Applied Microbiology and Biotechnology

Correction to: Genetically engineered probiotic Saccharomyces cerevisiae strains mature human dendritic cells and stimulate gag-specific memory CD8 + T cells ex vivo In the Funding section, the following statement is missing: The MACS cohort study was supported by the NIH, National Institute of Allergy and Infectious Diseases grant U01-AI35041.

Correction to: Glycerol metabolism and its regulation in lactic acid bacteria The original publication of this paper contains some errors.

Correction to: Phloretin reduces cell injury and inflammation mediated by Staphylococcus aureus via targeting sortase B and the molecular mechanism The images of cells under microscope in Figure 2 and Figure S2 were misused from Wang G et al. Front Cell Infect Microbiol. 2018 Nov 30;8:418. These images were generated in the same set of assays.

Biofilm reactors as a promising method for vitamin K (menaquinone-7) production Abstract Menaquinone-7 (MK-7) is the most potent subtype of vitamin K with extraordinarily high half-life in the circulatory system. Therefore, MK-7 plays a critical role in promoting human wellbeing today. Studies on MK-7 every year show more and more magnificent benefits of it in preventing cardiovascular diseases and osteoporosis to battling cancer cells, Alzheimer's and Parkinson's diseases. Thus, it needs to be supplemented to daily diet for accumulative and long-term benefits. Chemical synthesis of MK-7 produces a significant cis-isomer form of it, which has no biological activity. Fortunately, due to its key role in electron transfer in bacteria, trans-MK-7 is biosynthesized by especially Gram-positive strains mainly Bacillus genus. Concordantly, MK-7 could be produced via solid or liquid state fermentation strategies. In either regime, when static fermentation is applied in the absence of agitation and aeration, operational issues arise such as heat and mass transfer inefficiencies. Thus, scaling up the process becomes a challenge. On the other hand, studies have indicated that biofilm and pellicle formation that occur in static fermentations are key characteristics for extracellular MK-7 secretion. Therefore, this review covers the most recent discoveries of the therapeutic properties of MK-7 and optimization attempts at increasing its biosynthesis in different media compositions and effective growth parameters as well as the cutting-edge use of biofilm reactors where B. subtilis cells have the infrastructures to form mature biofilm formations on plastic composite supports. Biofilm reactors therefore can provide robust extracellular MK-7 secretion while simultaneously enduring high agitation and aeration rates, which then address the scale-up and operational issues associated with static fermentation strategies.

Co-culture of Lactobacillus delbrueckii and engineered Lactococcus lactis enhances stoichiometric yield of d -lactic acid from whey permeate Abstract d-Lactic acid (d-LA) is an enantiomer of lactic acid, which has a niche application in synthesis of poly-lactic acid based (PLA) polymer owing to its contribution to the thermo-stability of stereo-complex PLA polymer. Utilization of renewable substrates such as whey permeate is pivotal to economically viable production of d-LA. In present work, we have demonstrated d-LA production from whey permeate by Lactobacillus delbrueckii and engineered Lactococcus lactis. We observed that lactose fermentation by a monoculture of L. delbrueckii yields d-LA and galactose as major products. The highest yield of d-LA obtained was 0.48 g g−1 when initial lactose concentration was 30 g L−1. Initial lactose concentration beyond 20 g L−1 resulted in accumulation of glucose and galactose, and hence, reduced the stoichiometric yield of d-LA. L. lactis naturally produces l-lactic acid (l-LA), so a mutant strain of L. lactis (L. lactis Δldh ΔldhB ΔldhX) was used to prevent l-LA production and engineer it for d-LA production. Heterologous over-expression of d-lactate dehydrogenase (ldhA) in the recombinant strain L. lactis TSG1 resulted in 0.67 g g−1 and 0.44 g g−1 of d-LA yield from lactose and galactose, respectively. Co-expression of galactose permease (galP) and α-phosphoglucomutase (pgmA) with ldhA in the recombinant strain L. lactis TSG3 achieved a d-LA yield of 0.92 g g−1 from galactose. A co-culture batch process of L. delbrueckii and L. lactis TSG3 achieved an enhanced stoichiometric yield of 0.90 g g−1 and ~45 g L−1d-LA from whey permeate (lactose). This is the highest reported yield of d-LA from lactose substrate, and the titres can be improved further by a suitably designed fed-batch co-culture process.

