Straub Kristina L, Schink Bernhard
Fachbereich Biologie, Universität Konstanz, 78457 Konstanz, Germany.
Arch Microbiol. 2004 Oct;182(2-3):175-81. doi: 10.1007/s00203-004-0686-0. Epub 2004 Aug 31.
Geobacter species such as G. bremensis, G. pelophilus, and G. sulfurreducens are obligately anaerobic and grow in anoxic, non-reduced medium by fast reduction of soluble ferric citrate. In contrast, insoluble ferrihydrite was either only slowly or not reduced when supplied as electron acceptor in similar growth experiments. Ferrihydrite reduction was stimulated by addition of a reducing agent or by concomitant growth of secondary bacteria that were physiologically and phylogenetically as diverse as Escherichia coli, Lactococcus lactis, or Pseudomonas stutzeri. In control experiments with heat-inactivated Geobacter cells and viable secondary bacteria, no ( E. coli, P. stutzeri) or only little ( L. lactis) ferrihydrite was reduced. Redox indicator dyes showed that growing E. coli, P. stutzeri, or L. lactis cells lowered the redox potential of the medium in a similar way as a reducing agent did. The lowered redox potential was presumably the key factor that stimulated ferrihydrite reduction by all three Geobacter species. The observed differences in anoxic non-reduced medium with ferric citrate versus ferrihydrite as electron acceptor indicated that reduction of these electron acceptors involved different cellular components or different biochemical strategies. Furthermore, it appears that redox-sensitive components are involved, and/or that gene expression of components needed for ferrihydrite reduction is controlled by the redox state.
诸如布氏地杆菌、嗜泥地杆菌和硫还原地杆菌等一些地杆菌属物种是专性厌氧菌，它们在缺氧、未还原的培养基中通过快速还原可溶性柠檬酸铁而生长。相比之下，在类似的生长实验中，当以不溶性水铁矿作为电子受体时，其还原速度要么很慢，要么根本不发生还原。添加还原剂或与生理和系统发育上各不相同的次生细菌（如大肠杆菌、乳酸乳球菌或施氏假单胞菌）共同生长，可刺激水铁矿的还原。在使用热灭活的地杆菌细胞和活的次生细菌进行的对照实验中，没有（大肠杆菌、施氏假单胞菌）或只有少量（乳酸乳球菌）水铁矿被还原。氧化还原指示剂染料表明，生长中的大肠杆菌、施氏假单胞菌或乳酸乳球菌细胞降低培养基氧化还原电位的方式与还原剂类似。降低的氧化还原电位可能是刺激所有三种地杆菌还原水铁矿的关键因素。在以柠檬酸铁和水铁矿作为电子受体的缺氧未还原培养基中观察到的差异表明，这些电子受体的还原涉及不同的细胞成分或不同的生化策略。此外，似乎涉及对氧化还原敏感的成分，和/或水铁矿还原所需成分的基因表达受氧化还原状态控制。
