The rod-shaped cells of the bacterium Myxococcus xanthus move uni-directionally and occasionally undergo reversals during which the leading/lagging polarity axis is inverted. Cellular reversals depend on pole-to-pole relocation of motility proteins that localize to the cell poles between reversals. We show that MglA is a Ras-like G-protein and acts as a nucleotide-dependent molecular switch to regulate motility and that MglB represents a novel GTPase-activating protein (GAP) family and is the cognate GAP of MglA. Between reversals, MglA/GTP is restricted to the leading and MglB to the lagging pole defining the leading/lagging polarity axis. For reversals, the Frz chemosensory system induces the relocation of MglA/GTP to the lagging pole causing an inversion of the leading/lagging polarity axis. MglA/GTP stimulates motility by establishing correct polarity of motility proteins between reversals and reversals by inducing their pole-to-pole relocation. Thus, the function of Ras-like G-proteins and their GAPs in regulating cell polarity is found not only in eukaryotes, but also conserved in bacteria.

Photosynthetic microbial fuel cells (PMFCs) are an emerging technology for renewable solar energy conversion. Major efforts have been made to explore the electrogenic activity of cyanobacteria, mostly using practically unsustainable reagents. Here we report on photocurrent generation (≈8.64 μA cm(-2)) from cyanobacteria immobilized on electrodes modified with an efficient electron mediator, an Os(2+/3+) redox polymer. Upon addition of ferricyanide to the electrolyte, cyanobacteria generate the maximum current density of ≈48.2 μA cm(-2).

Studies on biological photovoltaics based on intact organisms are challenging and in most cases include diffusing mediators to facilitate electrochemical communication with electrodes. However, using such mediators is impractical. Instead, surface confined Os‐polymers have been successfully used in electrochemical studies including oxidoreductases and bacterial cells but not with algae. Photoelectrogenic activity of a green alga, Paulschulzia pseudovolvox, immobilized on graphite or Os‐polymer modified graphite is demonstrated. Direct electron transfer is revealed, when no mediator is added, between algae and electrodes with electrons emerging from photolysis of water via the cells to the electrode exhibiting a photocurrent density of 0.02 μA cm−2. Os‐polymers with different redox potentials and structures are used to optimize the energy gap between the photosynthetic complexes of the cells and the Os‐polymers and those of greater solubility, better accessibility with membranes, and relatively higher potentials yielded a photocurrent density of 0.44 μA cm−2. When benzoquinone is included to the electrolyte, the photocurrent density reaches 6.97 μA cm−2. The photocurrent density is improved to 11.50 μA cm−2, when the cells are protected from reactive oxygen species when either superoxide dismutase or catalase is added. When adding an inhibitor specific for photosystem II, diuron, the photocurrent is decreased by 50%.

Biological photovoltaics (BPVs) are emerging as a potential sustainable energy‐generating technology to convert solar energy into electrical energy. Although a great variety of photosynthetic biomaterials were studied in BPVs, cyanobacteria are considered as superior candidates because of their simpler physiology. To facilitate extracellular electron transfer (EET) from cyanobacteria to electrodes is the greatest challenge to improving the performance of BPVs. However, a systematic study comparing the photo‐excited EET from such organisms is not yet reported. Here we report on a comparison of photocurrent density generated by benthic cyanobacteria, that is, two species of Leptolyngbya sp. (CAWBG62 and CAWBG100), one species from the order Chroococcales (CAWBG64), and a eukaryotic algae, Paulschulzia pseudovolvox (UKE). This algae and CAWBG100 were sourced from New Zealand, CAWBG62 and CAWBG64 were from Antarctica. We demonstrate EET mediated by three different electron transfer (ET) mediating systems on graphite electrodes. These are as follows: (I) [Os(2,2’‐(bipyridine)2(polyvinyl‐imidazole)10Cl]+/2+ (1:9) [Os‐(bpy)PVI] (II) p‐benzoquinone (PBQ) (III) [Os‐(bpy)PVI] together with PBQ. The maximum photocurrent density of 47.2 μA cm−2 was obtained from CAWBG64 mediated by (III) [Os‐(bpy)PVI] together with PBQ.

NADH:quinone oxidoreductase or complex I is a large membrane bound enzyme complex that has evolved from the combination of smaller functional building blocks. Intermediate size enzyme complexes exist in nature that comprise some, but not all of the protein subunits in full size 14-subunit complex I. The membrane spanning complex I subunits NuoL, NuoM and NuoN are homologous to each other and to two proteins from one particular class of Na(+)/H(+) antiporters, denoted MrpA and MrpD. In complex I, these ion transporter protein subunits are prime candidates for harboring important parts of the proton pumping machinery. Using a model system, consisting of Bacillus subtilis MrpA and MrpD deletion strains and a low copy expression plasmid, it was recently demonstrated that NuoN can rescue the strain deleted for MrpD but not that deleted for MrpA, whereas the opposite tendency was seen for NuoL. This demonstrated that the MrpA-type and MrpD-type proteins have unique functional specializations. In this work, the corresponding antiporter-like protein subunits from the smaller enzymes evolutionarily related to complex I were tested in the same model system. The subunits from 11-subunit complex I from Bacillus cereus behaved essentially as those from full size complex I, corroborating that this enzyme should be regarded as a bona fide complex I. The hydrogenase-3 and hydrogenase-4 antiporter-like proteins on the other hand, could substitute equally well for MrpA or MrpD at pH7.4, suggesting that these enzymes have intermediate forms of the antiporter-like proteins, which seemingly lack the functional specificity.