Effects of cadmium sulfide nanoparticles on sulfate bioreduction and oxidative stress in Desulfovibrio desulfuricans

Abstract

Sulfate-containing wastewater has a serious threat to the environment and human health. Microbial technology has great potential for the treatment of sulfate-containing wastewater. It was found that nano-photocatalysts could be used as extracellular electron donors to promote the growth and metabolic activity of non-photosynthetic microorganisms. However, nano-photocatalysts could also induce oxidative stress and damage cells. Therefore, the interaction mechanism between photosynthetic nanocatalysts and non-photosynthetic microorganisms is crucial to determine the regulatory strategies for microbial wastewater treatment technologies. In this paper, the mechanism and regulation strategy of cadmium sulfide nanoparticles (CdS NPs) on the growth of sulfate-reducing bacteria and the sulfate reduction process were investigated. The results showed that the sulfate reduction efficiency could be increased by 6.4% through CdS NPs under light conditions. However, the growth of Desulfovibrio desulfuricans C09 was seriously inhibited by 55% due to the oxidative stress induced by CdS NPs on cells. The biomass and sulfate reduction efficiency could be enhanced by 6.8% and 5.9%, respectively, through external addition of humic acid (HA). At the same time, the mechanism of the CdS NPs strengthening the sulfate reduction process by sulfate bacteria was also studied which can provide important theoretical guidance and technical support for the development of microbial technology combined with extracellular electron transfer (EET) for the treatment of sulfate-containing wastewater.

Keywords: Desulfovibrio desulfuricans; Cadmium sulfide nanoparticles; Extracellular polymeric substances (EPS); Oxidative stress; Sulfate reduction.

Fig. 1

The characteristic of CdS NPs (a UV of CdS NPs; b XRD of CdS NPs; c SEM of CdS NPs)

Fig. 2

The SEM image and its corresponding EDS spectrum of C09 after treatment with CdS NPs. a Without CdS NPs; b with CdS NPs; c EDS of C09 with CdS NPs

Fig. 3

Effects of the CdS NPs on C09 sulfate reduction and growth process. a Sulfate concentration; b Biomass

Fig. 4

Effects of CdS NPs on sulfate reduction, growth and EPS composition of strain. C09 that removed/contained EPS. a Sulfate concentration; b Biomass

Fig. 5

ATR-IR analysis and composition of EPS. a Composition of EPS; b ATR-IR of EPS

Fig. 6.

3D-EEM of extracellular polymeric substance. a without CdS NPs; b with CdS NPs

Fig. 7

Effects of EPS components on the efficiency of sulfate reduction of C09. a Rude EPS and CdS NPs; b without EPS, but with CdS NPs; c EPS with proteinase treatment; d EPS with polysaccharidase treatment; e EPS with both proteinase and polyaccharidase; f EPS with CdS NPs

Fig. 8

Effect of EPS components on instantaneous photo-current intensity. A EPS with proteinase treatment; B EPS with both proteinase and polysaccharidase; C no-added EPS; D EPS with polysaccharidase; E added EPS

Fig. 9

Effect of CdS NPs on growth of C09 and reduction of sulfate under light. a Sulfate concentration at 8 h and 24 h; b Biomass at 8 h and 24 h

Fig. 10

The effects of light intensity on ·OH, intracellular ROS and MDA contents (A ·OH concentration; B Intracellular ROS content; C MDA concentration)

Fig. 11

The effect of adding S²⁻ on the content of ·OH in medium

Fig. 12

Effects of HA on ·OH, intracellular ROS and MDA contents for C09. a ·OH concentration; b Intracellular ROS content; c MDA concentration

Fig. 13

Effects of HA on sulfate reduction and growth of C09. a Sulfate concentration; b Biomass