Rate Of pH Change Research Articles

Natural variability and anthropogenic change in equatorial Pacific surface ocean pCO2 and pH

AbstractThe equatorial Pacific is a dynamic region that plays an important role in the global carbon cycle. This region is the largest oceanic source of carbon dioxide (CO2) to the atmosphere, which varies interannually dependent on the El Niño‐Southern Oscillation (ENSO) and other climatic and oceanic drivers. We present high‐resolution observations of surface ocean CO2 partial pressure (pCO2) at four fixed locations in the Niño 3.4 area with data sets encompassing 10 ENSO warm and cold events from 1997 to 2011. The mooring observations confirm that ENSO controls much of the interannual variability in surface seawater pCO2 with values ranging from 315 to 578 µatm. The mooring time series also capture the temporal variability necessary to make the first estimates of long‐term pH trends in the equatorial Pacific, which suggests that the combination of ocean acidification and decadal variability creates conditions for high rates of pH change since the beginning of the mooring record. Anthropogenic CO2 increases play a dominant role in significant observed seawater pCO2 trends of +2.3 to +3.3 µatm yr−1 and pH trends of −0.0018 to −0.0026 yr−1 across the full time series in this region. However, increased upwelling driven by increased trade winds, a shallower thermocline, and increased frequency of La Niña events also contribute an average of 40% of the observed trends since 1998. These trends are higher than previous estimates based on underway observations and suggest that the equatorial Pacific is contributing a greater amount of CO2 to the atmospheric CO2 inventory over the last decade.

Coralline algal structure is more sensitive to rate, rather than the magnitude, of ocean acidification

Marine pCO2 enrichment via ocean acidification (OA), upwelling and release from carbon capture and storage (CCS) facilities is projected to have devastating impacts on marine biomineralisers and the services they provide. However, empirical studies using stable endpoint pCO2 concentrations find species exhibit variable biological and geochemical responses rather than the expected negative patterns. In addition, the carbonate chemistry of many marine systems is now being observed to be more variable than previously thought. To underpin more robust projections of future OA impacts on marine biomineralisers and their role in ecosystem service provision, we investigate coralline algal responses to realistically variable scenarios of marine pCO2 enrichment. Coralline algae are important in ecosystem function; providing habitats and nursery areas, hosting high biodiversity, stabilizing reef structures and contributing to the carbon cycle. Red coralline marine algae were exposed for 80 days to one of three pH treatments: (i) current pH (control); (ii) low pH (7.7) representing OA change; and (iii) an abrupt drop to low pH (7.7) representing the higher rates of pH change observed at natural vent systems, in areas of upwelling and during CCS releases. We demonstrate that red coralline algae respond differently to the rate and the magnitude of pH change induced by pCO2 enrichment. At low pH, coralline algae survived by increasing their calcification rates. However, when the change to low pH occurred at a fast rate we detected, using Raman spectroscopy, weaknesses in the calcite skeleton, with evidence of dissolution and molecular positional disorder. This suggests that, while coralline algae will continue to calcify, they may be structurally weakened, putting at risk the ecosystem services they provide. Notwithstanding evolutionary adaptation, the ability of coralline algae to cope with OA may thus be determined primarily by the rate, rather than magnitude, at which pCO2 enrichment occurs.

Effect of pH Change on the Shell Thickness of Calcium Carbonate Hollow Particles by CO2 Gas Bubbling Method

Effect of pH change on the shell thickness of calcium carbonate hollow particles was investigated. Calcium carbonate hollow particles were synthesized at different pH change rates by Carbon dioxide bubbling into a solution. And influence of pH change rate on the shell thickness was estimated by observing SEM images of cross section of hollow particles. pH change curve could be divided into two stages, before and after the point where pH changes rapidly, and could express each stage with the approximated curve. Rate parameters of pH change rate were determined from these approximated curves, and the relation with shell thickness was investigated. As a result, it has become clear that thickness of hollow particles is expressible by the rate parameter of approximation curve corresponding to the first stage which is characterized as the process from start of bubbling to the point where shell is formed.

