Rate Of Acid Production Research Articles

The YvqE two-component system controls biofilm formation and acid production in Streptococcus pyogenes.

In Streptococcus pyogenes, proteins involved in determining virulence are controlled by stand-alone response regulators and by two-component regulatory systems. Previous studies reported that, compared to the parental strain, the yvqE sensor knockout strain showed significantly reduced growth and lower virulence. To determine the function of YvqE, we performed biofilm analysis and pH assays on yvqE mutants, and site-directed mutagenesis of YvqE. The yvqE deletion mutant showed a slower acid production rate, indicating that YvqE regulates acid production from sugar fermentation. The mutant strain, in which the Asp(26) residue in YvqE was replaced with Asn, affected biofilm formation, suggesting that this amino acid senses hydrogen ions produced by fermentative sugar metabolism. Signals received by YvqE were directly or indirectly responsible for inducing pilus expression. This study shows that at low environmental pH, biofilm formation in S. pyogenes is mediated by YvqE and suggests that regulation of pilus expression by environmental acidification could be directly under the control of YvqE.

Effect of Electrical Stimulation on Grasshopper Jumping Muscle

Skeletal muscles can undergo biochemical and physiological changes due to exercise training. For example, aerobic exercise training may lead to an increased mitochondria volume, a higher proportion of slow twitch myosin ATPase, and a reduced rate of lactic acid production. Similar changes in mammalian muscle have also been demonstrated using electrical stimulation. However, it is unclear if invertebrate muscle also responds to training or electrical stimulation. We examine whether Schistocerca americana grasshopper jumping muscles are affected by electrical stimulation. Grasshopper jumping muscle is one of the few invertebrate muscles to produce lactic acid during locomotion. Electrical probe leads are placed near the coxa on the ventral side of the animal. The muscle was stimulated with a single pulse width of 2 ms at 0.075 V and repeated at a frequency of 100 Hz. We electrically stimulate the entire jumping muscle, including both the flexor and the extensor, to elicit continuous muscle contractions in a single metathoracic leg. To invoke a training response, a grasshopper is stimulated for 5 hours daily for 5 consecutive days. The lactate production rate of trained and untrained grasshopper muscle will then be fluorometrically measured after 5 min, 30 min, 60 min, 180 min, or 300 min of electrical stimulation. We predict that repeated stimulation would alter the rate of lactic acid production. Since grasshopper jumping muscle is similar to human muscle, this research may provide insight into fundamental questions about muscle plasticity.Support or Funding InformationUnion College Undergraduate Research Committee

Long-term anti-cariogenic biofilm activity of glass ionomers related to fluoride release

ObjectivesThe aim of this study was to evaluate the difference between anti-cariogenic biofilm activities of glass ionomers (G-Is) during the initial and second fluoride release phases and to define relationships between the anti-biofilm activities and fluoride release. MethodsFluoride release of three commercially available G-Is in a buffer was evaluated for 770h, and then 70-h-old Streptococcus mutans UA159 biofilms were formed on the G-Is that had been immersed in the buffer for 0, 100, 200, or 700h. The dry weight, bacterial cell number, water-insoluble extracellular polysaccharides (EPSs), and accumulated fluoride concentration of the 70-h-old biofilms and fluoride release and acid production rates during biofilm formation were determined. Relationships between the experimental variables and fluoride release rate were also evaluated using linear regression analysis. ResultsIn this study, fluoride release of the tested G-Is did not exhibit a biphasic pattern during biofilm formation. The release was sustained or did not rapidly decrease even over long immersion periods and was strongly correlated with an increase in accumulated fluoride concentration of the biofilms (R=0.99, R2=0.98) and reductions in dry weight, water-insoluble EPSs, and acid production rate of the biofilms (R=−0.99 to −0.96, R2=0.92–0.98). ConclusionsThis study suggests that G-Is can effectively affect acid production, EPS formation, and accumulation of cariogenic biofilms even during the second fluoride release phase, and that the anti-cariogenic biofilm activity is strongly correlated with fluoride release, which may be enhanced by acid production of cariogenic biofilms. Clinical significanceG-Is can affect cariogenic biofilm formation even during the second fluoride release phase.

