Abstract
Microbial nanowires (MNWs) can play an important role in the transformation and mobility of toxic metals/metalloids in environment. The potential role of MNWs in cell-arsenic (As) interactions has not been reported in microorganisms and thus we explored this interaction using Synechocystis PCC 6803 as a model system. The effect of half maximal inhibitory concentration (IC50) [~300 mM As (V) and ~4 mM As (III)] and non-inhibitory [4X lower than IC50, i.e., 75 mM As (V) and 1 mM As (III)] of As was studied on Synechocystis cells in relation to its effect on Chlorophyll (Chl) a, type IV pili (TFP)-As interaction and intracellular/extracellular presence of As. In silico analysis showed that subunit PilA1 of electrically conductive TFP, i.e., microbial nanowires of Synechocystis have putative binding sites for As. In agreement with in silico analysis, transmission electron microscopy analysis showed that As was deposited on Synechocystis nanowires at all tested concentrations. The potential of Synechocystis nanowires to immobilize As can be further enhanced and evaluated on a large scale and thus can be applied for bioremediation studies.
Highlights
Arsenic (As) is one of the most widely distributed toxic elements on earth and has become a major cause of concern in recent years due to increased human activities like mining, well-drilling, pesticide use, burning of fossil fuels, etc. (Yin et al, 2011; Shen et al, 2013)
Cell-As interactions have been widely studied in different cyanobacteria (Huang et al, 2014) and Synechocystis PCC 6803 is known to have an intricate machinery involving enzymes [e.g., As (V) reductase, methylase, etc.], transporters etc. to interact with As (Lopez-Maury et al, 2003)
For surface analysis using transmission electron microscope (TEM)-energy dispersive X-ray spectroscopy (EDX), cells were washed with PBS once at 4000 rpm for 5 min
Summary
Arsenic (As) is one of the most widely distributed toxic elements on earth and has become a major cause of concern in recent years due to increased human activities like mining, well-drilling, pesticide use, burning of fossil fuels, etc. (Yin et al, 2011; Shen et al, 2013). The conversion of As (V) to As (III) and its subsequent efflux from the cells is one of the major As detoxification mechanisms in Synechocystis (Zhang et al, 2013; Sánchez-Riego et al, 2014). This sophisticated machinery may give Synechocystis an ability to tolerate relatively high levels of As compared to other cyanobacteria (Wang et al, 2013; Huang et al, 2014) and implies that it might be playing an important role in As biogeochemistry (Yin et al, 2011). This study describes the intracellular and extracellular morphological changes induced by As and indicates a potential role of Synechocystis TFP in cell-As interactions
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