Different Natriuretic Responses in Obese and Lean Rats in Response to Nitric Oxide Reduction

Nitric oxide (NO) is an important regulator of renal sodium transport and participates in the control of natriuresis and diuresis. In obesity, the nitric oxide bioavailability was reportedly reduced, which may contribute to the maintenance of hypertension. The aim of this study was to determine the effect of NO depletion on renal sodium handling in a model of diet-induced obesity hypertension. Obese hypertensive (obesity-prone (OP)) and lean normotensive (obesity-resistant (OR)) Sprague-Dawley rats were treated with 1.2 mg/kg/day N(G)-nitro-L-arginine-methyl ester (L-NAME) for 4 weeks to inhibit NO synthesis. Acute pressure natriuresis and diuresis were measured in response to an increase in perfusion pressure. NHE3 and Na(+), K(+)-ATPase protein expression were measured by Western blot and NHE3 activity was determined as the rate of pH change in brush border membrane vesicles. NHE3 membrane localization was determined by confocal microscopy. L-NAME did not significantly attenuate the natriuretic and diuretic responses to increases in renal perfusion pressure (RPP) in OP rats while inducing a significant reduction in OR rats. Following chronic NO inhibition, NHE3 protein expression and activity and Na(+), K(+)-ATPase protein expression were significantly increased in the OR but not in the OP group. Immunofluorescence studies indicated that the increase in NHE3 activity could be, at least in part, due to NHE3 membrane trafficking. Obese hypertensive rats have a weaker natriuretic response in response to NO inhibition compared to lean rats and the mechanism involves different regulation of the apical sodium exchanger NHE3 expression, activity, and trafficking.

Cytosolic H+ microdomain developed around AE1 during AE1‐mediated Cl−/HCO3− exchange

Microdomains, regions of discontinuous cytosolic solute concentration enhanced by rapid solute transport and slow diffusion rates, have many cellular roles. pH-regulatory membrane transporters, like the Cl−/HCO3− exchanger AE1, could develop H+ microdomains since AE1 has a rapid transport rate and cytosolic H+ diffusion is slow. We examined whether the pH environment surrounding AE1 differs from other cellular locations. As AE1 drives Cl−/HCO3− exchange, differences in pH, near and remote from AE1, were monitored by confocal microscopy using two pH-sensitive fluorescent proteins: deGFP4 (GFP) and mNectarine (mNect). Plasma membrane (PM) pH (defined as ∼1 μm region around the cell periphery) was monitored by GFP fused to AE1 (GFP.AE1), and mNect fused to an inactive mutant of the Na+-coupled nucleoside co-transporter, hCNT3 (mNect.hCNT3). GFP.AE1 to mNect.hCNT3 distance was varied by co-expression of different amounts of the two proteins in HEK293 cells. As the GFP.AE1–mNect.hCNT3 distance increased, mNect.hCNT3 detected the Cl−/HCO3− exchange-associated cytosolic pH change with a time delay and reduced rate of pH change compared to GFP.AE1. We found that a H+ microdomain 0.3 μm in diameter forms around GFP.AE1 during physiological HCO3− transport. Carbonic anhydrase isoform II inhibition prevented H+ microdomain formation. We also measured the rate of H+ movement from PM GFP.AE1 to endoplasmic reticulum (ER), using mNect fused to the cytosolic face of ER-resident calnexin (CNX.mNect). The rate of H+ diffusion through cytosol was 60-fold faster than along the cytosolic surface of the plasma membrane. The pH environment surrounding pH regulatory transport proteins may differ as a result of H+ microdomain formation, which will affect nearby pH-sensitive processes.

