Evidence of specialized bromate-reducing bacteria in a hollow fiber membrane biofilm reactor

Abstract

Bromate is a carcinogenic disinfection by-product formed from bromide during ozonation or advanced oxidation. We previously observed bromate reduction in a hydrogen-based, denitrifying hollow fiber membrane biofilm reactor (MBfR). In this research, we investigated the potential existence of specialized bromate-reducing bacteria. Using denaturing gradient gel electrophoresis (DGGE), we compared the microbial ecology of two denitrifying MBfRs, one amended with nitrate as the electron acceptor and the other with nitrate plus bromate. The DGGE results showed that bromate exerted a selective pressure for a putative, specialized bromate-reducing bacterium, which developed a strong presence only in the reactor with bromate. To gain further insight into the capabilities of specialized, bromate-reducing bacteria, we explored bromate reduction in a control MBfR without any primary electron acceptors. A grown biofilm in the control MBfR reduced bromate without previous exposure, but the rate of reduction decreased over time, especially after perturbations resulting in biomass loss. The decrease in bromate reduction may have been the result of the toxic effects of bromate. We also used batch tests of the perchlorate-reducing pure culture, Dechloromonas sp. PC1 to test bromate reduction and growth. Bromate was reduced without measurable growth. Based on these results, we speculate bromate's selective pressure for the putative, specialized BRB observed in the DGGE was not growth related, but possibly based on resistance to bromate toxicity.

Biological Bromate Reduction Driven by Methane in a Membrane Biofilm Reactor

“…The perchlorate reducing bacterium Dechloromonas sp. PC1 was also reported to reduce bromate without measurable growth . In addition, bromate was reduced to bromide via mediation of nitrate reductase in denitrifying Pseudomonas spp .…”

“…PC1 was also reported to reduce bromate without measurable growth. 35 In addition, was reduced to bromide via mediation of nitrate reductase in denitrifying Pseudomonas spp. 27 Given that nitrate was not provided in stage II, unique conditions (e.g., oxygen-limiting and only bromate fed as the electron acceptor) in the MBfR might select a specialized bromate-reducing bacterium, which warrants further studies.…”

Bromate Reduction by Rhodococcus sp. Br-6 in the Presence of Multiple Redox Mediators

“…32,33 On the other hand, the existence of specific bromate-reducing bacteria has been proposed in several studies. 8,34,35 For example, van Ginkel et al 8 enriched a bromate-reducing mixed microbial culture that utilized bromate as the sole electron acceptor for growth. However, there are still many uncertainties regarding bacterial bromate reduction, mainly because of the limited number of available isolates.…”

“…Certain denitrifiers ,− and chlorate-reducers can reduce bromate in a cometabolic manner, since bromate can be recognized as a substrate by nitrate reductase , and chlorate reductase. , On the other hand, the existence of specific bromate-reducing bacteria has been proposed in several studies. ,, For example, van Ginkel et al enriched a bromate-reducing mixed microbial culture that utilized bromate as the sole electron acceptor for growth. However, there are still many uncertainties regarding bacterial bromate reduction, mainly because of the limited number of available isolates.…”

Complete bromate and nitrate reduction using hydrogen as the sole electron donor in a rotating biofilm-electrode reactor

“…In the past decades, a lot of methods have been successfully implemented to remove bromate, such as adsorption process [4,5], membrane separation [6,7], catalytic decomposition [8][9][10] and biological reduction [11,12]. Among them, biological reduction is considered to be the a promising alternative due to its ability of reducing bromate to relatively innocuous bromide in a cost-effective way [13].…”