Nucleotides as Bacterial Second Messengers.

In addition to comprising monomers of nucleic acids, nucleotides have signaling functions and act as second messengers in both prokaryotic and eukaryotic cells. The most common example is cyclic AMP (cAMP). Nucleotide signaling is a focus of great interest in bacteria. Cyclic di-AMP (c-di-AMP), cAMP, and cyclic di-GMP (c-di-GMP) participate in biological events such as bacterial growth, biofilm formation, sporulation, cell differentiation, motility, and virulence. Moreover, the cyclic-di-nucleotides (c-di-nucleotides) produced in pathogenic intracellular bacteria can affect eukaryotic host cells to allow for infection. On the other hand, non-cyclic nucleotide molecules pppGpp and ppGpp are alarmones involved in regulating the bacterial response to nutritional stress; they are also considered second messengers. These second messengers can potentially be used as therapeutic agents because of their immunological functions on eukaryotic cells. In this review, the role of c-di-nucleotides and cAMP as second messengers in different bacterial processes is addressed.

Iron reducing sludge as a source of electroactive bacteria: assessing iron reduction in biofilm bacteria, planktonic cells and isolates from a microbial fuel cell.

In this study, bacteria from a microbial fuel cell (MFC) and isolates were evaluated on their Fe3+ reduction capability at different concentrations of iron using acetate as the sole source of carbon. The results demonstrated that the planktonic cells can reach an iron reduction up to 60% at 27 mmol Fe3+. Azospira oryzae (µ 0.89 ± 0.27 d-1) and Cupriavidus metallidurans CH34 (µ 2.34 ± 0.81 d-1) presented 55 and 62% of Fe3+ reduction, respectively, at 16 mmol l-1. Enterobacter bugandensis (µ 0.4 ± 0.01 d-1) 40% Fe3+ at 27 mmol l-1, Citrobacter freundii ATCC 8090 (µ 0.23 ± 0.05 d-1) and Citrobacter murliniae CDC2970-59 (µ 0.34 ± 0.02 d-1) reduced Fe3+ in ~ 50%, at 55 mmol l-1. This is the first report on these bacteria on a percentage of iron reduction. These results may be useful for anode design to contribute to a higher energy generation in MFCs.