Relationship between Sowing Time, Variety, and Quality in Safflower

This research was carried out to determine the rates of protein and oil production and fatty acid composition and their correlation coefficients in four safflower cultivars (Remzibey, Dincer, Balci, and Yenice) sown in the autumn and spring from 2013 to 2015. The experiment was carried out using split plots in a randomized block design and was replicated 3 times. The study found protein production rates between 15.20 and 18.08%, oil production rates between 24.58 and 31.99%, palmitic acid production rates between 5.93 and 7.01%, stearic acid production rates between 2.13 and 2.53%, oleic acid production rates between 12.08 and 31.58%, linoleic acid production rates between 78.61 and 59.08%, and linolenic acid production rates between 0.11 and 0.15%. Higher seed oil content values were obtained from spring sowing compared to autumn sowing (27.42% and 26.10%), and, in terms of both the evaluated sowing times and cultivars, the highest oil production rates were found in the Balci cultivar (32.20% and 31.78%) for both sowing times. It was determined that there is a positive and significant (r=0.476⁎⁎) relationship between oil with protein production rates but a negative and significant relationship between oil and linolenic acid production rates (r=-0.728⁎⁎). The oleic acid production rate was strongly negatively and significantly correlated with the linoleic acid production rate (r=-0.997⁎⁎).

再生可能エネルギーの貯蔵に向けた CO<sub>2</sub> 電気化学還元によるギ酸製造

For the storage of the renewable energy using formic aid, the combination of the direct formic acid fuel cell which can directly produce the electric power using formic acid and the CO2 electrochemical reduction (ERC) which can produce the formic acid using the electric power derived from the renewable energy and CO2 emitted from direct formic acid fuel cell has been proposed. In order to achieve this process, improvement of the formic acid production rate is required. It has been known that formic acid could be obtained at high yield Sn catalyst at ERC, however, production rate was still low due to the high overpotential. In this study, the supported Sn catalyst has been produced for the enhancement of the production rate of the formic acid by ERC. It was found that supported Sn catalyst showed higher CO2 reduction current comparing to that obtained by conventional Sn nano particles.

Production of orotic acid by a Klura3Δ mutant of Kluyveromyces lactis

We demonstrated that a Klura3Δ, mutant of the yeast Kluyveromyces lactis is able to produce and secrete into the growth medium considerable amounts of orotic acid. Using yeast extract-peptone-glucose (YPD) based media we optimized production conditions in flask and bioreactor cultures. With cells grown in YPD 5% glucose medium, the best production in flask was obtained with a 1:12.5 ratio for flask: culture volume, 180rpm, 28°C and 200mM MOPS for pH stabilization at neutral values (initial culture pH at 8.0). The best production in a 2L bioreactor was achieved at 500rpm with 1vvm aeration, 28°C and pH 7.0. Under these optimum conditions, similar rates of orotic acid production were obtained and maximum concentration achieved after 96h was 6.7g/L in flask and bioreactor cultures. These results revealed an excellent reproducibility between both systems and provided evidence for the biotechnological potential of Klura3Δ strain to produce orotic acid since the amounts obtained are comparable to the production in flask using a similar mutant of the industrially valuable Corynebacterium glutamicum.

