Hematite is usually considered as a terminal electron acceptor for dissimilatory metal-reducing bacteria (DMRB), such as Shewanella oneidensis MR-1. However, hematite is also a semiconductor with visible light response. How the photocatalytic activity of hematite affects its electrical interplay with DMRB, as well as its role in relevant biogeochemical processes under sunlight, is still unclear. In this study, we investigated the effect of hematite on Cr(VI) removal by S. oneidensis MR-1 in the dark versus under stimulated sunlight using both batch experiments and photoelectrochemical analysis in a solar-assisted microbial photoelectrochemical system with a hematite photoanode covered by S. oneidensis MR-1. Under the dark conditions, hematite at low mineral-to-cell ratios can promote Cr(VI) removal through adsorbing both Cr(VI) and bacteria on/near hematite surface, which facilitates Cr(VI) bio-reduction and also alleviates self-poisoning processes of cells with time. However, as mineral-to-cell ratios reach a high level, hematite particles may cover cell surface and impact Cr(VI) bio-reduction, leading to the decreased Cr(VI) removal with increasing hematite particles. Under simulated sunlight, S. oneidensis MR-1 generates electrons from lactate metabolism and utilizes them to fill photoexcited holes in hematite, generating photoexcited electrons to reduce Cr(VI). Thus, in addition to directly enzymatic reduction of Cr(VI), the new light-triggered electron transfer pathway: lactate → S. oneidensis MR-1 → hematite → Cr(VI) further increases Cr(VI) removal and lactate metabolism. Also, the time-dependent cell survival is increased by the presence of hematite under the simulated sunlight, probably owing to the promoted Cr(VI) reduction and accumulation of Cr(III)-products on hematite surface. Moreover, organic hole scavenger, such as Ethylenediaminetetraacetic acid (EDTA), can further enhance Cr(VI) removal by hematite and S. oneidensis MR-1 under light irradiation. The photoelectrochemical results confirm that the light-triggered electron transfer pathway can be promptly and repeatedly produced upon illumination, and the rapid decrease of photocurrents after spiking Cr(VI) indicates Cr(VI) reduction by the photogenerated electrons from hematite. These findings suggest that semiconducting minerals, like hematite, can harvest solar energy to boost microbial metabolism and contaminant transformation by non-phototrophic, electroactive bacteria, which in turn increases bacterial tolerance toward toxic compounds in surrounding environments.

赤铁矿通常被认为是异化金属还原细菌（DMRB）（如Shewanella oneidensis MR-1 ）的末端电子受体。但是，赤铁矿还是具有可见光响应的半导体。赤铁矿的光催化活性如何影响其与DMRB的电相互作用以及在阳光下其在相关生物地球化学过程中的作用尚不清楚。在这项研究中，我们调查了赤铁矿对S去除Cr（VI）的影响。在太阳辅助微生物光电化学体系中，赤铁矿覆盖有S的太阳辅助微生物光电化学系统中，使用批处理实验和光电化学分析，在黑暗和刺激的阳光下对oneidensis MR-1进行了分析。奥尼迪斯MR-1。在黑暗条件下，低矿物质/细胞比率的赤铁矿可通过将Cr（VI）和细菌吸附在赤铁矿表面上/附近来促进Cr（VI）的去除，从而促进Cr（VI）的生物还原并减轻自我随着时间的流逝中毒的细胞。但是，由于矿物质与细胞的比率达到很高的水平，赤铁矿颗粒可能会覆盖细胞表面并影响Cr（VI）的生物还原，从而导致赤铁矿颗粒的去除会降低Cr（VI）的去除率。在模拟阳光下，S。奥尼迪斯MR-1通过乳酸代谢产生电子，并利用它们填充赤铁矿中的光激发空穴，产生光激发电子以还原Cr（VI）。因此，除了直接酶促还原Cr（VI）外，新的光触发电子转移途径为：乳酸→  S。oneidensis MR-1→赤铁矿→Cr（VI）进一步增加了Cr（VI）的去除和乳酸的代谢。同样，在模拟的阳光下，赤铁矿的存在增加了时间依赖性的细胞存活，这可能是由于促进的Cr（VI）还原和六价铬产物在赤铁矿表面的积累。此外，有机空穴清除剂，例如乙二胺四乙酸（EDTA），可以进一步提高赤铁矿和S对Cr（VI）的去除。奥尼迪斯MR-1在光照射下。光电化学结果证实，在照明时可以迅速且重复地产生光触发的电子传输路径，并且在刺穿Cr（VI）后光电流的快速降低表明赤铁矿产生的光生电子会还原Cr（VI）。这些发现表明，像赤铁矿这样的半导体矿物质可以通过利用非光养性电活性细菌来收集太阳能，从而促进微生物的代谢和污染物转化，从而提高细菌对周围环境中有毒化合物的耐受性。