The quorum-sensing molecule 2-phenylethanol impaired conidial germination, hyphal membrane integrity and growth of Penicillium expansum and Penicillium nordicum

AIMS

The aim of the study was to investigate the antifungal effects of a quorum sensing-molecule, 2-phenylethanol, against the food spoilage moulds Penicillium expansum and Penicillium nordicum.

METHODS AND RESULTS

Conidial germination of the tested Penicillium spp. (three strains in total) were inhibited by treatments with 2-phenylethanol in a concentration-dependent manner. Germinated conidia was significantly reduced from 4·4-16·7% at 7·5 mmol l^-1 and completely inhibited at 15 mmol l^-1 2-phenylethanol. Integrity of conidial cell membranes was unaffected by 2-phenylethanol resulting in reversible inhibition pattern of germination. In contrast, membrane permeability of actively growing hyphae was severely compromised, showing 63·5 - 75·7% membrane damage upon treatment with 15 mmol l^-1 2-phenylethanol. The overall inhibitory effect of 2-phenylethanol on colony development and growth of P. expansum and P. nordicum was additionally confirmed.

CONCLUSIONS

2-phenylethanol inhibits conidial germination and growth of P. expansum and P. nordicum in a nonlethal, reversible and concentration-dependent manner.

SIGNIFICANCE AND IMPACT OF THE STUDY

The study indicates that 2-phenylethanol can find potential application as an antifungal agent for biological control of moulds in the food industry.

Non-Saccharomyces yeasts protect against epithelial cell barrier disruption induced by Salmonella enterica subsp. enterica serovar Typhimurium

The human gastrointestinal epithelium makes up the largest barrier separating the body from the external environment. Whereas invasive pathogens cause epithelial barrier disruption, probiotic micro-organisms modulate tight junction regulation and improve epithelial barrier function. In addition, probiotic strains may be able to reduce epithelial barrier disruption caused by pathogenic species. The aim of this study was to explore non-Saccharomyces yeast modulation of epithelial cell barrier function in vitro. Benchmarking against established probiotic strains, we evaluated the ability of four nonpathogenic yeast species to modulate transepithelial electrical resistance (TER) across a monolayer of differentiated human colonocytes (Caco-2 cells). Further, we assessed yeast modulation of a Salmonella Typhimurium-induced epithelial cell barrier function insult. Our findings demonstrate distinct patterns of non-Saccharomyces yeast modulation of epithelial cell barrier function. While the established probiotic yeast Saccharomyces boulardii increased TER across a Caco-2 monolayer by 30%, Kluyveromyces marxianus exhibited significantly stronger properties of TER enhancement (50% TER increase). In addition, our data demonstrate significant yeast-mediated modulation of Salmonella-induced epithelial cell barrier disruption and identify K. marxianus and Metschnikowia gruessii as two non-Saccharomyces yeasts capable of protecting human epithelial cells from pathogen invasion.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study demonstrates distinct patterns of non-Saccharomyces yeast modulation of epithelial cell barrier function in vitro. Further, our data demonstrate significant yeast-mediated modulation of Salmonella Typhimurium-induced epithelial cell barrier disruption and identify Kluyveromyces marxianus and Metschnikowia gruessii as two non-Saccharomyces yeasts capable of protecting human epithelial cells from pathogen invasion. This study is the first to demonstrate significant non-Saccharomyces yeast-mediated epithelial cell barrier protection from Salmonella invasion, thus encouraging future efforts aimed at confirming the observed effects in vivo and driving further strain development towards novel yeast probiotics.

Ammonia production and its possible role as a mediator of communication for Debaryomyces hansenii and other cheese-relevant yeast species

Ammonia production by yeasts may contribute to an increase in pH during the ripening of surface-ripened cheeses. The increase in pH has a stimulatory effect on the growth of secondary bacterial flora. Ammonia production of single colonies of Debaryomyces hansenii, Saccharomyces cerevisiae, Yarrowia lipolytica, and Geotrichum candidum was determined on glycerol medium (GM) agar and cheese agar. The ammonia production was found to vary, especially among yeast species, but also within strains of D. hansenii. In addition, variations in ammonia production were found between GM agar and cheese agar. Ammonia production was positively correlated to pH measured around colonies, which suggests ammonia production as an additional technological parameter for selection of secondary starter cultures for cheese ripening. Furthermore, ammonia appeared to act as a signaling molecule in D. hansenii as reported for other yeasts. On GM agar and cheese agar, D. hansenii showed ammonia production oriented toward neighboring colonies when colonies were grown close to other colonies of the same species; however, the time to oriented ammonia production differed among strains and media. In addition, an increase of ammonia production was determined for double colonies compared with single colonies of D. hansenii on GM agar. In general, similar levels of ammonia production were determined for both single and double colonies of D. hansenii on cheese agar.

Identification of amino acids involved in the Flo11p-mediated adhesion of Saccharomyces cerevisiae to a polystyrene surface using phage display with competitive elution

AIMS

To identify the main amino acids involved in the Flo11p-mediated adhesion of Saccharomyces cerevisiae to the polystyrene surface PolySorp.

