Indoxyl is an intermediate product in the production of indigo and indirubin. There are no studies on the inhibitory effect of indoxyl on microorganism. In this study, it was found that temperature-stress induced the synthesis of intracellular β-glucosidase, which had a great influence on the ratio of indican, indoxyl, indigo and indirubin in Strobilanthes cusia. At 100 ℃, only indican was detected, whereas a large amount of indoxyl was found at 50–70 ℃. HPLC analysis indicated that the use of indoxyl reduced glucose consumption and metabolite production by Staphylococcus aureus. The cells treated with indoxyl had irregular shapes, and fragments of cells were found in SEM images. The images of CLSM suggest that cell morphological changes would be caused by the inhibition of indoxyl on EMs formation. Moreover, indoxyl decreased intracellular ATP content and increased the NAD+/NADH ratio, which promoted the generation of H2O2, damaging cells.

The biological reduction of ferrous ethylenediaminetetraacetic acid (EDTA-FeII-NO and EDTA-FeIII) is an important process in integrated electrobiofilm reduction method, and this method has been regarded as a promising alternative for removing NOx from industrial boiler flue gas. EDTA-FeII-NO and EDTA-FeIII are crucial substrates that should be biologically reduced at a high rate. However, they would inhibit one another’s reduction processes when they are present together, which might limited the further promotion of this integrated method. In this study, an integrated electrobiofilm reduction system with high reduction rate of EDTA-FeII- NO and EDTA-FeIII was established. The microbial communities in electrobiofilms were mainly studied to analyze their changes during the reduction of these two substrates under different conditions. It presents a better performance of substrates- resistance shock loading and high microbial diversities compared with the conventional chemical absorption-biological reduction system. High-throughput sequencing analysis showed that the changes in concentrations of EDTA-FeII-NO and EDTA-FeIII significantly impacted the genera of the microbial community. Alicycliphilus, Enterobacteriaceae and Raoultella were found to be the dominant genera (>25%, respectively) involved in EDTA-FeII-NO reduction. As an EDTA-FeIII reducing bacteria, Chryseobacterium can endure shock loading of substrates. Ochrobactrum can reduce nitrate using electrons and exhibited better stability under shock loading. Furthermore, higher microbial diversity and stable reactor operation could be achieved when the concentrations of EDTA-FeII-NO and EDTA-FeIII approached the same value.