Biological agents for 2,4-dichlorophenoxyacetic acid herbicide degradation Abstract Phenoxy herbicides are the most widely used family of herbicides worldwide. The dichlorophenoxyacetic acid (2,4-D) is extensively used as a weed killer on cereal crops and pastures. This herbicide is highly water-soluble, and even after a long period of disuse, considerable amounts of both 2,4-D and its main product of degradation, 2,4 dichlorophenol (2,4-DCP), might be found in nature. Biological decomposition of pesticides is an expressive and effective way for the removal of these compounds from the environment. The role of bacteria as well as the enzymes and genes that regulate the 2,4-D degradation has been widely studied, but the 2,4-D degradation by fungi, especially regarding the ability of white-rot basidiomycetes as agent for its bioconversion, has been not extensively considered. This review discusses the current knowledge about the biochemical mechanisms of 2,4-D biodegradation, focused on the role of white-rot fungi in this process. Finally, the cultivation conditions and medium composition for the growth of 2,4-D-degrading microorganisms are also addressed.

Highly regio- and enantioselective synthesis of chiral intermediate for pregabalin using one-pot bienzymatic cascade of nitrilase and amidase Abstract Nitrilase-mediated hydrolysis of isobutylsuccinonitrile (IBSN) is a highly attractive approach for (S)-3-cyano-5-methylhexanoic acid ((S)-CMHA), the critical chiral intermediate of pregabalin. In this study, a robust nitrilase from Arabis alpina (AaNIT) was screened and engineered. The N258D mutant was obtained with high catalytic activity and excellent enantioselectivity (E > 300) towards IBSN at a high substrate concentration of 100 g L−1. Byproduct (S)-3-cyano-5-methyl hexanoic amide ((S)-CMHM) was detected and identified for the first time during the catalytic process. By employing a feasible one-pot bienzymatic cascade of mutant N258D and amidase from Pantoea sp. (Pa-Ami) expressed separately in recombinant Escherichia coli cells, the byproduct (S)-CMHM was eliminated and (S)-CMHA was obtained with a conversion of 45.0% and eep of 99.3%. These results provided the novel plant-derived nitrilase as a promising biocatalyst for (S)-CMHA biosynthesis and demonstrated the feasibility of one-pot bienzymatic cascade reaction for large-scale production of the pregabalin precursor.

YKL107W from Saccharomyces cerevisiae encodes a novel aldehyde reductase for detoxification of acetaldehyde, glycolaldehyde, and furfural Abstract The aldehyde reductases from the short-chain dehydrogenase/reductase (SDR) family were identified as a series of critical enzymes for the improved tolerance of Saccharomyces cerevisiae to the aldehydes by catalyzing the detoxification reactions of aldehydes. Herein, we report that a novel aldehyde reductase Ykl107wp deduced from YKL107W from S. cerevisiae belongs to the classical SDR group and can catalyze the reduction reactions of acetaldehyde (AA), glycolaldehyde (GA), furfural (FF), formaldehyde (FA), and propionaldehyde (PA) but cannot reduce the six representative ketones. Ykl107wp displayed the best maximum velocity (Vmax), catalytic rate constant (Kcat), catalytic efficiency (Kcat/Km), and highest affinity (Km) to acetaldehyde. The optimum pH of Ykl107wp was 6.0 for the reduction of AA and 7.0 for the reduction of GA and FF, and the optimum temperatures were 40, 35, and 30 °C for the reduction of AA, GA, and FF, respectively. Ykl107wp for the reduction of AA was greatly affected by metal ions, chemical additives, and salts and showed poor thermal and pH stability, but its stability was slightly affected by a substrate. Ykl107wp was localized in endoplasmic reticulum and prevented the yeast cells from damage caused by furfural via the detoxification of furfural to furfural alcohol. This research provides guidelines for the study of uncharacterized classical SDR aldehyde reductases and exploration of their protective mechanisms on the corresponding organelles.