METHODS AND RESULTS

Using a combination of phage display and competitive elution revealed that 12-mer peptides of phages from competitive panning with S. cerevisiae FLO11 wild-type (TBR1) cells had a higher consensus than those from competitive panning with S. cerevisiae flo11Delta mutant (TBR5) cells, suggesting that the wild-type cells interact with the plastic surface in a stronger and more similar way than the mutant cells. Tryptophan and proline were more abundant in the peptides of phages from competitive elution with FLO11 cells than in those from competitive elution with flo11Delta cells. Furthermore, two phages with hydrophobic peptides containing 1 or 2 tryptophan, and 3 or 5 proline, residues inhibited the adhesion of FLO11 cells to PolySorp more than a phage with a hydrophobic peptide containing no tryptophan and only two proline residues.

CONCLUSIONS

Our results suggest a key role of tryptophan and proline in the hydrophobic interactions between Flo11p on the S. cerevisiae cell surface and the PolySorp surface.

SIGNIFICANCE AND IMPACT OF THE STUDY

Our study may contribute to the development of novel strategies to limit yeast infections in hospitals and other medical environments.

Lactic acid bacteria and yeasts associated with gowé production from sorghum in Bénin

AIMS

To identify the dominant micro-organisms involved in the production of gowé, a fermented beverage, and to select the most appropriate species for starter culture development.

METHODS AND RESULTS

Samples of sorghum gowé produced twice at three different production sites were taken at different fermentation times. DNA amplification by internal transcribed spacer-polymerase chain reaction of 288 lactic acid bacteria (LAB) isolates and 16S rRNA gene sequencing of selected strains revealed that the dominant LAB responsible for gowé fermentation were Lactobacillus fermentum, Weissella confusa, Lactobacillus mucosae, Pediococcus acidilactici, Pediococcus pentosaceus and Weissella kimchii. DNA from 200 strains of yeasts was amplified and the D1/D2 domain of the 26S rRNA gene was sequenced for selected isolates, revealing that the yeasts species were Kluyveromyces marxianus, Pichia anomala, Candida krusei and Candida tropicalis.

CONCLUSIONS

Gowé processing is characterized by a mixed fermentation dominated by Lact. fermentum, W. confusa and Ped. acidilactici for the LAB and by K. marxianus, P. anomala and C. krusei for the yeasts.

SIGNIFICANCE AND IMPACT OF THE STUDY

The diversity of the LAB and yeasts identified offers new opportunities for technology upgrading and products development in gowé production. The identified species can be used as possible starter for a controlled fermentation of gowé.

Relationship between growth and pH gradients of individual cells of Debaryomyces hansenii as influenced by NaCl and solid substrate

AIMS

To examine the relationship between the growth and pH gradients of Debaryomyces hansenii at a single-cell level.

METHODS AND RESULTS

Using bioimaging techniques, the cell areas and early pH gradients (Delta pH(10)), i.e. the pH gradients determined 10 min after initiation of experiments, were determined for single cells of two D. hansenii strains in fluid and on solid (agar) substrate with and without 8% (w/v) NaCl. The combination of NaCl and solid substrate prolonged the growth initiation of both D. hansenii strains additively. In all our experiments, primarily two groups of cells existed; a vital group consisting of growing single cells with intact early pH gradients, and a group of dead cells without early pH gradients.

CONCLUSIONS

Our results show that growth initiation of the D. hansenii cells is severely affected by NaCl and to a lesser extent by the type of substrate in an additive and strain dependent way. Moreover, the early pH gradient of a vital D. hansenii cell cannot be correlated with the rate of its subsequent growth.

SIGNIFICANCE AND IMPACT OF THE STUDY

Our study reveals new knowledge on the growth and pH gradients of D. hansenii on solid surfaces in the presence of NaCl.

Antimicrobial activity of Bacillus subtilis and Bacillus pumilus during the fermentation of African locust bean (Parkia biglobosa) for Soumbala production

AIMS

To examine predominant isolates of Bacillus subtilis and B. pumilus isolated from Soumbala for their antimicrobial activity against indicator microorganisms as Micrococcus luteus, Staphyloccocus aureus, Bacillus cereus, Enterococus facium, Listeria monocytogenes, Escherichia coli, Salmonella typhimurium, Shigella dysenteriae, Yersinia enterocolitica, Aspergillus ochraceus and Penicillium roqueforti.

METHODS AND RESULTS

Growth inhibition of indicator microorganisms by cells and supernatants of three B. subtilis and two B. pumilus strains was investigated using agar diffusion tests. Inactivation of indicator microorganisms was investigated in laboratory broth and during the fermentation of African locust bean for Soumbala production. The Bacillus isolates showed variable ability of inhibition and inactivation according to the indicator microorganism. The supernatants of pure cultures of B. subtilis inhibited one strain of B. cereus, one of Staph. aureus and E. coli and caused abnormal germination of Aspergillus ochraceus. The supernatant of mixed cultures of B. subtilis and indicators inhibited all the indicators. A treatment with protease eliminated the inhibitions. Isolates of B. subtilis inactivated all the indicators organisms during the fermentation of African locust bean as well as in laboratory broth with about five to eight decimal reduction.

CONCLUSION

Bacillus isolates from Soumbala inhibit and inactivate Gram-positive and Gram-negative bacteria as well as ochratoxin A producing fungi during both laboratory cultivation and natural fermentation.

SIGNIFICANCE AND IMPACT OF THE STUDY

Selection of starter cultures of Bacillus spp. for controlled production of Soumbala.