Seasonal and long-term changes in pH in the Dutch coastal zone

Abstract. Recent observations and modelling studies suggest that biogeochemical changes can mask atmospheric CO2-induced pH decreases. Data collected by the Dutch monitoring authorities in different coastal systems (North Sea, Wadden Sea, Ems-Dollard, Eastern Scheldt and Scheldt estuary) since 1975 provide an excellent opportunity to test whether this is the case in the Dutch coastal zone. The time-series were analysed using Multi-Resolution Analysis (MRA) which resulted in the identification of system-dependent patterns on both seasonal and intra-annual time scales. The observed rates of pH change greatly exceed those expected from enhanced CO2 uptake, thus suggesting that other biogeochemical processes, possibly related to changes in nutrient loading, can play a dominant role in ocean acidification.

Equilibration Reaction from Single Addition of Base to Determine Soil Lime Requirement

The University of Georgia Soil, Plant, and Water Laboratory (SPW) uses a single‐addition titration for estimating soil lime requirement. The lime requirement depends in part on a soil's pH buffering capacity (described as lime buffer capacity [LBC] in mg CaCO3 kg−1 per pH unit), which is estimated from the rise in soil pH after Ca(OH)2 is added and allowed to react for 30 min. The 30‐min reaction time has not been sufficient to reach equilibrium between the soil and Ca(OH)2, resulting in an underestimation of the LBC. As a corrective measure, the SPW adjusts the agricultural lime recommendations to account for the lack of equilibrium. This study investigated the rate of pH change after Ca(OH)2 is added to acid soils. Specifically, the objectives of this study were to: (i) determine the time in which the Ca(OH)2–treated samples reached pH equilibrium; and (ii) determine if a relationship exists between the LBC estimated from a 30‐min equilibration and the LBC estimated from the time in which the sample had reached an equilibrium pH. The 25 soils used in this study were equilibrated for up to 96 h. Results indicated that the soils had reached an equilibrium pH by 84 h after the addition of Ca(OH)2 The ratio (mean of 84‐ and 96‐h LBC/30‐min LBC) could be predicted with the equation 1.4742 + 0.0023(30‐min LBC) (r2 = 0.82). This relationship allows the current titration procedure with 30‐min equilibration time to be used to predict the equilibrium LBC, which in turn can be used to calculate more accurate lime recommendations.

Rapidly changing ocean pH and the increasing transparency of the ocean to sound.

The intrinsic sound absorption coefficient (á, dB/km) of seawater is pH dependent with significant effects at 10 kHz and below. Ocean pH is declining from fossil fuel CO2 invasion, from excess nutrient input, and from climate change reducing ocean ventilation. These effects produce reductions in ocean borate and carbonate species such that an ∼18% decrease in á in the upper ocean has occurred today. Reasonable projections based on IPCC scenarios predict changes of 40% or more by mid-century [Hester et al., Geophys. Res. Lett. 35, L19601 (2008)]; larger changes in the sound channel are very likely. The projected increased transparency of the ocean to sound has attracted strong international environmental attention, and also provides an opportunity for acoustic detection and monitoring of such changes over large ocean regions. How strong is the basis for such assertions, can they be tested, and how well can environmental effects be predicted? This tutorial shows that the rate of change in pH in the sound channel has been underestimated, and how the unusual 1970s era reliance on the Soviet Gorshkov atlas as a pH data resource came about. This now presents a challenge for convergence of modern acoustic, environmental, and global change needs.

Role of 20-kDa Amelogenin (P148) Phosphorylation in Calcium Phosphate Formation in Vitro

