Growth and aroma contribution of <Emphasis Type="Italic">Microbacterium foliorum</Emphasis>, <Emphasis Type="Italic">Proteus vulgaris</Emphasis> and <Emphasis Type="Italic">Psychrobacter</Emphasis> sp. during ripening in a cheese model medium

The growth and aroma contribution of Microbacterium foliorum, Proteus vulgaris and Psychrobacter sp., some common but rarely mentioned cheese bacteria, were investigated in a cheese model deacidified by Debaryomyces hansenii during the ripening process. Our results show that these bacteria had distinct growth and cheese flavour production patterns during the ripening process. P. vulgaris had the greatest capacity to produce not only the widest variety but also the highest quantities of volatile compounds with low olfactive thresholds, e.g. volatile sulphur compounds and branched-chain alcohols. Such compounds produced by P. vulgaris increased after 21 days of ripening and reached a maximum at 41 days. The three bacteria studied exhibited various degrees of caseinolytic, aminopeptidase and deaminase activities. Moreover, P. vulgaris had a greater capacity for hydrolysing casein and higher deaminase activity. Our results show that P. vulgaris, a Gram-negative bacterium naturally present on the surface of ripened cheeses, could produce high concentrations of flavour compounds from amino acid degradation during the ripening process. Its flavouring role in cheese cannot be neglected. Moreover, it could be a useful organism for producing natural flavours as dairy ingredients.     

Role of protein kinase C-delta in the age-dependent secretagogue action of bile acids in mammalian colon

The role of specific PKC isoforms in the regulation of epithelial Cl(-) secretion by Ca(2+)-dependent secretagogues remains controversial. In the developing rabbit distal colon, the bile acid taurodeoxycholate (TDC) acts via intracellular calcium to stimulate Cl(-) transport in adult, but not in young, animals, whereas the PKC activator phorbol dibutyrate (PDB) stimulates Cl(-) transport at all ages. We tested the hypothesis that specific PKC isoforms account for the age-specific effects of TDC. The effects of conventional (cPKC) and novel (nPKC) PKC-specific inhibitors on TDC- and PDB-stimulated Cl(-) transport in adult and weanling colonocytes were assessed by using 6-methoxy-quinolyl acetoethyl ester. In adult colonocytes, the cPKC inhibitor G?-6976 inhibited PDB action but not TDC action, whereas the cPKC and nPKC inhibitor G?-6850 blocked both TDC and PDB actions. Additionally, rottlerin and the PKC-delta-specific inhibitor peptide (deltaV1-1) inhibited TDC- and PDB-stimulated Cl(-) transport in adult colonocytes. Rottlerin also decreased TDC-stimulated short-circuit current in intact colonic epithelia. Only G?-6976, but neither rottlerin nor deltaV1-1, inhibited PDB-stimulated transport in weanling colonocytes. Colonic lysates express PKC-alpha, -lambda, and -iota protein equally at all ages, but they do not express PKC-gamma or -theta at any age. Expression of PKC-beta and PKC-epsilon protein was newborn>adult>weanling, whereas PKC-delta was expressed in adult but not in weanling or newborn colonocytes. TDC (1.6-fold) and PDB (2.0-fold) stimulated PKC-delta enzymatic activity in adult colonocytes but failed to do so in weanling colonocytes. PKC-delta mRNA expression showed age dependence. Thus PKC-delta appears critical for the action of TDC in the adult colon, and its low expression in young animals may account for their inability to secrete in response to bile acids.     

Effect of solid-state buffers on the catalytic activity of papain in low water media

The catalytic activity of papain in the synthesis of Z-Gly-Phe-NH₂ in tert-butanol has been studied in the presence of solid-state acid–base buffers (acids and their sodium salts). All buffer pairs tested reduced the reaction rate compared with the control, particularly the most acidic and basic (assessed by either aqueous pK_a or the response of an organic phase indicator). The highest rates, close to the control, were found with glutamic acid/glutamate-Na, PIPES/PIPES-Na and NaH₂PO₄/Na₂HPO₄. However, these pairs were unable to erase the pH memory phenomenon, or to overcome the effect of spiking with acetic acid. Hence, at least these buffers do not seem to be able to affect the protonation state and catalytic activity of papain. In the last aqueous solution before drying, the presence of activating agents (cysteine plus EDTA) was more important than buffer ions.     

Inhibitory effects of choleretic hydroxyacetophenones on ileal bile acid transport in rats

The effects of the choleretic and cholesterol lowering compound, 2,4,6-trihydroxyacetophenone (THA) and its analog, 2,6-dihydroxyacetophenone (DHA), on ileal bile acid absorption were investigated in rats. THA inhibited taurocholate (TC) uptake into ileal brush-border membrane vesicles (BBMV), showing a maximum inhibition of 50%, whereas DHA completely inhibited TC uptake into ileal BBMV. THA exhibited competitive inhibition with a Ki of 9.88 mM, while DHA showed non-competitive inhibition with a Ki of 7.65 mM. Both total and ouabain-sensitive basolateral membrane (BLM) Na+-K+-ATPase activities, which are essential for maintenance of the Na+-gradient for bile acid transport, were inhibited by THA and DHA in a dose-dependent manner. The inhibition of BLM ATPase was uncompetitive with a Ki of 10.1 and 5.0 mM for THA and DHA, respectively. Administration of THA or DHA (400 micromol/kg) twice a day, to hypercholesterolemic rats for 3 weeks caused similar and marked reductions in plasma cholesterol to 60% of the cholesterol-fed controls. The data suggest that the inhibitory actions of THA and DHA on two essential components of ileal bile acid recycling to liver could, in part, contribute to the cholesterol lowering effect of the hydroxyacetophenone compounds. These effects on decreasing bile acid recycling, in combination with their potent choleretic effect, accelerating biliary excretion of bile acids, are responsible for the effective cholesterol lowering capacities of these compounds.     