Structural modulation of gut microbiota reveals Coix seed contributes to weight loss in mice Abstract Coix seed (CS) is widely used as food material and herbal medicine in Asian countries with hypolipidemic and anti-inflammatory properties. But whether CS takes effect by modulating the composition of the gut microbiota remains unknown. Here, three groups of mice were fed different diets for 5 weeks: standard chow, high fat (HF), and CS added to HF. As compared to chow, mice in HF group demonstrated a significant increase in body weight (BW), fat mass (FM), together with total cholesterol (TC), and they even developed impaired glucose tolerance. These HF-mediated deleterious metabolic effects were counteracted partly by complementing CS. 16S rRNA gene sequencing analysis revealed CS increased the abundance of genera Lactobacillus, Coprococcus, and Akkermansia in the gut microbita, and it also enriched species Akkermansia muciniphila and Lactobacillus agilis. A. muciniphila was reported to be inversely associated with obesity, diabetes and cardiometabolic diseases, while L. agilis was negatively associated with TC, BW, FM and blood glucose in our data. We identified CS-altered microbial metabolic pathways that were linked to Glycerolipid metabolism, Biosynthesis of unsaturated fatty acids, sulfur reduction, and glutathione transport system. Our results indicate CS may be used as prebiotic agents to lose weight and prevent obesity-related metabolic disorders.

Protein expression analysis revealed a fine-tuned mechanism of in situ detoxification pathway for the tolerant industrial yeast Saccharomyces cerevisiae Abstract Inhibitory compounds liberated from lignocellulose pretreatment are representative toxic chemicals that repress microbial growth and metabolism. A tolerant strain of the industrial yeast Saccharomyces cerevisiae is able to detoxify a major class of toxic compounds while producing ethanol. Knowledge on the yeast tolerance was mostly obtained by gene expression analysis and limited protein expression evidence is yet available underlying the yeast adaptation. Here we report a comparative protein expression profiling study on Y-50049, a tolerant strain compared with its parental industrial type strain Y-12632. We found a distinctive protein expression of glucose-6-phosphate dehydrogenase (Zwf1) in Y-50049 but not in Y-12632, in the relatively conserved glycolysis and pentose phosphate pathway (PPP) in response to a combinational challenge of 2-furaldehyde (furfural) and 5-hydroxymethyl-2-furaldehyde (HMF). A group of proteins with aldehyde reduction activity was uniquely induced expressed in Y-50049 but not in Y-12632. Such evidence allowed fine-tuning a mechanism of the renovated in situ detoxification by Y-50049. As the key protein, Zwf1 drove the glucose metabolism in favor of the oxidative branch of the PPP facilitating in situ detoxification of the toxic chemicals by Y-50049. The activated expression of Zwf1 generated the essential cofactor nicotinamide adenine dinucleotide phosphate (NADPH) enabling reduction of furfural and HMF through a group of aldehyde reduction enzymes. In return, the activate aldehyde reductions released desirable feedbacks of NADP+ stimulating continued oxidative activity of Zwf1. Thus, a well-maintained cofactor regeneration cycle was established to restore the cofactor imbalance caused by furfural-HMF. Challenges and perspectives on adaptation of significantly differential expressions of ribosomal proteins and other unique proteins are also discussed.

Alexandros Sfakianakis
Anapafseos 5 . Agios Nikolaos
Crete.Greece.72100
2841026182

6948891480

alsfakia@gmail.com