The potential role of amelogenin phosphorylation in enamel formation is elucidated through in vitro mineralization studies. Studies focused on the native 20-kDa porcine amelogenin proteolytic cleavage product P148 that is prominent in developing enamel. Experimental conditions supported spontaneous calcium phosphate precipitation with the initial formation of amorphous calcium phosphate (ACP). In the absence of protein, ACP was found to undergo relatively rapid transformation to randomly oriented plate-like apatitic crystals. In the presence of non-phosphorylated recombinant full-length amelogenin, rP172, a longer induction period was observed during which relatively small ACP nanoparticles were transiently stabilized. In the presence of rP172, these nanoparticles were found to align to form linear needle-like particles that subsequently transformed and organized into parallel arrays of apatitic needle-like crystals. In sharp contrast to these findings, P148, with a single phosphate group on serine 16, was found to inhibit calcium phosphate precipitation and stabilize ACP formation for more than 1 day. Additional studies using non-phosphorylated recombinant (rP147) and partially dephosphorylated forms of P148 (dephoso-P148) showed that the single phosphate group in P148 was responsible for the profound effect on mineral formation in vitro. The present study has provided, for the first time, evidence suggesting that the native proteolytic cleavage product P148 may have an important functional role in regulating mineralization during enamel formation by preventing unwanted mineral formation within the enamel matrix during the secretory stage of amelogenesis. Results obtained have also provided new insights into the functional role of the highly conserved hydrophilic C terminus found in full-length amelogenin.

S1091 A New Method for Determining Gastric Acid Output Using a Wireless Capsule

of PPIs on physiological parameters of the UGI tract. Methods:20 healthy subjects (12M/ 8F,mean 42 yrs,range 22-74) were treated with esomeprazole 40mg bid for one week (last dose taken 1h before SP ingestion). Another 50 healthy subjects (31M/19F,mean 36 yrs,range 18-64) underwent evaluation in absence of PPIs. All subjects underwent SP test after ingesting a SmartBar mealTM+120cc water. We searched for a rapid luminal pH rise (>0.5pH-units) that was sustained to potentially mark exit of SP from stomach. An abd x-ray(KUB) was taken to confirm passage from stomach. Parameters analyzed were:pH difference at GET, rate of pH change(slope:pH-units/sec) at GET, mean gastric pH 30min before GET, small bowel transit time (SBTT), frequency of contractions (Ct) and pressure area under the curve (AUC) 20min before/after GET. Results:GET was identified in 100% of 20 subjects treated with PPIs. Mean luminal pH increase at GET was 1.1 pH-units with mean pH slope=0.15pHunits/sec. The pH in all cases rose >0.6 pH-units with corresponding increase in gastric pressures signifying GET and exit was confirmed with KUB. There was no difference in GET or SBTT between PPI subjects v. non-PPI subjects. PPI subjects had a higher mean baseline gastric pH before GET than non-PPI subjects but pH at GET was similar. There was no difference in Ct/AUC before GET. After GET, PPI subjects had more Ct than nonPPI subjects but there was no difference in AUC. Conclusion:PPI therapy reduced the magnitude of pH change which marked passage of SP from stomach. However, using modified criteria with a sustained sudden pH rise of >0.6 pH-units, SP was able to measure GET in all patients taking PPI 2x/day. PPIs increased duodenal contractility in the 20 minutes after GET perhaps from changes in acid milieu of proximal duodenum.

DETERMINATION OF pH CHANGE KINETICS DURING DIFFERENT STAGES OF KASHAR CHEESE MANUFACTURING FROM RAW AND PASTEURIZED MILK WITH ADDITION OF THERMOPHILIC, MESOPHILIC AND MIXED THERMOPHILIC CULTURE

ABSTRACT The pH change kinetics during Kashar cheese production from raw and pasteurized milk with addition of thermophilic, mesophilic and mixed thermophilic‐mesophilic lactic acid bacteria were evaluated. The kinetics of pH change were determined during milk ripening, cooking/holding and pressing/fermentation phases of Kashar cheese. The pH decreased logarithmically, nonlinearly, with time in the milk ripening period, and reduced linearly with time in the cooking/holding and pressing/fermentation stages. Pasteurization of milk retarded the rate of change in pH during the three periods. The highest rate of pH change was determined in the addition of thermophilic culture, followed by mixed thermophilic‐mesophilic and then mesophilic ones during milk ripening. The pH change characteristics of cheese made with thermophilic starter were similar to the cheese made with mixed thermophilic‐mesophilic culture, but different from mesophilic lactic acid bacteria during cooking/holding and pressing/fermentation stages. PRACTICAL APPLICATIONSOne of the important factors in the control of cheese quality is the extent of acid production in the vat. Acid development at a desired rate is important during cheese making. The progress of acidification is monitored by pH change in the industrial Kashar cheese production. Three main stages have been recognized with respect to pH change: milk ripening, cooking/holding and pressing/fermentation. This study evaluated and compared the pH change kinetics during various stages of Kashar cheese making using raw, pasteurized milk with the addition of thermophilic, mesophilic and mixed thermophilic culture. This work may help in the comparison of raw and pasteurized milk, and in the selection of appropriate starter culture for Kashar cheese production.

