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    • "For instance, when P162S/F211S, G207S and L200I strains are exposed to terbuthylazine, only L200I will demonstrate fast and high reduction in its photosynthetic activity, while in the presence of atrazine only the double mutant P162S/F211S will maintain high PSII electron transport efficiency. In a recent review, Hernández-Allica et al. [5] described the successful development of a fibre optic biosensor based on the comparative response of herbicides sensitive and resistant genotypes. This data reiterates the benefits of using resistant strains to improve the specificity of whole-cell based biosensors. "
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    ABSTRACT: This study was prompted by increasing concerns about ecological damage and human health threats derived by persistent contamination of water and soil with herbicides, and emerging of bio-sensing technology as powerful, fast and efficient tool for the identification of such hazards. This work is aimed at overcoming principal limitations negatively affecting the whole-cell-based biosensors performance due to inadequate stability and sensitivity of the bio-recognition element. The novel bio-sensing elements for the detection of herbicides were generated exploiting the power of molecular engineering in order to improve the performance of photosynthetic complexes. The new phenotypes were produced by an in vitro directed evolution strategy targeted at the photosystem II (PSII) D1 protein of Chlamydomonas reinhardtii, using exposures to radical-generating ionizing radiation as selection pressure. These tools proved successful to identify D1 mutations conferring enhanced stability, tolerance to free-radical-associated stress and competence for herbicide perception. Long-term stability tests of PSII performance revealed the mutants capability to deal with oxidative stress-related conditions. Furthermore, dose-response experiments indicated the strains having increased sensitivity or resistance to triazine and urea type herbicides with I50 values ranging from 6×10(-8) M to 2×10(-6) M. Besides stressing the relevance of several amino acids for PSII photochemistry and herbicide sensing, the possibility to improve the specificity of whole-cell-based biosensors, via coupling herbicide-sensitive with herbicide-resistant strains, was verified.
    Full-text · Article · Apr 2013 · PLoS ONE