies, lower molecular weight phthalates show relatively higher toxicity to B. subtilis than their higher molecular weight congeners. These evidences show that within certain low doses, phthalates can serve as carbon or energy sources to microbes by stimulating their metabolic activities but beyond certain limits, can exhibit their toxic effects by inhibiting microbial growth.

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