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A variety of both Gram-positive and Gram-negative bacteria produce large quantities of indole as an intercellular signal in microbial communities. Biosynthesis of indole is well-studied, and while carbon sources and amino acids are important environmental cues for indole production in Escherichia coli, other environmental factors affecting indole production for this strain are less clear. This study demonstrates that the environmental cue pH is an important factor for indole production that further controls biofilm formation of E. coli. Moreover, E. coli produced a higher level of extracellular indole in the presence of the antibiotics ampicillin and kanamycin, and the increased indole enhanced cell survival during antibiotic stress. Additionally, we found here that temperature is another important factor for indole production; E. coli produces and accumulates a large amount of indole at 50 °C, even at low cell densities. Overall, our results suggest that indole is a stable biological compound, and E. coli may utilize indole to protect itself against other microorganisms.

A practical and simple method was developed to determine the oxygen kinetic and metabolic parameters of cell cultures. The said parameters are the oxygen kinetic constant (Ko2), the maximum specific oxygen uptake rate (qmax), the maximum oxygen yield (Y), the critical dissolved oxygen (DO) (Ccr), and the oxygen maintenance coefficient (mo2). These parameters can be calculated from the results of one batch fermentation run. The fermentation needs to be run at an oxygen-limiting condition, and the profiles of DO and cell density need to be recorded. A demonstration of the use of this method was done by using a yeast, Kluyveromyces marxianus.

The Escherichia coli nar promoter is maximally induced under anaerobic conditions in the presence of nitrate ion or under anaerobic only conditions, depending on the genotype of the E. coli nar promoter. Previously, we found that the E. coli nar promoter has some desirable characteristics as an inducible promoter in the E. coli host strains. In this study, the E. coli nar promoter with lacZ gene at the downstream was cloned onto a broad-host-range Gram-negative vector, pBBR122. It was then induced in some other Gram-negative host strains, such as Agrobacterium, Pseudomonas, and Rhizobium, to determine whether the E. coli nar promoter could be used as an inducible promoter in these strains. From shake-flask experiments it was found that the wild-type E. coli nar promoter cloned onto pBBR122, pNW61, was suppressed under aerobic conditions in an Agrobacterium host strain, was partially induced under microaerobic only conditions, and was maximally induced under microaerobic conditions in the presence of nitrate ion. Whereas the mutant-type E. coli nar promoter cloned onto pBBR122, pNW618, was suppressed under aerobic conditions and was maximally induced under microaerobic conditions, regardless of the presence of nitrate ion. This kind of induction pattern observed for the E. coli nar promoters in the Agrobacterium host strain was similar to that observed for the E. coli nar promoters in the E. coli host strain. On the other hand, it was found that both of the E. coli nar promoters, pNW61 and pNW618, in a Pseudomonas host strain were partially induced under aerobic conditions and were maximally induced under microaerobic conditions, regardless of the presence of nitrate. Finally, it was found that both of the E. coli nar promoters in a Rhizobium host strain were minimally induced, regardless of the presence of oxygen or nitrate ion. Similar induction patterns for the three strains were also observed from fermentor experiments in which the dissolved oxygen (DO) level was tightly controlled. From an evolutionary point of view, the results from the three Gram-negative host strains indicate that the E. coli nar promoter system, including the promoter and regulatory proteins, was best conserved in the Agrobacterium host strain and the least conserved in the Rhizobium host strain. From an industrial point of view, the results indicate that the E. coli nar promoter system can be used as an oxygen-dependent inducible promoter in both Agrobacterium and Pseudomonas host strains.

Titanium dioxide (TiO2) nanoparticles were decorated with different amounts of silver nanoparticles (AgNPs) using an electrochemically active biofilm (EAB), which is a biogenic approach that leads to the formation of Ag@TiO2 nanocomposites. UV-vis spectroscopy, photoluminescence, X-ray diffraction and electron microscopy showed AgNPs, 2–5 nm in size, well-dispersed and anchored to the TiO2 surface and overall synthesis of Ag@TiO2 nanocomposites. The photocatalytic performance of the as-synthesized Ag@TiO2 nanocomposites was evaluated in terms of their efficiency for the photodecomposition of methylene blue (MB) in an aqueous solution under visible light irradiation. The nanocomposites showed exceptionally high photodecomposition efficiency (>7 times) compared to commercial TiO2 (Sigma). The enhanced photocatalytic activity was attributed to the synergistic contribution of both a delayed charge recombination rate caused by the high electronic mobility of the AgNPs and the increased surface area originating from the nanometer sized AgNPs on TiO2. The nanocomposites also showed exceptionally high stability and reusability under similar experimental conditions.

