2. Academic Validation
  3. Isotope fractionation in atrazine degradation reveals rate-limiting, energy-dependent transport across the cell membrane of gram-negative rhizobium sp. CX-Z

Isotope fractionation in atrazine degradation reveals rate-limiting, energy-dependent transport across the cell membrane of gram-negative rhizobium sp. CX-Z

  • Environ Pollut. 2019 May;248:857-864. doi: 10.1016/j.envpol.2019.02.078.
Songsong Chen 1,  Kai Zhang 2,  Rohit Kumar Jha 2,  Chong Chen 2,  Haiyan Yu 2,  Ying Liu 2,  Limin Ma 3
Affiliations

Affiliations

  • 1 State Key Laboratory of Pollution Control and Resources Reuse, Tongji University, Shanghai, 200092, China; Shanghai Institute of Pollution Control and Ecological Security, Shanghai, 200092, PR China.
  • 2 State Key Laboratory of Pollution Control and Resources Reuse, Tongji University, Shanghai, 200092, China.
  • 3 State Key Laboratory of Pollution Control and Resources Reuse, Tongji University, Shanghai, 200092, China; Shanghai Institute of Pollution Control and Ecological Security, Shanghai, 200092, PR China. Electronic address: [email protected].
PMID: 30856501 DOI: 10.1016/j.envpol.2019.02.078
Abstract

In the biological mass transfer of organic contaminants like atrazine, the cellular membrane limits bioavailability of pesticides. We aimed to illustrate the roles of cellular membrane physiology and substrate uptake (e.g., passive diffusion and energy-dependent transport) on the limitations of bioavailability in atrazine biodegradation by Gram-negative strain Rhizobium sp. CX-Z. Compound-specific stable isotope analysis revealed energy-dependent transport across cellular membrane led to bioavailability limitations in atrazine biotransformation. Carbon isotope fractionation (ε(C) = -1.8 ± 0.3‰) was observed and significantly smaller in atrazine biodegradation by Rhizobium sp. CX-Z than that expected in acid hydrolysis (ε(C) = -4.8 ± 0.4‰) and hydrolysis by the pure Enzyme TrzN (ε(C) = -5.0 ± 0.2‰). However, isotope fractionation was restored in membrane-free cells of Rhizobium sp. CX-Z (ε(C) = -5.4 ± 0.2‰) where no cellular membrane limits substrate uptake. When respiratory chain was inhibited by rotenone, the pseudo-first order kinetic rate constants (0.08 ± 0.03 h-1, 0.09 ± 0.03 h-1) was observed to be statistically less than in the control group (0.23 ± 0.02 h-1, 0.33 ± 0.02 h-1), demonstrating that energy-dependent transport dominated atrazine transfer across the cellular membrane. Therefore, our results revealed energy-dependent transport across cellular membrane existing in Gram-negative strain Rhizobium sp. CX-Z determines bioavailability of atrazine in biotransformation process even at high concentration.

Keywords

Active transport; Atrazine; Bioavailability; Isotope fractionation; Mass transfer.

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