pH Unit Difference Research Articles

Effect of abattoir, livestock species and storage temperature on bacterial community dynamics and sensory properties of vacuum packaged red meat

Shelf life of red meat is influenced by a number of intrinsic and extrinsic factors making its prediction challenging. Here we investigated the influence of geographically distant abattoir facilities and storage temperature relevant to commercial supply chain on the shelf lives of vacuum packaged (VP) beef and lamb meat. Samples of VP beef and lamb were analysed for surface pH, total viable counts, lactic acid bacterial counts, sensory properties, and associated bacterial community using Illumina MiSeq based 16S rRNA gene amplicon sequencing over a period of >200 days. The consistent 0.41 pH unit difference between beef and lamb was found to have a profound effect on bacterial community diversity and composition, bacterial growth rates and the rate of loss of sensory quality. Though different community structures were derived from different abattoir source, bacterial growth rate and rate of sensory quality deterioration were found to be comparable for individual meat type. The greatest variation in rates was found resulting from storage temperature and livestock species themselves. Our findings indicate that bacterial growth and sensory quality loss are essentially predictable when considering their temperature dependency, however for successful meat export validation of shelf life predictive models is required due to stochastic variation in abattoir seeded bacterial populations.

Constructing artificial respiratory chain in polymer compartments: Insights into the interplay between bo3 oxidase and the membrane.

Cytochrome bo3 ubiquinol oxidase is a transmembrane protein, which oxidizes ubiquinone and reduces oxygen, while pumping protons. Apart from its combination with F1Fo-ATPase to assemble a minimal ATP regeneration module, the utility of the proton pump can be extended to other applications in the context of synthetic cells such as transport, signaling, and control of enzymatic reactions. In parallel, polymers have been speculated to be phospholipid mimics with respect to their ability to self-assemble in compartments with increased stability. However, their usability as interfaces for complex membrane proteins has remained questionable. In the present work, we optimized a fusion/electroformation approach to reconstitute bo3 oxidase in giant unilamellar vesicles made of PDMS-g-PEO and/or phosphatidylcholine (PC). This enabled optical access, while microfluidic trapping allowed for online analysis of individual vesicles. The tight polymer membranes and the inward oriented enzyme caused 1 pH unit difference in 30 min, with an initial rate of 0.35 pH·min-1 To understand the interplay in these composite systems, we studied the relevant mechanical and rheological membrane properties. Remarkably, the proton permeability of polymer/lipid hybrids decreased after protein insertion, while the latter also led to a 20% increase of the polymer diffusion coefficient in polymersomes. In addition, PDMS-g-PEO increased the activity lifetime and the resistance to free radicals. These advantageous properties may open diverse applications, ranging from cell-free biotechnology to biomedicine. Furthermore, the presented study serves as a comprehensive road map for studying the interactions between membrane proteins and synthetic membranes, which will be fundamental for the successful engineering of such hybrid systems.

Interactions of organic acids with vancomycin-resistant Enterococcus faecium isolated from community wastewater in Texas.

Investigate the interactions of organic acids (OAs), acetic, butyric, citric, formic, lactic and propionic acid against 50 Gram-positive vancomycin-resistant Enterococcus faecium (VRE) strains to determine whether pH, undissociated or dissociated acid forms correlate with bacterial inhibition. Concentrations of undissociated and dissociated OAs at the molar minimum inhibitory concentrations (MICM s) of the VRE were calculated using the Henderson-Hasselbalch equation. The pH at the MICM s of all VRE strains against acetic, butyric, formic and propionic acids was similar, 4·66±0·07, but there was a 1·1 pH unit difference for all six OAs. Inhibition of VRE by all six OAs did not appear to be solely dependent on pH or on the undissociated OA species. The inhibition of VRE by all six dissociated acids was within Δ=3·1mmoll-1 . Vancomycin-resistant Enterococcus faecium inhibition correlated with the dissociated OA species. A small decrease in the concentration of the dissociated OAs from optimum may result in allowing VRE strains to escape disinfection. When an OA is used to disinfect VRE strains, the concentration of the dissociated OA should be carefully controlled. A concentration of at least 20mmoll-1 dissociated OA should be maintained when disinfecting VRE.

Tailoring Microbial Electrochemical Cells for Production of Hydrogen Peroxide at High Concentrations and Efficiencies.

A microbial peroxide producing cell (MPPC) for H2 O2 production at the cathode was systematically optimized with minimal energy input. First, the stability of H2 O2 was evaluated using different catholytes, membranes, and catalyst materials. On the basis of these results, a flat-plate MPPC fed continuously using 200 mm NaCl catholyte at a 4 h hydraulic retention time was designed and operated, producing H2 O2 for 18 days. H2 O2 concentration of 3.1 g L-1 H2 O2 with 1.1 Wh g-1 H2 O2 power input was achieved in the MPPC. The high H2 O2 concentration was a result of the optimum materials selected. The small energy input was largely the result of the 0.5 cm distance between the anode and cathode, which reduced ionic transport losses. However, >50 % of operational overpotentials were due to the 4.5-5 pH unit difference between the anode and cathode chambers. The results demonstrate that a MPPC can continuously produce H2 O2 at high concentration by selecting compatible materials and appropriate operating conditions.

