Enhanced chaotrope tolerance and (S)-2-hydroxypropiophenone production by recombinant Pseudomonas putida engineered with Pprl from Deinococcus radiodurans

Pseudomonas putida is a soil bacterium with multiple uses in fermentation and biotransformation processes. P. putida ATCC 12633 can biotransform benzaldehyde and other aldehydes into valuable α-hydroxyketones, such as (S)-2-hydroxypropiophenone. However, poor tolerance of this strain toward chaotropic aldehydes hampers efficient biotransformation processes. To circumvent this problem, we expressed the gene encoding the global regulator PprI from Deinococcus radiodurans, an inducer of pleiotropic proteins promoting DNA repair, in P. putida. Fine-tuned gene expression was achieved using an expression plasmid under the control of the LacIQ /Ptrc system, and the cross-protective role of PprI was assessed against multiple stress treatments. Moreover, the stress-tolerant P. putida strain was tested for 2-hydroxypropiophenone production using whole resting cells in the presence of relevant aldehyde substrates. P. putida cells harbouring the global transcriptional regulator exhibited high tolerance toward benzaldehyde, acetaldehyde, ethanol, butanol, NaCl, H2 O2 and thermal stress, thereby reflecting the multistress protection profile conferred by PprI. Additionally, the engineered cells converted aldehydes to 2-hydroxypropiophenone more efficiently than the parental P. putida strain. 2-Hydroxypropiophenone concentration reached 1.6 g L-1 upon a 3-h incubation under optimized conditions, at a cell concentration of 0.033 g wet cell weight mL-1 in the presence of 20 mM benzaldehyde and 600 mM acetaldehyde. Product yield and productivity were 0.74 g 2-HPP g-1 benzaldehyde and 0.089 g 2-HPP g cell dry weight-1  h-1 , respectively, 35% higher than the control experiments. Taken together, these results demonstrate that introducing PprI from D. radiodurans enhances chaotrope tolerance and 2-HPP production in P. putida ATCC 12633.

Optimized enantioselective (S)-2-hydroxypropiophenone synthesis by free- and encapsulated-resting cells of Pseudomonas putida

BACKGROUND

Aromatic α-hydroxy ketones, such as S-2-hydroxypropiophenone (2-HPP), are highly valuable chiral building blocks useful for the synthesis of various pharmaceuticals and natural products. In the present study, enantioselective synthesis of 2-HPP was investigated by free and immobilized whole cells of Pseudomonas putida ATCC 12633 starting from readily-available aldehyde substrates. Whole resting cells of P. putida, previously grown in a culture medium containing ammonium mandelate, are a source of native benzoylformate decarboxylase (BFD) activity. BFD produced by induced P. putida resting cells is a highly active biocatalyst without any further treatment in comparison with partially purified enzyme preparations. These cells can convert benzaldehyde and acetaldehyde into the acyloin compound 2-HPP by BFD-catalyzed enantioselective cross-coupling reaction.

RESULTS

The reaction was carried out in the presence of exogenous benzaldehyde (20 mM) and acetaldehyde (600 mM) as substrates in 6 mL of 200 mM phosphate buffer (pH 7) for 3 h. The optimal biomass concentration was assessed to be 0.006 g dry cell weight (DCW) mL^- 1. 2-HPP titer, yield and productivity using the free cells were 1.2 g L^- 1, 0.56 g 2-HPP/g benzaldehyde (0.4 mol 2-HPP/mol benzaldehyde), 0.067 g 2-HPP g^- 1 DCW h^- 1, respectively, under optimized biotransformation conditions (30 °C, 200 rpm). Calcium alginate (CA)-polyvinyl alcohol (PVA)-boric acid (BA)-beads were used for cell entrapment. Encapsulated whole-cells were successfully employed in four consecutive cycles for 2-HPP production under aerobic conditions without any noticeable beads degradation. Moreover, there was no production of benzyl alcohol as an unwanted by-product.

CONCLUSIONS

Bioconversion by whole P. putida resting cells is an efficient strategy for the production of 2-HPP and other α-hydroxyketones.

