Study on the bioremediation of methylene blue by Haematococcus pluvialis through synchrotron-FTIR imaging and spectroscopy.

Methylene blue (MB), as a phenothiazine dye, causes a harmful damage to health and receives increasingly more environmental concern. Herein, the batch experiments for MB biosorption and biotransformation by Haematococcus pluvialis were carried out to evaluate the optimal parameters of MB removal. In this work, we found that the maximum removal efficiency was attained when MB was at the initial concentration of 5 mg/L. Meanwhile, the cellular numbers and pigments decreased dramatically with the rising content of MB. Furthermore, synchrotron-FTIR microscopic imaging is employed here to investigate the interaction between MB dye and algal cells by the measurement of the various vital changes of cellular components involving in the bioremediation of the hazardous dye, which indicated that MB dye as a photosensitizer can trigger the algal transformation from vegetative cells into red cysts by introducing oxidative stress. Accordingly, the dye removal efficiency can be sharply enhanced by the transformed algal cells for the accumulation of astaxanthin or carotenoids. In addition, the FTIR spectroscopy combined with PCA algorithm was further utilized to discriminate various algal status based on their spectral features. As a result, it demonstrates that microscopic imaging and FTIR spectroscopy is a powerful and useful tool to elucidate underlying mechanisms of dye removal by algal cells at high spatial resolution and to evaluate cellular physiological characteristics through multivariate statistical analysis, and it even provides a novel and effective strategy to rapidly screen the potential microalgae for the removal of recalcitrant dyes from wastewater.