Catalytic Capacity of Diaza-Crown Ether Lanthanum Complexes with Varied Ligands for Phosphate Ester Hydrolysis in Different Media

Two diaza-crown ether compounds, 1,4,10,13-tetraoxa-7,16-diazacyclooctadecane (L0) and its derivative with double acetamide side arms 2,2'-(1,4,10,13-teteaoxa-7,16-diazacyclooctadecane-7,16-diyl)diacetamide (L), and the corresponding two lanthanum complexes were synthesised and characterised. The catalytic capacity of the lanthanum complexes was investigated for the hydrolysis of bis(4-nitrophenyl) phosphate ester (BNPP) in aqueous solution and in CTAB micelles. Kinetic studies show that the catalytic efficiency of complex LaL is obviously higher than that of complex LaL0, and introducing acetamide into the ring of the diaza-crown ether can improve the catalytic ability of the complexes for BNPP hydrolysis. A rate enhancement of about two times was observed for the complex–micelle in contrast with the complex–water system for BNPP catalytic hydrolysis. The optimal pH for the catalytic reaction in the two kinds of media systems show an approximately 0.4 pH unit difference. The two complexes possess higher thermostability, and are more stable in the micelle than in aqueous solution. Based on the results and their analysis, a catalytic mechanism with cooperation of acetamide is proposed.

Integration of a Droplet-Based Microfluidic System and Silicon Nanoribbon FET Sensor.

We present a novel microfluidic system that integrates droplet microfluidics with a silicon nanoribbon field-effect transistor (SiNR FET), and utilize this integrated system to sense differences in pH. The device allows for selective droplet transfer to a continuous water phase, actuated by dielectrophoresis, and subsequent detection of the pH level in the retrieved droplets by SiNR FETs on an electrical sensor chip. The integrated microfluidic system demonstrates a label-free detection method for droplet microfluidics, presenting an alternative to optical fluorescence detection. In this work, we were able to differentiate between droplet trains of one pH-unit difference. The pH-based detection method in our integrated system has the potential to be utilized in the detection of biochemical reactions that induce a pH-shift in the droplets.

Strong dependence between phytoplankton and water chemistry in a large temperate lake: spatial and temporal perspective

In lakes, spatial and temporal variability of water chemistry and phytoplankton are characteristic phenomena although often difficult to link together. This motivated us to study their interplay in Lake Vanajanselka, a eutrophic lake in Finland. We hypothesized that in summer spatial and temporal differences in phytoplankton and water chemistry can be extended in comparison to spring and autumn. Therefore, chlorophyll a and water chemistry was examined by six sampling campaigns with 15 sampling sites over the lake in May–October 2009–2010. In summer, chlorophyll, pH, and oxygen were horizontally and vertically unevenly distributed in the lake, and in the epilimnion pH and oxygen showed a distinct diurnal variability suggesting high photosynthesis during the day. Daily >1 pH unit difference between the sites and 2.5 pH unit difference between the epi- and hypolimnion were found. In agreement with pH and oxygen, NO3-N and NH4-N could be unevenly distributed in the epilimnion. In autumn no spatial differences were found, however. The results emphasized that algae and cyanobacteria were responsible, at least partly, for the variability in water chemistry in the surface layer, and short- and long-term gradients in space and time need to be considered when productive lakes are studied.

Anthrax Toxin Receptor 2 Determinants that Dictate the pH Threshold of Toxin Pore Formation

The anthrax toxin receptors, ANTXR1 and ANTXR2, act as molecular clamps to prevent the protective antigen (PA) toxin subunit from forming pores until exposure to low pH. PA forms pores at pH ∼6.0 or below when it is bound to ANTXR1, but only at pH ∼5.0 or below when it is bound to ANTXR2. Here, structure-based mutagenesis was used to identify non-conserved ANTXR2 residues responsible for this striking 1.0 pH unit difference in pH threshold. Residues conserved between ANTXR2 and ANTXR1 that influence the ANTXR2-associated pH threshold of pore formation were also identified. All of these residues contact either PA domain 2 or the neighboring edge of PA domain 4. These results provide genetic evidence for receptor release of these regions of PA as being necessary for the protein rearrangements that accompany anthrax toxin pore formation.

Extracellular and intracellular acid-base effects of submergence anoxia and nitrogen breathing in turtles

We compared extracellular and intracellular acid-base state in turtles ( Chrysemys picta bellii) subjected to anoxic submergence to turtles made anoxic by N 2-breathing. Measurements made on control animals and on animals after 1,2,4, or 6 h of anoxia included blood pH, P O 2 , P CO 2 , and lactate as well as liver, heart, skeletal muscle, and brain pH i (using DMO equilibration), lactate, and glycogen concentrations. We hypothesized that the anaerobic metabolic rate of submerged turtles would be depressed by the more severe extra- and intracellular acidosis, and that this would be indicated by reduced lactate accumulation and glycogen depletion. Submerged turtles became extremely acidemic due to a combined metabolic and respiratory acidosis and had significantly lower arterial pH than N 2-breathing animals (6.98 and 7.34, respectively, after 6 h). In spite of this disparity in pH a, 6 h pH i values for liver, heart, and brain were similar. Likewise, our data on glycogen depletion and lactate accumulation at h 6 in these tissues suggest no dramatic differences in anaerobic metabolic rate. While skeletal muscle pH i was somewhat lower at h 6 in the submerged group (6.73 vs 6.91 for N 2-breathers), we observed no differences in either glycogen depletion or lactate accumulation in this tissue between our two treatments. Thus, at h 6, in spite of a 0.37 pH unit difference in pH a and a nearly 70 mm Hg difference in arterial and presumably cytosolic P CO 2 , pH i and tissue lactate and glycogen concentrations were similar. These results can be explained if the in vivo intracellular buffer values (β) of turtle tissues are very high. We conclude that extracellular acid-base state is not necessarily reflected intracellularly in vivo in turtles and care must be taken in extrapolating from one compartment to another when attempting to make inferences about metabolic depression or acid-base regulation in this species.