Application of a membrane-less air cathode microbial fuel cell to treat municipal waste composting leachate

The adverse effects of high strength wastewaters on the microbial activities have created a challenge to biological treatments. Microbial fuel cell has been considered as a promising process because the electrical potential generation can stimulate microorganisms and overcome the inhibitory effect. However, several issues (e.g., scalability, high costs and maintenance) have prevented the process from the industrial applications. Elimination of the proton exchange membrane has been suggested as a remedy to the mentioned problems. In this work, a membrane-less microbial fuel cell was modified by putting the cathode within a thin sand layer (instead of the proton exchange membrane) to treat a high strength wastewater sample. The influences of the feed organic load and time of treatment in the modified system were studied in batch and continuous operations. It was revealed that the batch operation efficiency was higher for the lower feed loadings as a 5-day batch treatment removed 66 ± 4% of the 15,000 ± 500 mg/L initial chemical oxygen demand while the continuous process efficiency with 9-day hydraulic residence time was slightly more than 50%. However, the efficiency of the continuous operation for treatment of higher initial loading values was better than the batch mode with the removal efficiency of 41 ± 2% versus 12 ± 2% for a more concentrated leachate feed (45,000 ± 1000 mg/L). Finally, it was disclosed that the modified membrane-less MFC employed in this work can be effective in treatment of high strength wastewaters in larger scales with lower costs.

Tailored lipopeptide surfactants as potentially effective drugs to treat SARS-CoV-2 infection

Finding effective drugs to treat SARS-CoV-2 infection as a complementary step to the extensive vaccination is of the great importance to overcome the current pandemic situation. It has been shown that some bio-active unsaturated fatty acids such as Arachidonic Acid (AA) can reduce the infection severity and even destroy the virus by disintegration of the virus lipid envelope. On the other hand, it has been reported that several designed peptides with an activity similar to the angiotensin converting enzyme 2 (ACE-2), which has a high affinity towards the novel corona virus spike protein, can inhibit the viral infection through concealing the spike proteins from the cell surfaces ACE-2. Binding the mentioned peptides to the bio-active lipids like AA will result in a lipopeptide surfactant molecule with the synergistic effect of both the active moieties in its structure to treat the novel corona infection. In addition, the peptide segment increases the aqueous solubility of the lipid segment and enables the targeted delivery of the surfactant molecule to the virus. The resultant lipopeptide would be a potentially effective drug for SARS-CoV-2 infection treatment with the minimum side effects.

The promiscuous potential of cellulase in degradation of polylactic acid and its jute composite

It has been suggested that cellulolytic enzymes can be effective on the degradation of PLA samples. The idea was investigated by examining the impact of cellulase on degradation of PLA and PLA-jute (64/36) composite in an aqueous medium. The obtained results demonstrated 55% and 61% thickness reduction in PLA and PLA-jute specimens after four months of treatment, respectively. Gel permeation chromatography (GPC) showed significant decline in the number average molecular weight (M_n) approximately equal to 85% and 80% for PLA and PLA-jute in comparison with their control. The poly dispersity index (PDI) of PLA and PLA-jute declined 41% and 49% that disclosed more homogenous distribution in molecular weight of the polymer after treatment with cellulase. The cellulase promiscuity effect on PLA degradation was further revealed by Fourier-transform infrared spectroscopy (FT-IR) analysis where substantial decrease in the peak intensities of the polymer related functional groups were observed. In addition, PLA biodegradation was studied in more detail by differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA) of control and cellulase treated specimens. The obtained results confirmed the promiscuous function of cellulase in the presence or the absence of jute as the specific substrate of cellulase. This can be considered as a major breakthrough to develop effective biodegradation processes for PLA products at the end of their life cycle.

Investigation of the Role of Glucose Decorated Chitosan and PLGA Nanoparticles as Blocking Agents to Glucose Transporters of Tumor Cells

PURPOSE

Glucose decorated PLGA and chitosan nanoparticles (GPNPs and GCNPs) have been developed to examine the possibility of preventing the facilitated glucose transport to the cells through blocking the glucose transporters (Gluts) overexpressed by tumor cells.

METHODS

The MTT assay was used to assess the cytotoxicity towards human colon tumor (HT-29) cells in 72 hrs. Fluorescence microscopy was employed to confirm the attachment of GPNPs to the cells. Moreover, the GPNPs effects on the apoptotic rate of HT-29 cells were analyzed. Finally, the expression levels of GLUT-1 and GLUT-4 by real-time polymerase chain reaction (RT-PCR) were assayed to investigate the response of HT-29 cells to blocking their Gluts by GPNPs.

