Microbial calcium carbonate precipitation with high affinity to fill the concrete pore space: nanobiotechnological approach

Bioprocess and Biosystems Engineering - Despite the advantages of concrete, it has a pore structure and is susceptible to cracking. The initiated cracks as well as pores and their connectivity...     

Optimization of Bacillus subtilis natto growth parameters in glycerol-based medium for vitamin K (Menaquinone-7) production in biofilm reactors

Bioprocess and Biosystems Engineering - Menaquinone-7 (MK-7) is the key form of vitamin K used as a dietary supplement and its production revolves around Bacillus subtilis natto. Current...     

Implementation of fed-batch strategies for vitamin K (menaquinone-7) production by Bacillus subtilis natto in biofilm reactors

Recent studies show the essential health benefits associated with vitamin K, especially menaquinone-7 (MK-7). These benefits include reducing risks of cardiovascular diseases, osteoporosis, and even cancer. However, MK-7 production on an industrial level is only possible through bacterial fermentation and also current static fermentation strategies are not potent enough with difficulties to scale up. Biofilm reactors, however, may be a practical alternative. Biofilm reactors provide a controlled environment for the microorganisms to form mature and robust biofilms that enable them to produce value-added products with enhanced efficiencies. In this study, fed-batch addition of glucose and glycerol were investigated to the base media in biofilm reactors, as carbon source addition seemed crucial in batch fermentations. Results indicated that fed-batch strategies can be significantly effective in glucose-based medium, increasing the end-product concentrations to 28.7 ± 0.3 mg/L of MK-7 which was 2.3 fold higher than the level produced in suspended-cell bioreactors and renders the biofilm reactors as a potential replacement for static fermentation strategies. Moreover, morphological changes of B. subtilis were tracked during the 12-day long fermentation runs and finally, SEM investigations confirmed significant biofilm and extracellular matrices formed on the plastic composite support (PCS) in the biofilm reactors. In conclusion, biofilm reactors especially with fed-batch fermentation regimes seem to be an effective tool for MK-7 production at industrial scales.

     

Correction to: Effect of Chromium Nanoparticles on Physiological Stress Induced by Exogenous Dexamethasone in Japanese Quails

Biological Trace Element Research - Chromium (Cr), as an essential trace element, plays a critical role in carbohydrate, protein, and lipid metabolism in animals. It has been suggested that the...     

Suppression of RNA interference by adenovirus virus-associated RNA

We show that human adenovirus inhibits RNA interference (RNAi) at late times of infection by suppressing the activity of two key enzyme systems involved, Dicer and RNA-induced silencing complex (RISC). To define the mechanisms by which adenovirus blocks RNAi, we used a panel of mutant adenoviruses defective in virus-associated (VA) RNA expression. The results show that the virus-associated RNAs, VA RNAI and VA RNAII, function as suppressors of RNAi by interfering with the activity of Dicer. The VA RNAs bind Dicer and function as competitive substrates squelching Dicer. Further, we show that VA RNAI and VA RNAII are processed by Dicer, both in vitro and during a lytic infection, and that the resulting short interfering RNAs (siRNAs) are incorporated into active RISC. Dicer cleaves the terminal stem of both VA RNAI and VA RNAII. However, whereas both strands of the VA RNAI-specific siRNA are incorporated into RISC, the 3' strand of the VA RNAII-specific siRNA is selectively incorporated during a lytic infection. In summary, our work shows that adenovirus suppresses RNAi during a lytic infection and gives insight into the mechanisms of RNAi suppression by VA RNA.     

Mechanical properties of bio self-healing concrete containing immobilized bacteria with iron oxide nanoparticles

Applied Microbiology and Biotechnology - Concrete is arguably one of the most important and widely used materials in the world, responsible for the majority of the industrial revolution due to its...     

Influence of Small RNAs on Biofilm Formation Process in Bacteria

Small non-coding RNAs (sRNAs) play a significant role in regulation of bacterial physiological behaviors. After sensing any environmental cue such as fluctuation of nutrient concentration, temperature, pH, and osmolarity, these sRNAs interfere to transmit these signals to target regulators and genes. sRNAs have key role in biofilm formation process by base pairing with target mRNAs or interaction with modulating proteins to both positive and negative regulation mechanisms. There are various regulatory systems to characterize the initiation and formation of special bacterial biofilms that are mostly described as two component systems based on sRNAs functions. In this study, regulatory pathways that are important for biofilm formation and genetic responses to environmental stimuli in mature biofilms were evaluated. Some of the regulatory systems that produce common types of biofilms such as curli, PGA, cellulose and polysaccharides such as alginate, colonic acid, Psl and their involved sRNAs functions were also discussed.     

Effect of Biofilm Formation by Bacillus subtilis natto on Menaquinone-7 Biosynthesis

Bacillus subtilis natto is the key microorganism for the industrial production of menaquinone-7. The fermentation of this bacterium in static culture is associated with biofilm formation. The objective of this study was to determine the effect of biofilm formation on menaquinone-7 production to develop a suitable bio-reactor for the production of menaquinone-7. In the static culture, menaquinone-7 biosynthesis showed a linear correlation with biofilm formation (R ² = 0.67) and cell density (R ² = 0.7). The amount of biofilm, cell density and menaquinone-7 formation were a function of nutrient and processing conditions. Glycerol, soy peptone, and yeast extract mixture and 40 °C were found to be the optimum nutrients and temperature for accelerating both biofilm and menaquinone-7 biosynthesis in static culture. However, glucose, mixture of soy peptone and yeast extract and 45 °C were found to be the optima for cell density. As compared to the static culture, the biofilm formation was significantly inhibited when a shaken fermentation was used. However, shaking caused only a small decrease on menaquinone-7 production. These results demonstrate that the biofilm formation is not essential for menaquinone-7 biosynthesis. This study underlines the feasibility of using large scale stirred fermentation process for menaquinone-7 production.