Intracellular pH homeostasis plays a role in the NaCl tolerance of Debaryomyces hansenii strains

The effects of NaCl stress on cell area and intracellular pH (pHi) of individual cells of two Debaryomyces hansenii strains were investigated. Our results show that one of the strains was more NaCl tolerant than the other, as determined by the rate of growth initiation. Whereas NaCl stress caused similar cell shrinkages (30-35%), it caused different pHi changes of the two D. hansenii strains; i.e., in the more NaCl-tolerant strain, pHi homeostasis was maintained, whereas in the less NaCl-tolerant strain, intracellular acidification occurred. Thus, cell shrinkage could not explain the different intracellular acidifications in the two strains. Instead, we introduce the concept of yeasts having an intracellular pKa (pK(a,i)) value, since permeabilized D. hansenii cells had a very high buffer capacity at a certain pH. Our results demonstrate that the more NaCl-tolerant strain was better able to maintain its pK(a,i) close to its pHi homeostasis level during NaCl stress. In turn, these findings indicate that the closer a D. hansenii strain can keep its pK(a,i) to its pHi homeostasis level, the better it may manage NaCl stress. Furthermore, our results suggest that the NaCl-induced effects on pHi were mainly due to hyperosmotic stress and not ionic stress.

Yeast populations associated with Ghanaian cocoa fermentations analysed using denaturing gradient gel electrophoresis (DGGE)

The yeast populations associated with the fermentation of Ghanaian cocoa were investigated using denaturing gradient gel electrophoresis (DGGE). Samples were collected at 12-24 h intervals from heap and tray fermentations, at three different fermentation sites and different periods during the season. Eukaryotic universal primers were used to amplify a fragment of the 26S rRNA gene. The DGGE profiles were relatively complex, underlining that the fermentation of cocoa is a complex microbial process. The identities of selected fragments in the denaturing gels were revealed by sequencing. Hanseniaspora guilliermondii, Candida krusei and Pichia membranifaciens were detected from most fermentations, indicating their possible important role in the fermentation of Ghanaian cocoa. Saccharomyces cerevisiae and Candida zemplinina were almost exclusively detected during tray fermentations. The developed DGGE protocol was compared with traditional culture-based isolations. The results were comparable but slightly different, as one yeast species (C. zemplinina) was only detected using DGGE. On the other hand, Trichosporon asahii yielded only faint bands in the denaturing gels, despite the fact that it was detected using culture-based methods. Analysis of pure cultures showed that the targeted region of the 26S rRNA gene was poorly amplified in T. asahii, whereas all other investigated isolates were amplified efficiently using the chosen PCR approach. Cluster analysis revealed that the DGGE profiles clustered according to fermentation method and fermentation site. Furthermore, clustering according to progress in the fermentation was observed. The DGGE technique therefore seems to offer a relatively fast and reliable method for studying yeast population dynamics during cocoa fermentations.

Identification of genes and proteins induced during the lag and early exponential phase of lager brewing yeasts

AIMS

The aim of the present study is to identify genes and proteins whose expression is induced in lager brewing yeast during the lag phase and early exponential growth.

METHODS AND RESULTS

Two-dimensional gel electrophoresis was used to identify proteins induced during the lag and early exponential phase of lager brewing yeast in minimal medium. The identified, early-induced proteins were Ade17p, Eno2p, Ilv5gp, Sam1p, Rps21p and Ssa2p. For most of these proteins, the patterns of induction differed from those of the corresponding genes. However, the genes had similar early expression patterns in minimal medium as observed during lager brewing conditions. The expression of previously identified early-induced genes in Saccharomyces cerevisiae grown in minimal medium, ADO1, ALD6, ASC1, ERG4, GPP1, RPL25, SSB1 and YKL056C, was also early induced in lager yeast under brewing conditions.

CONCLUSIONS

The results indicate that the above-mentioned genes in general are induced during the lag phase and early exponential growth in Saccharomyces yeasts. The processes in which these genes take part are likely to play an important role during growth initiation.

SIGNIFICANCE AND IMPACT OF THE STUDY

Increased knowledge regarding the early growth phase of lager brewing yeast was obtained. Further, the universality of the identified expression patterns suggests new methodologies for optimization and control of growth initiation during brewing fermentations.

A flow cytometric technique for quantification and differentiation of bacteria in bulk tank milk

AIMS

The present study describes a flow cytometric technique for quantification and differentiation of bacteria in bulk tank milk according to the main cause of elevated counts.

METHODS AND RESULTS

A total of 75 Danish bulk tank milk samples exceeding the grading level of 3.0 x 10(4) CFU ml(-1) were examined by both flow cytometry and traditional microbiological analyses. The correlation coefficient (r) between the two methods was 0.71. For the differential analyses of the dominant bacterial populations four different parameters were used to give a species-characteristic pattern. The four parameters were as follows: staining with Oregon Green conjugated wheat germ agglutinin that binds to the cell wall of bacteria, staining with hexidium iodide that binds to all bacterial DNA, the flow cytometric forward scatter and the flow cytometric side scatter. Three regions in the flow cytometric plot were defined: region 1 includes bacteria mainly associated with poor hygiene, region 2 includes psychrotrophic hygiene bacteria and region 3 includes bacteria mainly related to mastitis. The ability of the flow cytometric technique to predict the main cause of elevated bacterial counts on routine samples was examined. Comparing these results with results obtained by traditional microbiological analyses for identification showed that for 81% of the samples the two techniques agreed on the main cause of an elevated bacterial count.