Extremely alkaline intracellular pH in the anterior stomach of larval yellow fever mosquitoes (Aedes aegypti)

The anterior stomach of larval Aedes aegypti is an alkalinizing organ where basolateral V‐ATPase drives luminal alkalinization to a pH of up to 12. However, the apical mechanisms involved are unknown. We hypothesized that luminal alkalinization involves absorption of H+ via apical H+ channels. Such a system would require increased intracellular pH (pHi) to function effectively. pHi was monitored using live cell imaging and BCECF as a pH‐dependent fluorophore. Serotonin (0.2 ìM), which stimulates luminal alkalinization, increased pHi in the anterior stomach from 7.0 ± 0.1 to 7.7 ± 0.1 (N = 64), whereas pHi was not affected in the posterior stomach (6.7 ± 0.1 before and 6.8 ± 0.1 after serotonin; N = 19). Perfusing the lumen with pH 10 saline increased pHi to 8.6 ± 0.1 (N = 41), suggesting a marked apical H+ permeability. However, in presence of luminal Zn2+ (10 ìM) similarly high pHi values were recorded (8.2 ± 0.1; N = 15), indicating that an apical proton channel, if present at all, cannot be blocked with Zn2+. The rate of pH change after switching to pH 10 in the lumen in the presence or absence of luminal Zn2+ was also not different. Together these results show that remarkably alkaline pHi values can be observed in the anterior stomach of larval Aedes aegypti. However, further investigation is required to determine the transporters involved in this unique physiological system. This work was supported by NIH (1R01AI063463‐01A2).

Direct Experimental Evidence for a Heterogeneous Reaction of Ozone with Bromide at the Air−Aqueous Interface

Recent experimental and theoretical evidence has indicated an enhancement of the heavier halide ions at the air-aqueous interface, relative to their bulk concentrations. This, along with an order of magnitude discrepancy between measured and predicted Br2 production in the reaction of ozone with deliquesced NaBr aerosol, has led to the suggestion that an interface reaction occurs between ozone and bromide. We have used harmine, a beta-carboline alkaloid, as an interface-sensitive fluorescent pH probe in order to measure pH changes associated with the interfacial reaction of ozone and bromide. The rate of pH change depends upon the bulk bromide concentration in a way which is well described by a Langmuir-Hinshelwood kinetic model. In the presence of octanol at the interface, the rate of pH change tracks the octanol adsorption isotherm, as expected if octanol enhances the concentration of ozone at the surface.

MODELING LIME REACTION IN PEAT-BASED SUBSTRATES

Limestone is incorporated into peat-based substrates to neutralize substrate acidity, increase pH buffering capacity, and provide calcium and magnesium. Limestones differ in their rate of pH change, equilibrium pH, and proportion of unreacted “residual” lime. In horticulture, lime reactivity is currently measured empirically in batch tests whereby limestone is incorporated into a batch of substrate and pH change is measured over time. Our objective was to develop a quantitative model to describe reaction of lime over time. The lime reaction model predicts the substrate-pH based on lime acid neutralizing capacity, lime type (calcitic, dolomitic, or hydrated), lime particle size distribution, application concentration, and the nonlimed pH and neutralizing requirement (buffering) of the substrate. Residual lime is calculated as the proportion of lime remaining following gradual neutralization of the substrate acidity (by subtraction of reacted lime from total applied lime).

