铁呼吸细菌Shewanella统筹呼吸作用的新机制及其环境意义的研究

Based on their unique respiration, iron reducing bacteria (IRB) not only play a role in the biogeochemical cycling of many elements, but also are used for bioremediation and energy production. IRB maintain an electron transfer web for anaerobic and aerobic respiration under aerobic condition. It is still unknown how such an energy- and nutrient-consuming regulation has retained under selection pressure. We have previously reported an oxygen-regulated transcription factor FlrA in model IRB Shewanella. RNA-Seq analysis showed that FlrA inhibits aerobic respiration while activates anaerobic respiration under the aerobic condition. These results suggested that FlrA is the key factor to control the aerobic and anaerobic respiration. In this study, we will illustrate how FlrA orchestrates expression of genes involved in respiration in response to available electron acceptors. First, we will distinguish genes that are directly and indirectly regulated by FlrA, and reveal the underlying transcription regulation. Second, we will test the influence of common electron acceptors in FlrA expression as well as the underlying mechanism. Third, we will evaluate the effect of FlrA on the fitness of Shewanella in response to electron acceptors. In summary, this study will deepen our understanding of the biological and environmental significance of IRB respiration and underlying regulation.

独特的呼吸作用是铁呼吸细菌(IRB)推动元素循环、作为生物修复和能源微生物的关键。IRB同时维持有氧和厌氧呼吸的电子传递链，耗费能量和营养，却为何未被选择压力淘汰，目前尚不清楚。课题组前期报道了模式IRB Shewanella中受氧气调控的转录因子FlrA。RNA-Seq显示有氧条件下，FlrA激活厌氧呼吸而抑制有氧呼吸，是控制上述现象的新型呼吸调控因子。基于此，本项目拟围绕FlrA的调控与被调控机制及生物学作用展开：①结合ChIP-Seq和RNA-Seq，区分FlrA直接和间接调控的基因；分析直接调控的分子机制；突变体库筛选介导间接调控的中间基因。②分析不同电子受体对FlrA表达的影响；筛选介导该影响的基因。③通过竞争实验，分析FlrA对Shewanella适应和利用三种常见电子受体的作用。通过解析FlrA响应电子受体以统筹呼吸和环境适应的机制，深化对IRB呼吸作用生物和环境意义的认识。

希瓦氏菌作为模式环境细菌，因多样的呼吸途径，不仅在多种元素的生物地球化学循环中发挥作用，而且是废水资源化和污染的微生物修复等应用的工程出发菌株。然后对希瓦氏菌呼吸途径的切换和调控机制认识仍然有限。针对这一基础生物学问题，本项目在前期发现的呼吸调控因子的基础上，解析了该调控因子的调控单元(regulon)。发现该调控因子不仅控制有氧呼吸电子传递链的复合物I、终端氧化酶和三羧酸循环基因的表达，而且控制厌氧呼吸多种电子受体还原的终端氧化酶和氢酶的表达。我们发现在众多受调控的基因中Fe-S蛋白合成相关基因YggX是有氧生长的必须基因，而YggX缺失导致希瓦氏菌在有氧生长时呈现营养缺陷型。这些与肠杆菌中YggX的生理影响存在很大差异。此外，在对呼吸调控因子regulon的分析中，我们阐明了有氧呼吸相关基因在所属细菌生态分布中的意义。这些研究结果，部分发表于环境微生物领域的Top期刊Applied and Environmental Microbiology，部分正在投稿中。