CONCLUSIONS

The ability of the presented flow cytometric technique to enumerate and differentiate bacteria in bulk tank milk according to the main cause of elevated counts was demonstrated.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study described the first step in development of a technique suitable for routine analyses of bulk tank milk samples. A technique indicating the main cause of an elevated count will enable the farmer to eliminate the contamination source within a short time limit.

Genetic diversity of the species Debaryomyces hansenii and the use of chromosome polymorphism for typing of strains isolated from surface-ripened cheeses

AIMS

To investigate the genetic diversity among strains of Debaryomyces hansenii and further to evaluate chromosome polymorphism determined by pulse-field gel electrophoresis (PFGE) as a tool for strain typing.

METHODS AND RESULTS

In total 56 isolates of D. hansenii were analysed by PFGE. The isolates included type strains and other strains obtained from culture collections as well as strains collected during production of Danish surface-ripened cheeses. By use of the PFGE technique the number and size of the chromosomal bands were calculated and the total genome size estimated. The number of chromosomal bands observed was found to vary from five to 10. The most common chromosome number was found to be six and for strains with six chromosomes the total genome size was found to vary from 9.4 to 12.6 Mb. The chromosome numbers for the type strain of each variety of D. hansenii (D. hansenii var. hansenii and D. hansenii var. fabryi) appeared to be six and seven respectively. By use of the PFGE technique it was possible to differentiate between all the investigated CBS strains and the vast majority of the dairy isolates. The dairy isolates that were found to have identical profiles (three of 56 isolates) were all isolated during production of one batch of surface-ripened cheeses and are likely to be the same strain isolated several times during cheese production. Further it was shown that the PFGE analysis did not result in a division of the two D. hansenii varieties, i.e. D. hansenii var. fabryi and D. hansenii var. hansenii into separate groups.

CONCLUSION

The present study shows that the chromosomal arrangement of D. hansenii strains is heterogenic and does have a distinct chromosome polymorphism. Further the PFGE technique was proved to have a high discriminative power for strain typing of D. hansenii.

SIGNIFICANCE AND IMPACT OF THE STUDY

The results obtained add to the first knowledge on the genetic diversity of the species D. hansenii. Further the distinct chromosome polymorphism of D. hansenii strains as shown in this study makes the PFGE technique a useful tool for strain typing of D. hansenii, e.g. during cheese production.

Lactic acid tolerance determined by measurement of intracellular pH of single cells of Candida krusei and Saccharomyces cerevisiae isolated from fermented maize dough

Strains of Candida krusei and Saccharomyces cerevisiae were grown together at 30 degrees C in MYGP broth, pH 2.5, in the presence of 106.4 mM undissociated lactic acid. The two C. krusei strains investigated grew within 48 h from initial counts of 2 x 10(4) to approximately 10(7) cells/ml whereas the two S. cerevisiae strains investigated survived but did not grow in the presence of 106.4 mM undissociated lactic acid at pH 2.5. To explain the differences in lactic acid tolerance of the two yeast species, we used fluorescence-ratio-imaging microscopy and a perfusion system to determine the short-term intracellular pH (pH(i)) changes in single cells of C. krusei and S. cerevisiae. The changes were investigated both in the presence of low (20.7 mM) and high (106.4 mM) concentrations of undissociated lactic acid. For both the investigated species 20.7 mM undissociated lactic acid did not seem to influence the initial pH(i) which for C. krusei was found to be approximately 8.0 and for S. cerevisiae 6.9-7.5. For both C. krusei strains, perfusion with 106.4 mM undissociated lactic acid induced only weak short-term pH(i) responses with a decrease in pH(i) of less than one pH unit. Contrary, for both strains of S. cerevisiae perfusion with 106.4 mM undissociated lactic acid resulted in a significant decrease in pH(i) from initially 6.9-7.5 to 6.2-6.4 after 1 min and further to a pH(i) of < or = 5.5 after 3 min after which it remained constant. The results obtained show that C. krusei is more resistant to short-term pH(i) changes caused by lactic acid than S. cerevisiae, and this, in turn, may be part of the explanation why C. krusei is more tolerant to lactic acid than S. cerevisiae.

Detection of resistance of lactic acid bacteria to a mixture of the hop analogue compounds tetrahydroiso-alpha-acids by noninvasive measurement of intracellular pH

AIMS

To examine the resistance of beer isolates of lactic acid bacteria (LAB) towards a mixture of tetrahydroiso-alpha-acids (Tetra) by growth experiments as well as by measurement of intracellular pH.

METHODS AND RESULTS

Beer LAB isolates were identified to species level by SDS-PAGE of whole-cell proteins. Beer isolates of Lactobacillus brevis showed better ability for growth in the presence of Tetra than nonbeer isolates of the L. brevis or other species of LAB including beer and nonbeer isolates. The antimicrobial effect of Tetra was also examined by noninvasive measurement of intracellular pH by fluorescence ratio imaging microscopy for selected beer isolates of L. brevis and Pediococcus inopinatus. Strains of L. brevis showing limited decrease of intracellular pH during exposure to Tetra also showed better ability for growth in the presence of these compounds as well as in commercial beer products.

CONCLUSIONS

It was possible to apply a method for noninvasive measurement of intracellular pH to predict the resistance of beer spoilage LAB towards the Tetra hop analogue compounds.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study demonstrated the usability of a new rapid method for detecting hop-resistant variants of known beer spoilage LAB species.

