BackgroundAutoinducer-2 (AI-2) is a universal signal molecule and enables an individual bacteria to communicate with each other and ultimately control behaviors of the population. Harnessing the character of AI-2, two kinds of AI-2 “controller cells” (“consumer cells” and “supplier cells”) were designed to “reprogram” the behaviors of entire population.ResultsFor the consumer cells, genes associated with the uptake and processing of AI-2, which includes LsrACDB, LsrFG, LsrK, were overexpressed in varying combinations. Four consumer cell strains were constructed: Escherichia coli MG1655 pLsrACDB (NK-C1), MG1655 pLsrACDBK (NK-C2), MG1655 pLsrACDBFG (NK-C3) and MG1655 pLsrACDBFGK (NK-C4). The key enzymes responsible for production of AI-2, LuxS and Mtn, were also overexpressed, yielding strains MG1655 pLuxS (NK-SU1), and MG1655 pLuxS-Mtn (NK-SU2). All the consumer cells could decrease the environmental AI-2 concentration. NK-C2 and NK-C4 were most effective in AI-2 uptake and inhibited biofilm formation. While suppliers can increase the environmental AI-2 concentration and NK-SU2 was most effective in supplying AI-2 and facilitated biofilm formation. Further, reporter strain, MG1655 pLGFP was constructed. The expression of green fluorescent protein (GFP) in reporter cells was initiated and guided by AI-2. Mixture of consumer cells and reporter cells suggest that consumer cells can decrease the AI-2 concentration. And the supplier cells were co-cultured with reporter cells, indicating that supplier cells can provide more AI-2 compared to the control.ConclusionsThe consumer cells and supplier cells could be used to regulate environmental AI-2 concentration and the biofilm formation. They can also modulate the AI-2 concentration when they were co-cultured with reporter cells. It can be envisioned that this system will become useful tools in synthetic biology and researching new antimicrobials.Electronic supplementary materialThe online version of this article (10.1186/s12866-017-1107-2) contains supplementary material, which is available to authorized users.

Despite the various strategies for achieving metal–nitrogen–carbon (M–N–C) single-atom catalysts (SACs) with different microenvironments for electrochemical carbon dioxide reduction reaction (CO 2 RR), the synthesis–structure–performance correlation remains elusive due to the lack of well-controlled synthetic approaches. Here, we employed Ni nanoparticles as starting materials for the direct synthesis of nickel (Ni) SACs in one spot through harvesting the interaction between metallic Ni and N atoms in the precursor during the chemical vapor deposition growth of hierarchical N-doped graphene fibers. By combining with first-principle calculations, we found that the Ni-N configuration is closely correlated to the N contents in the precursor, in which the acetonitrile with a high N/C ratio favors the formation of Ni-N 3 , while the pyridine with a low N/C ratio is more likely to promote the evolution of Ni-N 2 . Moreover, we revealed that the presence of N favors the formation of H-terminated edge of sp 2 carbon and consequently leads to the formation of graphene fibers consisting of vertically stacked graphene flakes, instead of the traditional growth of carbon nanotubes on Ni nanoparticles. With a high capability in balancing the *COOH formation and *CO desorption, the as-prepared hierarchical N-doped graphene nanofibers with Ni-N 3 sites exhibit a superior CO 2 RR performance compared to that with Ni-N 2 and Ni-N 4 ones.

Cobalt-free LiNiO 2 is an attractive cathode material with high energy density and low cost but suffers from severe structural degradation and poor performance. Here, a molten salt-assisted synthesis combined with a Li-refeeding strategy is proposed to obtain nonstoichiometric Li 1+x Ni 1-x O 2 with submicron particle size and superior rate performance. The slightly Li-rich and single-crystalline characters inhibit Li + /Ni 2+ anti-site defects and mitigates the undesirable phase evolution. Remarkably, single-crystalline Li 1.045 Ni 0.955 O 2 exhibits a high specific capacity (218.7 mAh g −1 at 0.1 C), considerable rate capability (187.0 mAh g −1 at 5 C), and an initial Coulombic efficiency (89.62% at 0.1 C) in the 1.27 Ah pouch full cell employing the graphite anode, significantly outperforming near stoichiometric LiNiO 2 . Furthermore, the particulate morphology of Li 1.045 Ni 0.955 O 2 remains intact at charge voltages up to 4.8 V, whereas near stoichiometric LiNiO 2 features intragranular cracks and irreversible lattice distortion. This study underscores the value of molten salt-assisted synthesis and Li-refeeding modification to upgrade Ni-based layered oxide cathode materials for advanced Li-ion batteries.