EFFECT OF SOYA AND WHEY PROTEINS ON THE SENSORY AND PHYSICOCHEMICAL PROPERTIES OF SET YOGHURT

Recently, a focus on the utilization of whey and soya proteins has been receiving significant attention due to their nutritional value and their potential to enhance the functional characteristics of the dairy products. Set yoghurt was manufactured from standardized (4% fat) buffalo milk alone (control), or fortified with whey protein concentrate (WPC), soya protein concentrate (SPC) or their combination (MIX) and stored at 5±2 °C for 10 days. Sensory properties of the resultant yoghurt were evaluated one day after manufacturing. All treatments were analyzed when fresh and during storage period for pH-value, titratable acidity(TA) and syneresis. The pH-values and titratable acidity(TA) of yoghurt samples showed that both soya and whey proteins did not alter the rate of acid production in yoghurt. Acidity of samples treated with WPC during storage was significantly (P<0.05) higher, compared to control. Also, the addition of whey proteins and soya proteins or their combination resulted in reduction in the syneresis of yoghurt samples by about 17-25%, when compared with control at zero time. Fortification with soya proteins lowered appearance, taste and odor scores by 25, 37 and 35%, respectively, compared with the control. This negative effect of soya proteins on the sensory properties of yoghurt (SPC treatment) was improved when combined with whey protein in the MIX treatment. Therefore, it is recommended to add whey proteins to improve sensory and syneresis properties of soya yoghurt.

Bioaugmentation of Lactobacillus delbrueckii ssp. bulgaricus TISTR 895 to enhance bio-hydrogen production of Rhodobacter sphaeroides KKU-PS5.

BackgroundBioaugmentation or an addition of the desired microorganisms or specialized microbial strains into the anaerobic digesters can enhance the performance of microbial community in the hydrogen production process. Most of the studies focused on a bioaugmentation of native microorganisms capable of producing hydrogen with the dark-fermentative hydrogen producers while information on bioaugmentation of purple non-sulfur photosynthetic bacteria (PNSB) with lactic acid-producing bacteria (LAB) is still limited. In our study, bioaugmentation of Rhodobacter sphaeroides KKU-PS5 with Lactobacillus delbrueckii ssp. bulgaricus TISTR 895 was conducted as a method to produce hydrogen. Unfortunately, even though well-characterized microorganisms were used in the fermentation system, a cultivation of two different organisms in the same bioreactor was still difficult because of the differences in their metabolic types, optimal conditions, and nutritional requirements. Therefore, evaluation of the physical and chemical factors affecting hydrogen production of PNSB augmented with LAB was conducted using a full factorial design followed by response surface methodology (RSM) with central composite design (CCD).ResultsA suitable LAB/PNSB ratio and initial cell concentration were found to be 1/12 (w/w) and 0.15 g/L, respectively. The optimal initial pH, light intensity, and Mo concentration obtained from RSM with CCD were 7.92, 8.37 klux and 0.44 mg/L, respectively. Under these optimal conditions, a cumulative hydrogen production of 3396 ± 66 mL H2/L, a hydrogen production rate (HPR) of 9.1 ± 0.2 mL H2/L h, and a hydrogen yield (HY) of 9.65 ± 0.23 mol H2/mol glucose were obtained. KKU-PS5 augmented with TISTR 895 produced hydrogen from glucose at a relatively high HY, 9.65 ± 0.23 mol H2/mol glucose, i.e., 80 % of the theoretical yield.ConclusionsThe ratio of the strains TISTR 895/KKU-PS5 and their initial cell concentrations affected the rate of lactic acid production and its consumption. A suitable LAB/PNSB ratio and initial cell concentration could balance the lactic acid production rate and its consumption in order to avoid lactic acid accumulation in the fermentation system. Through use of appropriate environmental conditions for bioaugmentation of PNSB with LAB, a hydrogen production could be enhanced.Electronic supplementary materialThe online version of this article (doi:10.1186/s13068-015-0375-z) contains supplementary material, which is available to authorized users.

Seasonal Changes in Mycosporine-Like Amino Acid Production Rate with Respect to Natural Phytoplankton Species Composition.