Predominant Microflora of Downgraded Danish Bulk Tank Milk

The microflora of downgraded Danish bulk tank milk was examined to identify the main causes of increased microbial counts. Seventy-five representative samples with a microbial count exceeding 3.0 x 10(4) cfu/mL were selected for a more detailed microbial examination. A total of 1237 isolates from these samples were identified. Gram-negative, oxidase-positive bacteria were found in 72% of the samples. Coliforms were found in 20% of the samples, and non-coliforms were found in 49% of the samples. Coryneforms, other gram-positive rods, Lactococcus spp., Micrococcus spp., and coagulase-negative Staphylococcus spp. were found in 28 to 53% of the samples. Bacillus spp., Enterococcus spp., Staphylococcus aureus, Streptococcus dysgalactiae, Streptococcus uberis, and yeasts were found in <25% of the samples. Additionally, the isolates were divided into 3 groups, based on the main cause of an elevated microbial count. Microorganisms primarily associated with poor hygiene dominated the microflora in 64% of the samples; bacteria also related to poor hygiene, but in addition associated with growth at low temperatures (psychrotrophic bacteria) dominated the microflora in 28% of the samples; and bacteria mainly associated with mastitis dominated the microflora in 8% of the samples. A bulk tank milk storage period of 48 h instead of 24 h did not affect the proportion of downgraded milk samples and could not be associated with a specific group of microorganisms. Further, no relationship was found between somatic cell counts and the presence of mastitis bacteria.

Microbial succession of Debaryomyces hansenii strains during the production of Danish surfaced-ripened cheeses

Surface-ripened cheeses of the Danbo type were analyzed for the presence of yeasts with special emphasis on Debaryomyces hansenii. Samples were taken from pasteurized milk, brine, and inoculation slurries and from cheese surfaces during ripening at a Danish dairy. D. hansenii was found to be the dominant yeast species throughout the ripening period, whereas other yeast species such as Trichosporon spp., Rhodotorula spp., and Candida spp. were found in minor concentrations during early stages of cheese ripening. Mitochondrial DNA RFLP was used to show that several strains of D. hansenii were present from the onset of ripening. Thereafter, a microbial succession among the strains took place during the ripening. After 3 d of ripening, only one strain was found. This particular strain was found to be dominant in 16 additional batches of surface-ripened cheeses. We investigated the cause of the observed microbial succession by determining the variation in strains with regard to their ability to grow on lactate and at different pH and NaCl concentrations. The strains were shown to vary in their ability to grow on lactate. In a full factorial design at three levels with factor levels close to the actual levels on the cheese surface, differences in pH and NaCl tolerances were observed. The dominant strain was found to be better adapted than other strains to the environmental conditions existing in surface-ripened cheeses during production [e.g., lactate as the main carbon source, pH 5.5 to 6.0 and NaCl concentrations of 7 to 10% (wt/vol)].

DNA typing methods for differentiation of Debaryomyces hansenii strains and other yeasts related to surface ripened cheeses

The discriminative power of ITS-PCR, ITS-PCR RFLP and mitochondrial (mt)-DNA RFLP were evaluated for differentiation of yeasts of importance for surface ripened cheeses. In total 60 isolates were included. Of these, 40 strains of the following species, Debaryomyces hansenii var. hansenii, D. hansenii var. fabryi, Saccharomyces cerevisiae, Candida zeylanoides, Kluyveromyces lactis and Yarrowia lipolytica, were obtained from culture collections and 20 isolates of D. hansenii representing six different phenotypes were collected from seven Danish producers of surface ripened cheeses. ITS-PCR was evaluated for differentiation at species level on the 40 strains obtained from culture collections. Ten strains of each variety of D. hansenii and five strains of each of the above mentioned species were analysed. For each of the investigated species, a specific ITS1-5.8S rDNA-ITS2 region size was observed. Accordingly ITS-PCR was found valuable for differentiation at species level of yeasts of importance for surface ripened cheeses. ITS-PCR RFLP was investigated for the purpose of strain typing of D. hansenii. Ten CBS strains of each variety of D. hansenii were analysed. Only one enzyme (TaqI) out of several investigated (BamHI, DpnI, Fnu4HI, HaeIII, HindIII, HpaII, NlaII, Sau3AI, TaqI) demonstrated genetic diversity within the strains. This enzyme divided the 20 strains in three groups. Sequence analysis of the ITS1-5.8S rDNA-ITS2 region for the type strains of each variety of D. hansenii showed an identity of 99.84%, corresponding to a difference in one basepair. Based on these results, ITS-PCR RFLP was found ineffective for strain typing of D. hansenii. MtDNA RFLP using HaeIII and HpaII was evaluated for strain typing of D. hansenii on the 20 CBS strains of D. hansenii. The CBS strains were divided into 16 groups according to their restriction profiles, which proved the method useful for typing of D. hansenii at subspecies level. The 20 dairy isolates showed a lower genetic variability than the CBS strains as they were divided into eight groups. Cluster analysis of the 20 CBS strains and the 20 dairy isolates based on their mtDNA restriction profiles showed (max. similarity level = 52%) that the dairy isolates only clustered with the CBS strains of D. hansenii var. hansenii. For some of the dairies more than one strain of D. hansenii were found to be involved in the ripening process, indicating that the method could be useful for subspecies typing and investigation of the microbial succession between strains of D. hansenii during the ripening process of surface ripened cheeses.