(66) Modeling Lime Reaction in Horticultural Substrates

Limestone is incorporated into horticultural substrates to neutralize substrate acidity, increase pH buffering capacity, and provide calcium and magnesium. Limestones differ in their rate of pH change, equilibrium pH, and proportion of unreacted “residual”? lime. In horticulture, lime reactivity is currently measured empirically in batch tests, whereby limestone is incorporated into a batch of substrate and pH change is measured over time. Our objective was to develop a quantitative model to describe reaction of lime over time. The lime reaction model predicts the substrate-pH based on lime acid neutralizing capacity, lime type (calcitic, dolomitic, or hydrated), lime particle size distribution, application concentration, and the non-limed pH and neutralizing requirement (buffering) of the substrate. Residual lime is calculated as the proportion of lime remaining following gradual neutralization of the substrate acidity (by subtraction of reacted lime from total applied lime).

Induction plasma-sprayed photocatalytically active titania coatings and their characterisation by micro-Raman spectroscopy

Undoped TiO 2 (anatase) powder was deposited by induction plasma spraying (IPS) varying the plasma power, the carrier gas (argon) flow rate and the powder feed rate according to statistical design of experiments (SDE) methodology. In addition, anatase powders doped with varying amounts of V, Nb or Ta oxides were deposited by suspension plasma spraying (SPS) using reactive induction plasma spray (IPS) technology. The microstructure, crystallinity and anatase–rutile ratio of the coatings were studied by surface mapping with micro-Raman scanning spectroscopy and grazing-incidence X-ray diffraction (GIXD), and their photocatalytic activity was tested utilising the photocatalytic decomposition reaction of 4-chlorophenol in aqueous solution under UV irradiation. The rates of pH change (− dpH / d t) were compared with those of standard Degussa P-25 coatings. It was found that the photocatalytic activity of the samples showed a reasonable correlation with the phase content and the plasma processing conditions. In particular, the activity of coatings doped with 4 at.% of either Nb or Ta exceeded those of standard Degussa P-25 coatings.

Transport Activity of MCT1 Expressed in Xenopus Oocytes Is Increased by Interaction with Carbonic Anhydrase

Injection of carbonic anhydrase isoform II (CA) into Xenopus frog oocytes increased the rate of H+ flux via the rat monocarboxylate transporter isoform 1 (MCT1) expressed in the oocytes. MCT1 activity was assessed by changes of intracellular H+ concentration measured by pH-selective microelectrodes during application of lactate. CA-induced augmentation of the rate of H+ flux mediated by MCT1 was not inhibited by ethoxyzolamide (10 microM) and did not depend on the presence of added CO2/HCO3- but was suppressed by injection of an antibody against CA. Deleting the C terminus of the MCT1 greatly reduced its transport rate and removed transport facilitation by CA. Injected CA accelerated the CO2/HCO3(-)-induced acidification severalfold, which was blocked by ethoxyzolamide and was independent of MCT1 expression. Mass spectrometry confirmed activity of CA as injected into the frog oocytes. With pulldown assays we demonstrated a specific binding of CA to MCT1 that was not attributed to the C terminus of MCT1. Our results suggest that CA enhances MCT1 transport activity, independent of its enzymatic reaction center, presumably by binding to MCT1.

Platelet indices as quality markers of platelet concentrates during storage.

