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The transfer of photoenergized electrons from extracellular photosensitizers across a bacterial cell envelope to drive intracellular chemical transformations represents an attractive way to harness nature's catalytic machinery for solar‐assisted chemical synthesis. In Shewanella oneidensis MR‐1 (MR‐1), trans‐outer‐membrane electron transfer is performed by the extracellular cytochromes MtrC and OmcA acting together with the outer‐membrane‐spanning porin⋅cytochrome complex (MtrAB). Here we demonstrate photoreduction of solutions of MtrC, OmcA, and the MtrCAB complex by soluble photosensitizers: namely, eosin Y, fluorescein, proflavine, flavin, and adenine dinucleotide, as well as by riboflavin and flavin mononucleotide, two compounds secreted by MR‐1. We show photoreduction of MtrC and OmcA adsorbed on RuII‐dye‐sensitized TiO2 nanoparticles and that these protein‐coated particles perform photocatalytic reduction of solutions of MtrC, OmcA, and MtrCAB. These findings provide a framework for informed development of strategies for using the outer‐membrane‐associated cytochromes of MR‐1 for solar‐driven microbial synthesis in natural and engineered bacteria.

Many species of bacteria can couple anaerobic growth to the respiratory reduction of insoluble minerals containing Fe(III) or Mn(III/IV). It has been suggested that in Shewanella species electrons cross the outer membrane to extracellular substrates via 'porin-cytochrome' electron transport modules. The molecular structure of an outer-membrane extracellular-facing deca-haem terminus for such a module has recently been resolved. It is debated how, once outside the cells, electrons are transferred from outer-membrane cytochromes to insoluble electron sinks. This may occur directly or by assemblies of cytochromes, perhaps functioning as 'nanowires', or via electron shuttles. Here we review recent work in this field and explore whether it allows for unification of the electron transport mechanisms supporting extracellular mineral respiration in Shewanella that may extend into other genera of Gram-negative bacteria.

The iron responsive regulator Irr is found in a wide range of a-proteobacteria, where it regulates many genes in response to the essential but toxic metal iron. Unlike Fur, the transcriptional regulator that is used for iron homeostasis by almost all other bacterial lineages, Irr does not sense Fe2+ directly, but, rather, interacts with a physiologically important form of iron, namely heme. Recent studies of Irr from the N2-fixing symbiont Rhizobium leguminosarum (IrrRl) showed that it binds heme with submicromolar affinity at a His-Xxx-His (HxH) motif. This caused the protein to dissociate from its cognate DNA regulatory iron control element box sequences, thus allowing expression of its target genes under iron-replete conditions. In the present study, we report new insights into the mechanisms and consequences of heme binding to Irr. In addition to the HxH motif, Irr binds heme at a second, lower-affinity site. Spectroscopic studies of wild-type Irr and His variants show that His46 and probably His66 are involved in coordinating heme in a low-spin state at this second site. By contrast to the well-studied Irr from Bradyrhizobium japonicum, neither heme site of IrrRl stabilizes ferrous heme. Furthermore, we show that heme-free IrrRl exists as a mixture of dimeric and larger, likely hexameric, forms and that heme binding promotes IrrRl oligomerization. Bioanalytical studies of IrrRl variants showed that this property is not dependent on the HxH motif but is associated with heme binding at the second site.

Faith or fear? How we respond to our external environment depends on the emotional and energetic patterns rooted in our Chakras, our seven sacred gates. As spirit in body, our soul constantly pushes us toward harmony within and amongst these centres, bringing them into full expansion. This, then, can lead to balance between the need for connection and courage, choice and resilience, self-love, unconditional love, voice, insight and faith. The emotional imprints of our chakras are excellent maps for discovering unexplored territory. Working with these images, we find that the chakras can intensify and expand, leading us toward soul awareness. As healing tools, Bach Flower Remedies have a powerful and unique and synergistic rapport with the patterns of our chakras and their energy is invaluable in assisting us in this challenging work. Copyright © 2003 Whurr Publishers Ltd.