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Biomedical subjects

P A de Groot

Publications and source records attributed to P A de Groot.

8 recordsLinked to original sources
PubMed2026

Moderate expression and activity of flocculins underlie the characteristic flocculation phenotype of Saccharomyces pastorianus.

Flocculation is a key technological trait in lager brewing, governing fermentation performance, yeast recovery, and beer quality. In the allo-aneuploid hybrid yeast Saccharomyces pastorianus, the genetic basis of flocculation remains poorly resolved due to its complex dual sub-genome architecture. Here, we systematically re-annotated and functionally characterized the complete FLO gene repertoire of the Group II strain CBS 1483. Thirteen FLO genes were identified, including allelic variants and a previously uncharacterized adhesin, Flo12, containing a Hyphal_reg_CWP domain instead of the canonical PA14 lectin-binding domain. Structural modeling revealed strong conservation of Ca²+-binding residues in PA14 domains, alongside repeat-region diversification likely contributing to functional variability. Using optogenetic expression in a FLO-null background, we demonstrated that SpcI-FLO9-1 and SpcI-FLO9-2_1 are the strongest drivers of flocculation, exhibiting NewFlo-like sugar sensitivity. Transcriptomic analysis during 17°P wort fermentation showed dynamic induction of these genes coinciding with flocculation onset. Surprisingly, deletion of both loci in CBS 1483 did not abolish but only delayed sedimentation in wort, accompanied by improved maltose utilization and attenuation. These findings reveal functional redundancy and compensatory mechanisms within the FLO network of lager yeast, highlighting the genetic complexity underlying flocculation, and providing a molecular framework to inform yeast selection, strain development, and optimization of the lager fermentation processes.IMPORTANCEFlocculation, the process by which yeast cells aggregate and settle, is essential for producing clear, high-quality lager beer, and for efficient yeast recovery during brewing. However, the genetic basis of this trait in lager yeast has remained poorly understood because these strains possess unusually complex hybrid genomes. In this study, we systematically identified and characterized the complete set of flocculation genes in the industrial lager yeast Saccharomyces pastorianus CBS 1483. We demonstrated that lager yeast flocculation is not controlled by a single dominant gene, but instead emerges from the combined action of several moderately active adhesion proteins that are expressed at low levels during fermentation. Surprisingly, deleting the two strongest candidate genes only delayed, rather than eliminated, sedimentation, revealing a robust compensatory network that preserves brewing performance. These findings refine the current understanding of yeast flocculation and provide a molecular framework for developing brewing strains with improved fermentation efficiency, product consistency, and flavor quality.

Saccharomyces pastorianus↗
PubMed2001

History effects and phase diagram near the lower critical point in YBa2Cu3O7 single crystals.

Using a sensitive torque magnetometer we have studied magnetization curves for untwinned overdoped YBa2Cu3O7 single crystals in fields of up to 28 T. We demonstrate the existence of history effects below the lower critical point and provide a full demarcation of the Bragg-glass phase. A pronounced symmetry is observed in the behavior of the phase lines, irreversible magnetization, and value of the magnetization jump near both critical points.

Journal Article↗
PubMed1996

Detection of antibodies to Salmonella enteritidis in sera and yolks from experimentally and naturally infected chickens.

An indirect enzyme-linked immunosorbent assay (ELISA) based on the lipopolysaccharide (LPS) of Salmonella enteritidis phage type 4, was developed for the detection of antibodies to salmonella. Sera and yolks from chickens infected experimentally with S enteritidis showed strong positive reactions. Cross-reactions occurred with sera from chickens inoculated with S typhimurium or S gallinarum. Cross-reactions were weak with sera from chickens infected with five strains of other Enterobacteriaceae. The ELISA was tested with sera and yolks from commercial poultry flocks which were bacteriologically negative for salmonella or infected with salmonella serotypes belonging to serogroup D or to other serogroups. The serological reactions were strong in most flocks infected with S enteritidis and were weaker in flocks infected with S typhimurium. In some flocks infected with these serotypes no antibodies were detected. The correct setting of the cut-off value of the optical density in the ELISA makes it possible to discriminate between chickens which are infected with S enteritidis and chickens which are not infected with S enteritidis.

Animals↗
PubMed1995

[Consensus depression in adults. Dutch Association for Psychiatry].

Depression is a frequent and treatable disorder, but it is insufficiently recognized. A generally used classification system is lacking. In a consensus meeting the following terms were defined: a normal feeling of depression, depression as a symptom and depression as an illness. The use of the term 'masked depression' was advised against. The undertreatment mentioned is caused by the following factors: presentation of physical symptoms by depressive patients, unfamiliarity of patients with depressive disorders and difficulties of patients and GPs in labelling depression as mental. Depressive disorders have various causes. For scoring the severity of depression the Bech version of the Hamilton Depression Rating Scale is preferred. There is no valid laboratory test for diagnosing depression. Laboratory tests are recommended to exclude physical disorders, for choosing an antidepressant and for the follow-up of drug treatment. Cognitive Behavioural Therapy and Interpersonal Therapy are preferred psychotherapeutic methods because of their scientifically proved efficacy. Women suffer from depression twice as frequently as men, which is due to social factors rather than to genetic or hormonal factors. Therefore hormonal therapy is not indicated, a more equal doctor-patient relationship is. Patients with a depressive disorder may consider suicide; this should regularly be discussed with them.

Adult↗
PubMed1992

Predicting symptoms of depression from reports of early parenting: a one-year prospective study in a community sample.

The purpose of this study was to determine whether (reported) parental over involvement and lack of affection identify initially healthy subjects at risk for depression. One thousand subjects from the province of Utrecht, the Netherlands were randomly selected by using telephone addresses and asked to participate in a one-year prospective study on psychological risk factors of depression. From the 108 subjects that finally participated on both occasions, the reports of parental upbringing (Parental Bonding Instrument) of initially non-depressed subjects with a Zung Self-rating Depression Scale score below 49 points were used to predict new cases of depression one year later. Initially non-depressed subjects who reported maternal over involvement in the upper quartile of the distribution had an 8.5-fold increased risk (95% confidence interval 0.9 to 80.6) of becoming depressed one year later. Although initial reports of low paternal affection were positively associated with initial symptoms of depression, this characteristic failed to show predictive value. Parental upbringing deficiencies have frequently been shown in cross-sectional inpatient studies in which retrospective retrieval from memory because of depressive state characteristics may have caused negative colouring. Our results would suggest that maternal over involvement reported in the absence of a depressed mood still proves to be an important psychological risk factor in the aetiology of depression.

Adult↗
PubMed1986

Brain gangliosides in the presenile dementia of Pick.

Histochemical analysis of frontal and temporal lobes from four patients with Pick presenile dementia indicated intracellular and extracellular deposits of gangliosides. Thin layer chromatography of gangliosides disclosed the presence of an unknown ganglioside, a decrease of N-acetylgalactosamine-GDla and an increase of GTla and/or GD2 in white matter of Pick brain. Chromatography of gray matter and quantitation of the sialic acid content yielded results similar to controls. It is suggested that degradation and removal of gangliosides is incomplete in Pick disease.

Chromatography, Thin Layer↗