Abstract：
With the death and decomposition of widely distributed photosynthetic organisms, free natural pigments are often detected in surface water, sediment and soil. Whether free pigments can act as photosensitizers to drive biophotoelectrochemical metabolism in nonphotosynthetic microorganisms has not been reported. In this work, we provide direct evidence for the photoelectrophic relationship between extracellular chlorophyll a (Chl a) and nonphotosynthetic microorganisms. The results show that 10 μg of Chl a can produce significant photoelectrons (∼0.34 A/cm2) upon irradiation to drive nitrate reduction in Shewanella oneidensis. Chl a undergoes structural changes during the photoelectric process, thus the ability of Chl a to generate a photocurrent decreases gradually with increasing illumination time. These changes are greater in the presence of microorganisms than in the absence of microorganisms. Photoelectron transport from Chl a to S. oneidensis occurs through a direct pathway involving the cytochromes MtrA, MtrB, MtrC and CymA but not through an indirect pathway involving riboflavin. These findings reveal a novel photoelectrotrophic linkage between natural photosynthetic pigments and nonphototrophic microorganisms, which has important implications for the biogeochemical cycle of nitrogen in various natural environments where Chl a is distributed.
摘要：
随着广泛分布的光合生物的死亡和分解，在地表水中经常检测到游离的天然色素，沉积物和土壤。尚未报道游离色素是否可以作为光敏剂来驱动非光合微生物中的生物电化学代谢。在这项工作中,我们为细胞外叶绿素a（Chla）与非光合微生物之间的光电关系提供了直接证据。结果表明，10μg的Chla在辐照后可以产生明显的光电子（〜0.34A/cm2），以驱动希瓦氏菌中的硝酸盐还原。Chla在光电过程中经历结构变化，因此，Chla产生光电流的能力随着光照时间的增加而逐渐降低。这些变化在存在微生物的情况下比在不存在微生物的情况下更大。从Chla到S.oneidenis的光电子传输通过涉及细胞色素MtrA的直接途径发生，MtrB,MtrC和CymA，但不通过涉及核黄素的间接途径。这些发现揭示了天然光合色素和非光养微生物之间的新型光电营养联系，这对Chla分布的各种自然环境中氮的生物地球化学循环具有重要意义。
