Abstract：
Competition and cooperation between denitrification and Cr(VI) reduction in a H2-based membrane biofilm reactor (H2-MBfR) were documented over 55 days of continuous operation. When nitrate (5 mg N/L) and chromate (0.5 mg Cr/L) were fed together, the H2-MBfR maintained approximately 100 % nitrate removal and 60 % chromate Cr(VI) removal, which means that nitrate outcompeted Cr(VI) for electrons from H2 oxidation. Removing nitrate from the influent led to an immediate increase in Cr(VI) removal (to 92 %), but Cr(VI) removal gradually deteriorated, with the removal ratio dropping to 14 % after five days. Cr(VI) removal resumed once nitrate was again added to the influent. 16S rDNA analyses showed that bacteria able to carry out H2-based denitrification and Cr(VI) reduction were in similar abundances throughout the experiment, but gene expression for Cr(VI)-reduction and export shifted. Functional genes encoding for energy-consuming chromate export (encoded by ChrA) as a means of bacterial resistance to toxicity were more abundant than genes encoding for the energy producing Cr(VI) respiration via the chromate reductase ChrR-NdFr. Thus, Cr(VI) transport and resistance to Cr(VI) toxicity depended on H2-based denitrification to supply energy. With Cr(VI) being exported from the cells, Cr(VI) reduction to Cr(III) was sustained. Thus, cooperation among H2-based denitrification, Cr(VI) export, and Cr(VI) reduction led to sustained Cr(VI) removal in the presence of nitrate, even though Cr(VI) reduction was at a competitive disadvantage for utilizing electrons from H2 oxidation.
摘要：
在连续运行55天的过程中，记录了基于H2的膜生物膜反应器（H2-MBfR）中反硝化与Cr（VI）还原之间的竞争与合作。当硝酸盐（5mgN/L）和铬酸盐（0.5mgCr/L）一起饲喂时，H2-MBfR保持约100%硝酸盐去除和60%铬酸盐Cr(VI)去除，这意味着硝酸盐对H2氧化的电子竞争超过Cr（VI）。从流入物中去除硝酸盐导致Cr(VI)去除率立即增加(至92%)，但Cr(VI)的去除逐渐恶化,五天后去除率降至14%。一旦将硝酸盐再次添加到流入物中,就恢复Cr(VI)去除。16SrDNA分析表明，在整个实验中，能够进行基于H2的反硝化和Cr（VI）还原的细菌的丰度相似，但是Cr（VI）减少和输出的基因表达发生了变化。编码消耗能量的铬酸盐输出（由ChrA编码）作为细菌对毒性的抗性的功能基因比编码通过铬酸盐还原酶ChrR-NdFr产生能量的Cr（VI）呼吸的基因更丰富。因此，Cr（VI）的传输和对Cr（VI）毒性的抗性取决于基于H2的反硝化来提供能量。随着Cr(VI)从细胞中输出，Cr(VI)持续还原为Cr(III)。因此，H2脱氮之间的合作，Cr(VI)出口，和Cr（VI）还原导致在硝酸盐存在下持续的Cr（VI）去除，即使Cr（VI）还原在利用H2氧化的电子方面处于竞争劣势。