[The effect of dietary oils on blood lipids and the risk of ischemic heart disease with special emphasis on olive oil. A literature review]

INTRODUCTION

The European Union is financing a large-scale campaign, in which olive oil is represented as the optimal fat for dietetic prevention of coronary heart disease.

METHOD

We reviewed all controlled dietary studies comparing the effect on blood lipids of olive oil and alternative vegetable oils. Fifteen studies were identified.

RESULTS

Consumption of olive oil was associated with significantly raised plasma concentrations of low density lipoprotein cholesterol (+6.5%), high density lipoprotein cholesterol (), and triglycerides (+7%) as compared with an average of the alternative oils. In the light of these differences in blood lipids and the risk coefficients published earlier, we calculated that the consumption of olive oil was associated with a 7% increase in the risk of coronary heart disease.

CONCLUSION

We conclude that olive oil cannot be considered more cardioprotective than other unsaturated vegetable oils as judged from its effects on blood lipids.

Phenotypic and genetic diversity of Saccharomyces contaminants isolated from lager breweries and their phylogenetic relationship with brewing yeasts

A taxonomic study was carried out for isolates of Saccharomyces spp. identified as contaminants ("wild yeast") in 24 different lager breweries. With reference to the current taxonomy all isolates were found to belong to the Saccharomyces sensu stricto complex and 58% of the isolates were further identified as S. cerevisiae, 26% as S. pastorianus and 3% as S. bayanus. The remaining isolates (13%) could not be identified to the species level based on their phenotypic characteristics. However, some of these isolates were identified as S. cerevisiae by HaeIII restriction digest of PCR-amplified intergenic transcribed spacer (ITS) regions. Chromosome length polymorphism (CLP) was evident among the Saccharomyces brewing contaminants with chromosome profiles typical of Saccharomyces sensu stricto. Based upon cluster analysis of their chromosome profiles the majority of the brewing contaminants could be grouped as either S. cerevisiae or S. pastorianus/S. bayanus. Further, the technique was able to differentiate between almost all brewing contaminants and to separate them from any specific lager brewing yeast. The diversity of the Saccharomyces brewing contaminants clearly demonstrated by their CLP was further reflected by MAL genotyping. For the majority of the isolates more than two MAL loci were found with MAL1, MAL2 MAL3, MAL4 and MAL11, MAL31, MAL41 as the dominant genotypes. For all isolates MAL11 and MAL31 were found whereas MAL61 only was found for one isolate. The high number of MAL loci found in the SaccharomYces brewing contaminants indicate their adaptation to a maltose-enriched environment.

Individual cells of Saccharomyces cerevisiae and Zygosaccharomyces bailii exhibit different short-term intracellular pH responses to acetic acid

The effects of perfusion with 2.7 and 26 mM undissociated acetic acid in the absence or presence of glucose on short-term intracellular pH (pH(i)) changes in individual Saccharormyces cerevisiae and Zygosaccharomyces bailii cells were studied using fluorescence-ratio-imaging microscopy and a perfusion system. In the S. cerevisiae cells, perfusion with acetic acid induced strong short-term pH(i) responses, which were dependent on the undissociated acetic acid concentration and the presence of glucose in the perfusion solutions. In the Z. bailii cells, perfusion with acetic acid induced only very weak short-term pH(i) responses, which were neither dependent on the undissociated acetic acid concentration nor on the presence of glucose in the perfusion solutions. These results clearly show that Z. bailii is more resistant than S. cerevisiae to short-term pH(i) changes caused by acetic acid.

Characterization of Saccharomyces cerevisiae strains from spontaneously fermented maize dough by profiles of assimilation, chromosome polymorphism, PCR and MAL genotyping

Several isolates of Saccharomyces cerevisiae from indigenous spontaneously fermented maize dough have been characterized with the purpose of selecting appropriate starter cultures and methods for their subspecies typing. The techniques applied included assimilation of carbon compounds by the API ID 32 C kit, determination of chromosome profiles by PFGE, PCR and MAL genotyping. For the 48 isolates investigated, use of the API ID 32 C kit resulted in eight different assimilation profiles. The most common assimilation profile was the ability of 50% of the isolates to assimilate galactose, saccharose, DL-lactate, raffinose, maltose and glucose. Both chromosome and PCR profiles could be used for subspecies typing of the isolates and on this basis, the isolates were grouped into clusters. The discriminative power of the two techniques was equal; a few isolates not separated by their chromosome profiles could be separated by their PCR profiles and vice versa. Four different MAL genotypes were observed with MAL11 and MAL31 predominating. MAL11 was seen for all isolates whereas no evidence of MAL21 and MAL41 was observed. Based on the results obtained, a high number of Saccharomyces cerevisiae isolates were found to be involved throughout the spontaneous fermentation of maize dough. All methods included appeared to be suitable for subspecies typing. However, the discriminative power was highest for the PFGE and PCR techniques.

