No abstract

Ni–ferrite-decorated anode enhanced the MPD by 26% to 806.4 mW m−2.

The filamentous cyanobacterium Anabaena fixes nitrogen in specialized cells called heterocysts. The immediate product of fixation, ammonia, is known to be assimilated by addition to glutamate to make glutamine. How fixed nitrogen is transported along the filament to the 10 to 20 vegetative cells that separate heterocysts is unknown. N-fixing heterocysts accumulate an insoluble polymer containing aspartate and arginine at the cell poles. Lockau's group has proposed that the polymer is degraded at the poles to provide a mobile carrier, arginine, to the vegetative cells (R. Richter, M. Hejazi, R. Kraft, K. Ziegler, and W. Lockau, Eur. J. Biochem. 263:163-169, 1999). We wished to use the Sakaguchi reaction for arginine to determine the relative cellular concentration of arginine along the filament. At present, the methods for measuring absorption of the Sakaguchi reaction product at 520 nm are insufficiently sensitive for that purpose. However, that product quenches the fluorescence of phycobiliproteins, which we have adapted to a determination of arginine. Our results are consistent with the proposal that arginine is a principal nitrogen carrier from heterocysts to vegetative cells in Anabaena.

Poor energy output and high cost are the key factors to inhibit the development and application of microbial fuel cells (MFCs). Different types of modification techniques for anode material are suggested to improve power performance in MFCs. nanoFe2O3 is characteristics of no toxicity, biocompatibility and low cost. In this work, stainless steel mesh (SSM), ultracapacitor activated carbon with SSM (AcM), Fe2O3 added AcM (AMF) anodes are investigated to improve MFCs performance. The highest maximum power density (806 ± 26 mW·m-2) is obtained in AMF anode, which is 11 % higher than that of AcM (730 ± 27 mW·m-2), and 57 folds higher than that of SSM anode (12 ± 0.7 mW·m-2). The semi-conducting properties of passive film on the anode surface play a rather important role in anodic reaction by Mott-Schottky analysis. Tafel test demonstrates that the exchange current density (8.36×10-4 A·m-2) is improved by 20 % for AMF compared with AcM control (6.93×10-4 A·m-2). These results show AcM is suitable as MFCs anode, and further addition of Fe2O3 can increase the extracellular electron transfer in that way increase power production in MFCs.

Filamentous Anabaena PCC 7120 differentiates nitrogen-fixing specialized cells called heterocysts at regular intervals following removal of combined nitrogen from the medium. Phycobiliproteins are degraded during differentiation. Heterocyst differentiation was followed at the single cell level by using confocal fluorescence microscopy. The presence of an enhanced fluorescence emission peak from allophycocyanin (APC) indicates that the degradation of the phycobilisomes during nitrogen deprivation possibly initiates at the linker between APC and photosystem II in a bottom-to-top disassembly model. Furthermore, the fluorescence emission peak around 650 nm provides an advantageous marker to identify early candidates for differentiation.