The quality of platelet concentrates (PC) is an important issue in transfusion therapy. Recently, platelet indices have been used as markers for the quality control of PCs, as these reflect storage-induced shape changes in platelets. We also analyzed platelet indices such as platelet count, which could be detrimental and influence the rate of pH change during acceptable storage conditions. In the present study, platelet indices (with and without EDTA) were analyzed in stored PC. Forty pooled PRP-PCs were stored for 7 days and various platelet indices were analyzed with and without EDTA incubation. These indices included platelet count (PLT), mean platelet volume (MPV), platelet distribution width (PDW) and platelet large cell ratio (PLCR). Difference in platelet paramters dPLT, dMPV, dPDW and dPLCR were calculated. Platelet indices correlating with pH changes, as determined by regression analysis, included dMPV and dPDW, while dPLT did not show much correlation (P < 0.05). Mean pH decreased from 7.25 to 6.86 between day 0 and day 7, respectively (P > 0.05). Platelet indices correlating with pH included PDW and MPV, while PLT did not show much correlation with pH. The platelet index dPDW (r = -0.26) and dMPV (r = -0.18) showed maximum, but not perfect, correlation with pH (P < 0.01). The coefficient of determination (R2) was maximum for the platelet indices dPDW and dP-LCR (R2 > 0.6). We conclude that measurements of platelet indices after EDTA incubation have great potential as quality markers of PC, especially when analyzed in combination with pH.

Evaluation of pH change kinetics during various stages of Cheddar cheese-making from raw, pasteurized, micro-filtered and high-pressure-treated milk

The change in pH during Cheddar cheese-making is largely determined by the buffering capacity of milk, curd and/or whey, and is moderated by the presence of inhibitors and treatment of milk prior to cheese-making. The pH change kinetics during Cheddar cheese-making starting from raw, heat-treated, micro-filtered (MF), and high-pressure (HP)-treated milks were evaluated. Heat treatment and micro-filtration were equivalent of achieving commercial pasteurization of milk. High-pressure treatment included two pressure levels and two treatment times (300 MPa for 60 and 90 min and 400 MPa for 32 and 40 min), calculated to be equivalent to achieve 4 and 6 decimal reductions of Listeria monocytogenes counts. Kinetics of pH change were evaluated during three stages of the Cheddar cheese-making process—milk ripening, cooking/holding and cheddaring. The influences of different treatments on pH change were somewhat different in the three phases studied. The pH decreased linearly with time during the first two stages and decreased logarithmically with time in the cheddaring phase. As compared to the ripening of untreated raw milk, all other treatments retarded the rate of change in pH with the micro-filtration having the lowest rate. During the cooking/holding stage, pasteurized and MF milks slightly enhanced the rate of pH change, while HP-treated milks continued the slower rate. During the final stage (cheddaring), the rate of change in pH with the HP-treated milks was about the same as in MF milk; however, both delayed the rate relative to raw and heat-pasteurized milks.

How Helicobacter pylori urease may affect external pH and influence growth and motility in the mucus environment: evidence from in-vitro studies.

Survival of Helicobacter pylori is dependent upon urease in the cytoplasm and at the bacterial surface. We have sought to clarify how alkaline ammonium salts, released from urea by this enzyme, might alter mucus pH and so affect growth and motility of the bacterium in the gastric mucus environment. Experiments were conducted in vitro to determine how the growth and motility of H. pylori are affected by changes in external pH, and how the bacterium, by hydrolysing urea, alters the pH of the bicarbonate buffer that occurs at the gastric mucosal surface. These data were fitted into experimental models that describe how pH varies within the mucus layer in the acid-secreting stomach. H. pylori was motile between pH 5 and 8, with optimal motility at pH 5. It grew between pH 6 and 8, with optimal growth at pH 6. The bacterium had urease activity between pH 2.7 and 7.4, as evidenced by pH rises in bicarbonate-buffered solutions of urea. Changes in buffer pH were dependent upon initial pH and urea concentration, with the greatest rate of pH change occurring at pH 3. Modelling experiments utilizing these data indicated that (1) in the absence of urease, H. pylori growth and motility in the mucus layer would be restricted severely by low mucus pH in the acid-secreting stomach, and (2) urease will sometimes inhibit H. pylori growth and motility in the mucus layer by elevating the pH of the mucus environment above pH 8. Urease is essential to the growth and motility of H. pylori in the mucus layer in the acid-secreting stomach, but, paradoxically, sometimes it might suppress colonization by raising the mucus pH above 8. This latter effect may protect the bacteria from the adverse consequences of overpopulation.