After in situ incubation at the site for a year, phytoplanktons in surface water were exposed to natural light in temperate lakes (every month); thereafter, the net production rate of photoprotective compounds (mycosporine-like amino acids, MAAs) was calculated using 13C labeled tracer. This is the first report describing seasonal variation in the net production rate of individual MAAs in temperate lakes using a compound-specific stable isotope method. In the mid-latitude region of the Korean Peninsula, UV radiation (UVR) usually peaks from July to August. In Lake Paldang and Lake Cheongpyeong, diatoms dominated among the phytoplankton throughout the year. The relative abundance of Cyanophyceae (Anabaena spiroides) reached over 80% during July in Lake Cheongpyeong. Changes in phytoplankton abundance indicate that the phytoplankton community structure is influenced by seasonal changes in the net production rate and concentration of MAAs. Notably, particulate organic matter (POM) showed a remarkable change based on the UV intensity occurring during that period; this was because of the fact that cyanobacteria that are highly sensitive to UV irradiance dominated the community. POM cultured in Lake Paldang had the greatest shinorine (SH) production rate during October, i.e., 83.83 ± 10.47 fgC·L−1·h−1. The dominance of diatoms indicated that they had a long-term response to UVR. Evaluation of POM cultured in Lake Cheongpyeong revealed that there was an increase in the net MAA production in July (when UVR reached the maximum); a substantial amount of SH, i.e., 17.62 ± 18.34 fgC·L−1·h−1, was recorded during this period. Our results demonstrate that both the net production rate as well as the concentration of MAAs related to photoinduction depended on the phytoplankton community structure. In addition, seasonal changes in UVR also influenced the quantity and production of MAAs in phytoplanktons (especially Cyanophyceae).

High Acetic Acid Production Rate Obtained by Microbial Electrosynthesis from Carbon Dioxide.

High product specificity and production rate are regarded as key success parameters for large-scale applicability of a (bio)chemical reaction technology. Here, we report a significant performance enhancement in acetate formation from CO2, reaching comparable productivity levels as in industrial fermentation processes (volumetric production rate and product yield). A biocathode current density of -102 ± 1 A m(-2) and an acetic acid production rate of 685 ± 30 (g m(-2) day(-1)) have been achieved in this study. High recoveries of 94 ± 2% of the CO2 supplied as the sole carbon source and 100 ± 4% of electrons into the final product (acetic acid) were achieved after development of a mature biofilm, reaching an elevated product titer of up to 11 g L(-1). This high product specificity is remarkable for mixed microbial cultures, which would make the product downstream processing easier and the technology more attractive. This performance enhancement was enabled through the combination of a well-acclimatized and enriched microbial culture (very fast start-up after culture transfer), coupled with the use of a newly synthesized electrode material, EPD-3D. The throwing power of the electrophoretic deposition technique, a method suitable for large-scale production, was harnessed to form multiwalled carbon nanotube coatings onto reticulated vitreous carbon to generate a hierarchical porous structure.

A comparative evaluation of different types of microbial electrolysis desalination cells for malic acid production

The aim of this study was to investigate different microbial electrolysis desalination cells for malic acid production. The systems included microbial electrolysis desalination and chemical-production cell (MEDCC), microbial electrolysis desalination cell (MEDC) with bipolar membrane and anion exchange membrane (BP-A MEDC), MEDC with bipolar membrane and cation exchange membrane (BP-C MEDC), and modified microbial desalination cell (M-MDC). The microbial electrolysis desalination cells performed differently in terms of malic acid production and energy consumption. The MEDCC performed best with the highest malic acid production rate (18.4±0.6mmol/Lh) and the lowest energy consumption (0.35±0.14kWh/kg). The best performance of MEDCC was attributable to the neutral pH condition in the anode chamber, the lowest internal resistance, and the highest Geobacter percentage of the anode biofilm population among all the reactors.

