Cr(VI) reduction by an extracellular polymeric substance (EPS) produced from a strain of Pseudochrobactrum saccharolyticum

Abstract

A better understanding of the Cr(VI) reduction position and mechanisms by a Cr(VI)-reducing strain is important for the bioremediation of Cr pollution in the environment. In the present study, we were interested in figuring out the role of extracellular polymeric substances (EPS) as the main area for Cr(VI) reduction in the newly reported strain of Pseudochrobactrum saccharolyticum LY10. We investigated the subcellular distribution and reduction capability of each cellular component as the main area of Cr(VI) reduction by scanning electron microscopy and soft X-ray spectromicroscopy. The results suggested that most of Cr was presented in the supernatants as Cr(III) after reduction. In the cells, Cr was mostly distributed in the EPS and cell wall, while the EPS had the maximum Cr(VI) reduction rate (81.5%) as compared with the cell wall (30.1%). Soft X-ray spectromicroscopy analysis indicated that Cr accumulated more in the EPS. Therefore, the results suggested that the EPS were the main area for Cr(VI) reduction in the bacteria of P. saccharolyticum LY10.

Keywords: Cr(VI) reduction; EPS; Pseudochrobactrum saccharolyticum LY10; Soft X-ray spectromicroscopy; Subcellular distribution.

Fig. 1

Distribution profiles of Cr in different fractions of P. saccharolyticum LY10 culture (a distribution in supernatant; b the subcellular distribution profile of Cr in cells)

Fig. 2

The Cr(VI)-reducing abilities of different subcellular fractions of P. saccharolyticum LY10 [experiments were conducted with initial 5.2 mg L^− 1 Cr(VI)]

Fig. 3

SEM images of P. saccharolyticum LY10 cells [a cells were not treated with Cr(VI); b cells were incubated with 55 mg L^− 1 Cr(VI); c 110 mg L^− 1 Cr(VI); d 220 mg L^− 1 Cr(VI)]

Fig. 4

Morphology of a single P. saccharolyticum LY10 cell by soft X-ray spectromicroscopy analysis (3.3 µm × 3.3 µm)

Fig. 5

The distribution of different Cr species in a single cell of P. saccharolyticum LY10 by soft X-ray spectromicroscopy analysis (24 h: 3.3 µm × 3.3 µm; 48 h: 3.3 µm × 5.4 µm)