Molecular Monitoring of Microbial Population Dynamics During Operational Periods of Anaerobic Hybrid Reactor Treating Cassava Starch Wastewater

This study characterized the microbial community and population dynamics in an anaerobic hybrid reactor (AHR) treating cassava starch wastewater. Methanogens and nonmethanogens were followed during the start-up and operation of the reactor, and linked to operational and performance data. Biomass samples taken from the sludge bed and packed bed zones of the AHR at intervals throughout the operational period were examined by 16S rRNA fluorescence in situ hybridization (FISH). The start-up seed and the reactor biomass were sampled during the feeding of the wastewater with a chemical oxygen demand (COD) value of 8 g L⁻¹ and a hydraulic retention time (HRT) of 8 days. These samples were characterized by the predominance of cells with long-rod morphology similar to Methanosaeta spp. Following a sharp operational change, accomplished by increasing the COD concentration of the organic influent from 8 to 10 g L⁻¹ and reducing the HRT from 8 to 5 days, there was a doubling of the organic loading rate, a reduction of the COD removal efficiency, as well as decreased methane content in the biogas and an accumulation of total volatile acids in the reactor. Moreover, this operational change resulted in a significant population shift from long-rod Methanosaeta-like cells to tetrad-forming Methanosarcina-like cells. The distributions of microbial populations involved in different zones of the AHR were determined. The results showed that nonmethanogens became the predominant population in both sludge and the packed bed zone. However, the percentage of methanogens in the packed bed zone was higher than that in the sludge bed zone. This higher percentage of methanogens was likely caused by the fact that the packed bed zone provided a suitable environmental condition with an appropriate nutrient availability for methanogen growth.     

Production of volatile aroma compounds by bacterial strains isolated from different surface-ripened French cheeses

Twelve bacterial strains belonging to eight taxonomic groups: Brevibacterium linens, Microbacterium foliorum, Arthrobacter arilaitensis, Staphylococcus cohnii, Staphylococcus equorum, Brachybacterium sp., Proteus vulgaris and Psychrobacter sp., isolated from different surface-ripened French cheeses, were investigated for their abilities to generate volatile aroma compounds. Out of 104 volatile compounds, 54 volatile compounds (identified using dynamic headspace technique coupled with gas chromatography-mass spectrometry [GC-MS]) appeared to be produced by the different bacteria on a casamino acid medium. Four out of eight species used in this study: B. linens, M. foliorum, P. vulgaris and Psychrobacter sp. showed a high flavouring potential. Among these four bacterial species, P. vulgaris had the greatest capacity to produce not only the widest varieties but also the highest quantities of volatile compounds having low olfactive thresholds such as sulphur compounds. Branched aldehydes, alcohols and esters were produced in large amounts by P. vulgaris and Psychrobacter sp. showing their capacity to breakdown the branched amino acids. This investigation shows that some common but rarely mentioned bacteria present on the surface of ripened cheeses could play a major role in cheese flavour formation and could be used to produce cheese flavours.     

Periodic synchronisation of dengue epidemics in Thailand over the last 5 decades driven by temperature and immunity

The spatial distribution of dengue and its vectors (spp. Aedes) may be the widest it has ever been, and projections suggest that climate change may allow the expansion to continue. However, less work has been done to understand how climate variability and change affects dengue in regions where the pathogen is already endemic. In these areas, the waxing and waning of immunity has a large impact on temporal dynamics of cases of dengue haemorrhagic fever. Here, we use 51 years of data across 72 provinces and characterise spatiotemporal patterns of dengue in Thailand, where dengue has caused almost 1.5 million cases over the last 30 years, and examine the roles played by temperature and dynamics of immunity in giving rise to those patterns. We find that timescales of multiannual oscillations in dengue vary in space and time and uncover an interesting spatial phenomenon: Thailand has experienced multiple, periodic synchronisation events. We show that although patterns in synchrony of dengue are similar to those observed in temperature, the relationship between the two is most consistent during synchronous periods, while during asynchronous periods, temperature plays a less prominent role. With simulations from temperature-driven models, we explore how dynamics of immunity interact with temperature to produce the observed patterns in synchrony. The simulations produced patterns in synchrony that were similar to observations, supporting an important role of immunity. We demonstrate that multiannual oscillations produced by immunity can lead to asynchronous dynamics and that synchrony in temperature can then synchronise these dengue dynamics. At higher mean temperatures, immune dynamics can be more predominant, and dengue dynamics more insensitive to multiannual fluctuations in temperature, suggesting that with rising mean temperatures, dengue dynamics may become increasingly asynchronous. These findings can help underpin predictions of disease patterns as global temperatures rise.

This study shows that spatially large-scale shifts in temperature can synchronize dengue dynamics across Thailand; however, as average temperatures rise, dengue dynamics may increasingly be dictated by dynamics of immunity, which may in turn mean fewer synchronous outbreaks in the future.