Advanced green biorefining: effects of ensiling treatments on lactic acid production, microbial activity and supplementary methane formation of grass and rye

For a more eco-friendly production of energy and chemicals (e.g. lactic acid), green biorefineries are implementing an environmentally conscious technique of using green biomass. To increase the amount of lactic acid in grass and rye silage, different ensiling treatments were conducted. Additionally, after separating the organic juice, the specific methane yield of the remaining solid residue of the ensiled material was determined. The amount of lactic acid was increased by 168.8 % (149.7 ± 20.9 g kg−1 dry matter (DM)) through applying homofermentative lactic acid bacteria together with carbonated lime to the raw material grass. For rye, while having a stable silage, the highest increase in lactic acid was achieved by chopping the raw material to a theoretical length of cut of 1 mm. As a result, an increase of 46.3 % (57.5 ± 0.6 g kg−1 DM) was attained. Taxonomic profiling by 16S amplicon sequencing revealed that the homofermentative species Lactobacillus plantarum was the most dominant species on both substrates with highest lactic acid production rate, though its growth on rye led to unstable silage conditions with butyric acid producing Clostridia. The specific methane yields of the corresponding solid residues were determined to be 335.7 ± 7.2 lN kg−1 organic dry matter (ODM) for grass and at 235.0 ± 2.6 lN kg−1 ODM for rye.

Regulating the production of (R)-3-hydroxybutyrate in Escherichia coli by N or P limitation.

The chiral compound (R)-3-hydroxybutyrate (3HB) is naturally produced by many wild type organisms as the monomer for polyhydroxybutyrate (PHB). Both compounds are commercially valuable and co-polymeric polyhydroxyalkanoates have been used e.g., in medical applications for skin grafting and as components in pharmaceuticals. In this paper we investigate cultivation strategies for production of 3HB in the previously described E. coli strain AF1000 pJBGT3RX. This strain produces extracellular 3HB by expression of two genes from the PHB pathway of Halomonas boliviensis. H. boliviensis is a newly isolated halophile that forms PHB as a storage compound during carbon excess and simultaneous limitation of another nutrient like nitrogen and phosphorous. We hypothesize that a similar approach can be used to control the flux from acetyl-CoA to 3HB also in E. coli; decreasing the flux to biomass and favoring the pathway to the product. We employed ammonium- or phosphate-limited fed-batch processes for comparison of the productivity at different nutrient limitation or starvation conditions. The feed rate was shown to affect the rate of glucose consumption, respiration, 3HB, and acetic acid production, although the proportions between them were more difficult to affect. The highest 3HB volumetric productivity, 1.5 g L−1 h−1, was seen for phosphate-limitation.

Glucose Addiction in Cancer Therapy: Advances and Drawbacks.

While normal differentiated cells primarily use mitochondrial respiration to generate the required energy for cellular processes, most cancer cells rely on glycolysis, even in sufficient oxygen conditions. This phenomenon is known as the "Warburg effect" or aerobic glycolysis and the metabolic reprogramming of cancer cells towards this altered energy metabolism is currently recognized as one of the "hallmarks of cancer". Aerobic glycolysis underlies the rapid growth of tumor cells, with high rates of glucose consumption and lactic acid production, leading to cellular acidosis. Metabolic reprogramming renders cancer cells dependent on specific metabolic enzymes or pathways that could be exploited in cancer therapy. The development of treatments that target tumor glucose metabolism is receiving renewed attention, with several drugs targeting metabolic pathways currently in clinical trials. The search for suitable targets, however, is limited by the high plasticity of the metabolic network that can induce compensatory routes. Deregulated glucose metabolism is a prominent feature associated with resistance to classical chemotherapy or oncogene-targeted therapies, strengthening the clinical potential of combining these therapies with glycolysis inhibitors. The aim of this review is to compare the advances of different therapeutic strategies targeting the glucose "addiction" of tumor cells, highlighting their potential as effective weapons against cancer. We further discuss recent evidence for the involvement of glucose metabolism as a compensatory response to the use of drugs that target different signaling pathways, where the combination with glycolysis inhibitors could prove extraordinarily useful.