Multiple alpha-glucoside transporter genes in brewer's yeast

Maltose and maltotriose are the two most abundant fermentable sugars in brewer's wort, and the rate of uptake of these sugars by brewer's yeast can have a major impact on fermentation performance. In spite of this, no information is currently available on the genetics of maltose and maltotriose uptake in brewing strains of yeast. In this work, we studied 30 brewing strains of yeast (5 ale strains and 25 lager strains) with the aim of examining the alleles of maltose and maltotriose transporter genes contained by them. To do this, we hybridized gene probes to chromosome blots. Studies performed with laboratory strains have shown that maltose utilization is conferred by any one of five unlinked but highly homologous MAL loci (MAL1 to MAL4 and MAL6). Gene 1 at each locus encodes a maltose transporter. All of the strains of brewer's yeast examined except two were found to contain MAL11 and MAL31 sequences, and only one of these strains lacked MAL41. MAL21 was not present in the five ale strains and 12 of the lager strains. MAL61 was not found in any of the yeast strains. In three of the lager strains, there was evidence that MAL transporter gene sequences occurred on chromosomes other than those known to carry MAL loci. Sequences corresponding to the AGT1 gene, which encodes a transporter of several alpha-glucosides, including maltose and maltotriose, were detected in all but one of the yeast strains. Homologues of AGT1 were identified in three of the lager strains, and two of these homologues were mapped, one to chromosome II and the other to chromosome XI. AGT1 appears to be a member of a family of closely related genes, which may have arisen in brewer's yeast in response to selective pressure.

Detection and identification of wild yeasts in lager breweries

Wild yeasts were detected in 41 out of 101 brewery yeast samples investigated using six different selective principles. Malt extract, yeast extract, glucose, peptone (MYGP) agar supplemented with 195 ppm CuSO4 was found to be the most effective selective principle, detecting wild yeasts in 80% of the contaminated samples. Both Saccharomyces and non-Saccharomyces wild yeasts were detected on this medium. Lysine medium, crystal violet medium and incubation of non-selective media at 37 degrees C detected wild yeasts in 46-56% of the contaminated samples. On using actidione medium, only 20% of the wild yeasts were detected. The combined use of MYGP supplemented with 195 ppm CuSO4 and one of the other selective principles did not improve the recovery of the wild yeasts. The wild yeasts found consisted of Saccharomyces cerevisiae (57%), Pichia spp. (28%) and Candida spp. (15%). Using the API ID 32 C kit, 35 different assimilation profiles were obtained for the 124 wild yeast isolates investigated. All isolates were capable of glucose assimilation, whereas only 79% of the isolates assimilated saccharose, 75% maltose, 70% galactose, 65% raffinose and 65% lactate. Lactose, inositol, rhamnose and glucuronate were not assimilated by any of the isolates. The differences in assimilation pattern did not reflect any differences in recovery by the selective principles investigated. The majority of the wild yeast isolates investigated were capable of growth in wort and beer, indicating their possible role as spoilage organisms. The Sacch. cerevisiae isolates were found to be the most hazardous, with some isolates being capable of extensive growth in bottled beer within seventeen days at ambient temperature.

Specific spoilage organisms in breweries and laboratory media for their detection

The Gram positive bacteria are generally regarded as the most hazardous beer spoilage organisms in modern breweries, especially the lactobacilli: L. brevis, L. lindneri, L. curvatus, L. casei, L. buchneri, L. coryneformis, L. plantarum, L. brevisimilis, L. malefermentans and L. parabuchneri and the pediococci: P damnosus, P. inopinatus and P. dextrinicus. Micrococcus kristinae is the only species within the micrococci relevant to brewing. The Gram negative strictly anaerobic bacteria are apparently increasing in importance and include Pectinatus cerevisiiphilus, Pectinatus frisingensis and Selenomonas lacticifex, reported as obligate beer spoilage organisms: Zymophilus raffinosivorans as a potential beer spoilage organism; Megasphaera cerevisiae as an obligate spoilage organism of low alcohol beer and Zymomonas mobilis as capable of spoiling primed beer. With improved process technology the importance of aerobic bacteria has decreased and the same applies for the Gram negative aerobic bacteria Hafnia protea and Enterobacter cloacae which are capable of surviving beer fermentation. Beer spoilage organisms include several so-called wild yeasts, of which Saccharomyces species are generally considered the most important. Even though the detection of beer spoilage organisms by cultivation in laboratory media does not always provide the specificity and the sensitivity required, the use of selective media and incubation conditions still appears to be the method preferred by breweries. The media used depend on the type of sample, the specificity required and, for detection of wild yeasts, to some extent, the characteristics of the culture yeast. Among the media reported so far no single medium can be used to detect all members within a group of specific beer spoilage organisms and further work on the development of improved substrates are required both for bacteria and wild yeasts.

Enhancement of hammerhead ribozyme catalysis by glyceraldehyde-3-phosphate dehydrogenase

A specific tumour necrosis factor alpha ribozyme (TNF-alpha-Rz) binding activity has been purified and identified by N-terminal microsequencing as the glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase (GAPDH). The purified protein as well as commercial GAPDH binds tightly to TNF-alpha ribozyme compared to a variety of other ribozymes and RNAs. Binding of GAPDH to the TNF-alpha-Rz and its derivatives was inhibited by NAD+ and ATP, suggesting that the GAPDH Rossmann fold structure is a part of the ribozyme binding site. Interestingly, GAPDH increased the in vitro cleavage rates of hammerhead ribozymes by up to 25-fold, while no significant stimulation was observed with the lactate dehydrogenase (LDH). This effect was found to be due to the unfolding activity of GAPDH. In fact, pulse-chase experiments demonstrate directly that GAPDH has the capacity to accelerate the ribozyme/substrate association, especially of ribozymes and/or substrates whose predicted secondary structure might interfere with the association step. Under our conditions, the presumed unfolding activity of GAPDH also enhances the turnover of ribozymes by increasing the rate of product dissociation, although only for short cleavage products. Longer duplexes required more incubation time to dissociate. In vitro non-specific interaction of the GAPDH with hammerhead ribozymes and RNA substrates was found to be adequate for the cleavage enhancement effect to occur. However, an analysis of the ability of various prototypical ribozymes to inhibit the expression of interleukin-2 suggests that the addition of a sequence having a high affinity for GAPDH improves the efficacy of ribozymes in the cells. Thus the characterization of cellular proteins with unfolding activity, which specifically bind to hammerhead ribozyme, should facilitate the design of a more effective ribozyme in vivo.