Band gap narrowing is important and advantageous for potential visible light photocatalytic applications involving metal oxide nanostructures. This paper reports a simple biogenic approach for the promotion of oxygen vacancies in pure zinc oxide (p-ZnO) nanostructures using an electrochemically active biofilm (EAB), which is different from traditional techniques for narrowing the band gap of nanomaterials. The novel protocol improved the visible photocatalytic activity of modified ZnO (m-ZnO) nanostructures through the promotion of oxygen vacancies, which resulted in band gap narrowing of the ZnO nanostructure (Eg = 3.05 eV) without dopants. X-ray diffraction, UV-visible diffuse reflectance spectroscopy, X-ray photoelectron spectroscopy, electron paramagnetic resonance spectroscopy, Raman spectroscopy, photoluminescence spectroscopy and high resolution transmission electron microscopy confirmed the oxygen vacancy and band gap narrowing of m-ZnO. m-ZnO enhanced the visible light catalytic activity for the degradation of different classes of dyes and 4-nitrophenol compared to p-ZnO, which confirmed the band gap narrowing because of oxygen defects. This study shed light on the modification of metal oxide nanostructures by EAB with a controlled band structure.

Background Bacteria use diverse signaling molecules to ensure the survival of the species in environmental niches. A variety of both Gram-positive and Gram-negative bacteria produce large quantities of indole that functions as an intercellular signal controlling diverse aspects of bacterial physiology. Results In this study, we sought a novel role of indole in a Gram-positive bacteria Paenibacillus alvei that can produce extracellular indole at a concentration of up to 300 μM in the stationary phase in Luria-Bertani medium. Unlike previous studies, our data show that the production of indole in P. alvei is strictly controlled by catabolite repression since the addition of glucose and glycerol completely turns off the indole production. The addition of exogenous indole markedly inhibits the heat resistance of P. alvei without affecting cell growth. Observation of cell morphology with electron microscopy shows that indole inhibits the development of spore coats and cortex in P. alvei. As a result of the immature spore formation of P. alvei, indole also decreases P. alvei survival when exposed to antibiotics, low pH, and ethanol. Additionally, indole derivatives also influence the heat resistance; for example, a plant auxin, 3-indolylacetonitrile dramatically (2900-fold) decreased the heat resistance of P. alvei, while another auxin 3-indoleacetic acid had a less significant influence on the heat resistance of P. alvei. Conclusions Together, our results demonstrate that indole and plant auxin 3-indolylacetonitrile inhibit spore maturation of P. alvei and that 3-indolylacetonitrile presents an opportunity for the control of heat and antimicrobial resistant spores of Gram-positive bacteria.

Silver nanoparticles 1–7 nm in size were synthesized within 2 h in water by challenging an electrochemically active biofilm (EAB) with a solution containing AgNO3 as precursor and sodium acetate as an electron donor. The electrochemically active bacteria present on the anaerobic biofilm act as a catalyst to oxidise the sodium acetate by producing electrons for the reduction of Ag+ ions. The high monodispersity, rapidity, and extracellular nature of this synthesis, together with the production of smaller nanoparticles that are easily separated, make this protocol highly significant in the area of nanoparticle synthesis.

In order to increase the oxygen transfer in a bioreactor for Hybridoma cell culture, a perfluorocarbon, FlutecR ppll was used in a modified CelligenTM system. There was no harmful effect of ppll on the cell growth and on the production of monoclonal antibody.

Removal of SO2 gas from simulated flue gases was carried out, using copper oxide adsorbent. The copper oxide absorbent is made by impregnation of γ-alumina tablet in a solution of copper (II) nitrate, followed by oxidation. SO2 breakthrough curves were obtained by changing temperature and initial concentration in a tubular packed bed reactor. The kinetic parameters were determined by fitting breakthrough curves to the theoretical kinetic model, and the rate equation was obtained. The saturation capacities were calculated by the numerical integration of breakthrough curves, and the equation representing breakthrough curves was obtained. By means of this equation, the influence of space time on breakthrough curves was estimated.