RESULTS

The stability studies showed that the synthesized complexes were mostly stable (more than 80%) at various temperatures (4 to 40ºC) and pH (5.4 to 7.4) conditions. Results indicated that the survival rate of the cells was decreased to 43% and 46% after treatment with GCNPs and GPNPs, respectively. Also, the apoptosis assay results showed that the percentage of viable cells reduced to 47% after GPNPs treatment. These observations were justified by the specific interactions between the glucose terminals and the cells Gluts which resulted in blocking the entries of nutrients to the cells. It was revealed that the GLUT-1 mRNA expression after the first 24 h of treatment by GPNPs was upregulated to more than 145%, while the direction was reversed after 72 h (expression less than 45%), which coincided with the cells death. In the first 24 h, the glucose deprivation stimulated the expression of Glut-1 while the apoptotic enzymes expression was dominant at the end of 72 h treatment time.

CONCLUSION

Finally, it can be concluded that the glucose-nanoparticle complexes could be considered as promising agents in cancer therapy.

Treatment of normal hydrocarbons contaminated water by combined microalgae - Photocatalytic nanoparticles system

Two species of microalgae (Chlorella vulgaris and Dunaliella tertiolecta) as the biological agents along with ZnO nanoparticles as the photocatalyst were used to investigate the hydrocarbon removal efficiency from oily water samples. Firstly, the toxicities of the photocatalyst, normal paraffine hydrocarbons and their combination towards the microalgae were evaluated in terms of cell growth and chlorophyll content. The capability of algae to absorb the nanoparticles in the aqueous phase was confirmed by FT-IR spectroscopy. Then, the hydrocarbon removal efficiencies of the algae, photocatalyst and the combined photocatalyst-algae system were studied by measuring the residual hydrocarbon content of the samples. Results indicated that despite of the growth inhibitory effects of n-alkanes and nanoparticles on the examined algae, both of them could survive in the system. Dunaliella tertiolecta was more affected by normal paraffins while Chlorella vulgaris was more sensitive to ZnO nanoparticles. Both of the studied species were capable of hydrocarbon removal and the efficiency of Chlorella vulgaris was superior. The combination of algae and nanoparticles was also proved to have a synergistic effect on degradation of the hydrocarbon content of the medium. The obtained removal efficiencies for initial hydrocarbon concentrations of 0.05%, 0.1% and 0.5% (v/v) were 100%, 78% and 42% for Dunaliella tertiolecta-ZnO and 100%, 93% and 88% for Chlorella vulgaris- ZnO system, respectively. It can be concluded that the examined microalgae-nanoparticle system can be considered as a final polishing step in hydrocarbons removal from oily waters.

Investigation of platinum recovery from a spent refinery catalyst with a hybrid of oxalic acid produced by Aspergillus niger and mineral acids

The capability of oxalic acid produced by Aspergillus niger was investigated for bioleaching of platinum from a refinery reforming catalyst. The spent medium mode was selected for bioleaching because of its higher efficiency at favorable pH and temperature conditions. The effects of several important factors such as the pulp density, pH and temperature on platinum recovery were optimized using Box-Behnken design of response surface methodology. The results indicated that pH adjustment during the bioleaching process increases the final platinum recovery significantly. The obtained optimum conditions were 1% for the pulp density, 0.5 for the medium pH, and 70 °C for the temperature which led to 37% platinum recovery. The significance of oxalic acid as the leaching agent in platinum bioleaching was highlighted by investigating the recovery of a blank medium without oxalic acid at the optimum conditions which was just about 13%. The presented method can be utilized in an environmentally friendly process to recover platinum from industrial catalysts.

The synergetic effect of starch and alpha amylase on the biodegradation of n-alkanes

The impact of adding soluble starch on biodegradation of n-alkanes (C10-C14) by Bacillus subtilis TB1 was investigated. Gas chromatography was employed to measure the residual hydrocarbons in the system. It was observed that the efficiency of biodegradation improved with the presence of starch and the obtained residual hydrocarbons in the system were 53% less than the samples without starch. The produced bacterial enzymes were studied through electrophoresis and reverse zymography for explaining the observations. The results indicated that the produced amylase by the bacteria can degrade hydrocarbons and the same was obtained by the application of a commercial alpha amylase sample. In addition, in silico docking of alpha-amylase with n-alkanes with different molecular weights was studied by Molegro virtual docker which showed high negative binding energies and further substantiated the experimental observations. Overall, the findings confirmed the catalytic effect of alpha amylase on n-alkanes degradation.

Modelling bio-electrosynthesis in a reverse microbial fuel cell to produce acetate from CO2and H2O

Bio-electrosynthesis of organic compounds (citrate) in a reverse microbial fuel cell.