Enhanced recovery of hexavalent chromium by remodeling extracellular polymeric substances through engineering Agrobacterium tumefaciens F2

Abstract Commonly used modification of materials added the operational complexity and was unsustainable for enhanced chromium recovery. Bioengineering was applied for enhancing Cr(VI) recovery in a facile and green manner. The engineered strain F2-exoY-O produced a significantly higher level of EPSs (1219 mg/L) containing more polysaccharide (59.1%) than that (44.3% polysaccharide in 686 mg/L EPSs) by wild strain F2. The proportion of glucose and galactose increased in polysaccharide in EPSs produced by F2-exoY-O. Control EPSs (411.6 mg/L) produced by wild strain F2 showed 70.5% Cr(VI) recovery at pH 3.0, by contrast, EPSs produced by engineered strain F2-exoY-O reached 88.5% at the same conditions. A minor Cr(III) existed in the aqueous solution after chromium recovery by EPS, accompanied by the increased solution pH. X-ray photoelectron spectroscopy showed that Cr(VI) was the main form on EPS with a minor Cr(III). Fourier transform infrared spectra suggested that polysaccharides (i.e. mainly hemiacetal groups) in EPSs were major participants in Cr(VI) recovery. Chelation between functional groups on EPS and Cr(VI) was the main recovery mechanism, along with a minor reduction of Cr(VI) into Cr(III) on EPSs. The enhanced recovery performance was attributed to the increased polysaccharide in EPSs produced by engineered strain F2-exoY-O. Cr(VI) recovery was enhanced by bioengineering method, providing a facile, effective and sustainable way for the preservation of chromium resource.