Characterization of naturally occurring autoantibodies against tumour necrosis factor-alpha (TNF-alpha): in vitro function and precise epitope mapping by phage epitope library

Naturally occurring autoantibodies against cytokines exist in the sera of patients with autoimmune diseases as well as in the sera of normal individuals. We report here that affinity-purified autoantibodies against human TNF-alpha from one rheumatoid arthritis (RA) patient inhibited the cytotoxic effect of TNF-alpha on the mouse fibrosarcoma cell line WEHI 164, by 50%. In an attempt to predict the autoantibodies' recognition site on TNF-alpha protein we screened a random nanopeptide phage library with the affinity-purified TNF-alpha autoantibodies. Among 63 random selected clones, 46 clones carried the sequence ASSLLASSP, NSSPYLNTK or PQSPGSSFP. Frequency analysis of the relative occurrence of the 20 amino acids in the nanopeptides displayed by 50 random bacteriophages picked before selection and 63 after selection to bind to TNF-alpha autoantibodies indicated that proline (P < 0.0003) and serine (P < 0.04) are involved in the binding of the autoantibodies to the phages. Furthermore, we demonstrated that three synthetic peptides (ASSLLASSP, NSSPYLNTK and PPLKPVIDE) displayed by the selected phages reduced the binding of the autoantibodies to TNF-alpha protein by 50%. Interestingly, the sera of mice (BALB/c) immunized with phages displaying ASSLLASSP and NSSPYLNTK peptide showed an anti-TNF-alpha response as detected by ELISA. This response was not found in mice immunized with the wild type phage. Thus, the recombinant phages selected from the phage libraries could be used as carrier for immunization, and therefore as a tool for vaccine development. This work sets the stage for experiments designed to isolate ligands for protective antibodies.

Significance of yeasts and moulds occurring in maize dough fermentation for 'kenkey' production

Yeasts and moulds associated with the fermentation of maize dough during the processing of the West African traditional food 'kenkey' were investigated. A mixed flora comprising Candida, Saccharomyces, Trichosporon, Kluyveromyces and Debaryomyces species were isolated from raw maize, during steeping and early phases of fermentation. After 24-48 h of fermentation, Candida krusei and Saccharomyces cerevisiae dominated reaching counts exceeding 10(6) cfu/g. This succession of yeast populations and the significant multiplication of C. krusei and S. cerevisiae were observed in all cases for both the fermentation and the production sites investigated. Penicillium, Aspergillus and Fusarium species, including potential mycotoxin producers, were isolated from raw maize. Initial high counts of 10(5) cfu/g for moulds were reduced to less than 10(2)cfu/g within 24 h of fermentation. High levels of aflatoxins were observed in raw maize, and they were not affected during the fermentations.

Flow cytometric detection of wild yeast in lager breweries

A flow cytometric method for detection of wild yeast infections in breweries is reported. It is based on selective enrichment in Malt extract Yeast extract Glucose Peptone broth (MYGP) at 37 degrees C and in MYGP with 200 ppm CuSO4 at 25 degrees C, staining with a fluorochrome precursor and flow cytometry. In experiments with several types of wild yeast isolated from breweries and two different strains of lager yeast it has been possible to detect one wild yeast per 10(6) culture yeast after 48-72 h of incubation and, in some cases, after 24 h.

Determination of cardiac output with a modified Fick method using estimated instead of measured oxygen consumption

Cardiac output (CO) was determined with a modification of the Fick method using estimated, instead of measured, oxygen consumption values. This avoids several possible sources of error in connection with air sampling and oxygen content analysis, thus a relaxed, steady state is obtained more easily. Using the thermodilution technique a good correlation with CO values was found (r = 0.92, p less than 0.001). We conclude that the modified Fick method is simple, accurate and offers reproducible CO estimates in the majority of patients.

Reduced tubular reabsorption of phosphate during post-operative glucose infusions in humans

It is well-known that serum phosphate concentration decreases considerably during post-operative glucose infusions. The purpose of this study was to elucidate whether the renal handling of phosphate could be responsible for this fall. Twelve patients were studied during glucose and saline infusions on the 2 first post-operative days. The maximal tubular capacity for reabsorption of phosphate per litre of glomerulus filtrate (TmP/GFR) was significantly reduced during glucose infusions in relation to saline infusions. The glucose induced fall in serum phosphate concentration was correlated to the change in TmP/GFR (r2 = 0.71). This study did not explain the reduced TmP/GFR during the glucose infusions, but a high correlation was found between TmP/GFR and the changes in plasma glucose concentration during the infusions (r = -0.91).