Flux balance analysis in the production of clavulanic acid byStreptomyces clavuligerus

In this work, in silico flux balance analysis is used for predicting the metabolic behavior of Streptomyces clavuligerus during clavulanic acid production. To choose the best objective function for use in the analysis, three different optimization problems are evaluated inside the flux balance analysis formulation: (i) maximization of the specific growth rate, (ii) maximization of the ATP yield, and (iii) maximization of clavulanic acid production. Maximization of ATP yield showed the best predictions for the cellular behavior. Therefore, flux balance analysis using ATP as objective function was used for analyzing different scenarios of nutrient limitations toward establishing the effect of limiting the carbon, nitrogen, phosphorous, and oxygen sources on the growth and clavulanic acid production rates. Obtained results showed that ammonia and phosphate limitations are the ones most strongly affecting clavulanic acid biosynthesis. Furthermore, it was possible to identify the ornithine flux from the urea cycle and the α-ketoglutarate flux from the TCA cycle as the most determinant internal fluxes for promoting clavulanic acid production.

Identification of anti-biofilm components in Withania somnifera and their effect on virulence of Streptococcus mutans biofilms.

The aim of this study was to identify components of the Withania somnifera that could show anti-virulence activity against Streptococcus mutans biofilms. The anti-acidogenic activity of fractions separated from W. somnifera was compared, and then the most active anti-acidogenic fraction was chemically characterized using gas chromatography-mass spectroscopy. The effect of the identified components on the acidogenicity, aciduricity and extracellular polymeric substances (EPS) formation of S. mutans UA159 biofilms was evaluated. The change in accumulation and acidogenicity of S. mutans UA159 biofilms by periodic treatments (10 min per treatment) with the identified components was also investigated. Of the fractions, n-hexane fraction showed the strongest anti-acidogenic activity and was mainly composed of palmitic, linoleic and oleic acids. Of the identified components, linoleic and oleic acids strongly affected the acid production rate, F-ATPase activity and EPS formation of the biofilms. Periodic treatment with linoleic and oleic acids during biofilm formation also inhibited the biofilm accumulation and acid production rate of the biofilms without killing the biofilm bacteria. These results suggest that linoleic and oleic acids may be effective agents for restraining virulence of S. mutans biofilms. Linoleic and oleic acids may be promising agents for controlling virulence of cariogenic biofilms and subsequent dental caries formation.

Metabolic profiling of hematopoietic stem and progenitor cells during proliferation and differentiation into red blood cells

An understanding of the metabolic profile of cell proliferation and differentiation should support the optimization of culture conditions for hematopoietic stem and progenitor cell (HSPC) proliferation, differentiation, and maturation into red blood cells. We have evaluated the key metabolic parameters during each phase of HSPC culture for red blood cell production in serum-supplemented (SS) and serum-free (SF) conditions. A simultaneous decrease in growth rate, total protein content, cell size, and the percentage of cells in the S/G2 phase of cell cycle, as well as an increase in the percentage of cells with a CD71(-)/GpA(+) surface marker profile, indicates HSPC differentiation into red blood cells. Compared with proliferating HSPCs, differentiating HSPCs showed significantly lower glucose and glutamine consumption rates, lactate and ammonia production rates, and amino acid consumption and production rates in both SS and SF conditions. Furthermore, extracellular acidification was associated with late proliferation phase, suggesting a reduced cellular metabolic rate during the transition from proliferation to differentiation. Under both SS and SF conditions, cells demonstrated a high metabolic rate with a mixed metabolism of both glycolysis and oxidative phosphorylation (OXPHOS) in early and late proliferation, an increased dependence on OXPHOS activity during differentiation, and a shift to glycolytic metabolism only during maturation phase. These changes indicate that cell metabolism may have an important impact on the ability of HSPCs to proliferate and differentiate into red blood cells.

Ultraviolet C light pathogen inactivation treatment of platelet concentrates preserves integrin activation but affects thrombus formation kinetics on collagen in vitro.

Ultraviolet (UV) light illumination in the presence of exogenously added photosensitizers has been used to inactivate pathogens in platelet (PLT) concentrates for some time. The THERAFLEX UV-C system, however, illuminates PLT concentrates with UV-C light without additional photoactive compounds. In this study residual PLT function is measured in a comprehensive paired analysis of UV-C-treated, gamma-irradiated, and untreated control PLT concentrates. A pool-and-split design was used with buffy coat-derived PLT concentrates in 65% SSP+ additive solution. Thrombus formation kinetics in microfluidic flow chambers onto immobilized collagen was investigated with real-time video microscopy. PLT aggregation, membrane markers, and cellular metabolism were determined concurrently. Compared to gamma-treated and untreated controls, UV-C treatment significantly affected thrombus formation rates on Days5 and 7, not Day2. PLT degranulation (P-selectin) and PLT apoptosis (annexinV binding) was slightly but significantly increased from Day2 on. UV-C treatment moreover induced integrin αIIb β3 conformational changes reminiscent of activation. However, subsequent integrin activation by either PAR1-activating hexapeptide (PAR1AP) or convulxin was unaffected. This was confirmed by PLT aggregation studies induced with collagen, PAR1AP, and ristocetin at two different agonist concentrations. Finally, UV-C slightly increased lactic acid production rates, resulting in significantly decreased pH on Days5 and 7, but never dropped below 7.2. UV-C pathogen inactivation treatment slightly but significantly increases PLT activation markers but does not profoundly influence activatability nor aggregation. The treatment does, however, attenuate thrombus formation kinetics in vitro in microfluidic flow chambers, especially after storage.

Overexpression of Small Heat Shock Protein Enhances Heat- and Salt-Stress Tolerance of Bifidobacterium longum NCC2705.

Bifidobacteria are probiotics that are incorporated live into various dairy products. They confer health-promotive effects via gastrointestinal tract colonization. However, to provide their health-beneficial properties, they must battle the various abiotic stresses in that environment, such as bile salts, acids, oxygen, and heat. In this study, Bifidobacterium longum salt- and heat-stress tolerance was enhanced by homologous overexpression of a small heat shock protein (sHsp). A positive contribution of overproduced sHsp to abiotic stress tolerance was observed when the bacterium was exposed to heat and salt stresses. Significantly higher survival of B. l ongum NCC2705 overexpressing sHsp was observed at 30 and 60min into heat (55 °C) and salt (5M NaCl) treatment, respectively. Thermotolerance analysis at 47°C with sampling every 2h also revealed the great potential tolerance of the engineered strain. Cell density and acid production rate increased for the sHsp-overexpressing strain after 8 and 10h of both heat and salt stresses. In addition, tolerance to bile salts, low pH (3.5) and low temperature (4°C) was also increased by homologous overexpression of the sHsp hsp20 in B. l ongum. Results revealed that hsp20 overexpression in B longum NCC2705 plays a positive cross-protective role in upregulating abiotic responses, ensuring the organism's tolerance to various stress conditions; therefore, sHsp-overexpressing B. l ongum is advised for fermented dairy foods and other probiotic product applications.

Effect of carbonic anhydrase on enzymatic conversion of CO2 to formic acid and optimization of reaction conditions

Enzymatic reduction of CO2 to formic acid promises the production of high-value chemicals from greenhouse gases in the way of high selectivity and low energy consumption. However, slow hydration process of CO2 in reaction solution leads to low production rate of formic acid. Carbonic anhydrase (CA), a vigorous biocatalyst for CO2 hydration, has attracted much attention for its potential applications in CO2 capture and sequestration in recent years, while its use in biosynthesis of chemicals and fuels based on CO2 has hardly been reported. Herein we report the feasibility of CA in facilitating biosynthesis of formic acid from CO2 with the catalysis of formate dehydrogenase (FDH), and various reaction conditions were optimized for the first time. With the addition of CA, the substrate of FDH might transform from CO2 to more soluble HCO3−, together with the increase in the hydration rate of CO2, resulting in that the production rate of formic acid was increased by a factor of 4.2-fold. Due to the decrease in pH value induced by CA with the reaction proceeded, the ratio of two enzymes was important to coordinate the reaction rate and avoid the accumulation of hydrogen ions, at the same time, buffer system was critical to ensure the synergize effect of CA. It appeared to us that the introduction of CA represents a new bioprocessing strategy for efficient biotansformation of CO2 to formic acid and its further products.