The Phaff school of yeast ecology

Herman Jan Phaff’s legacy includes pioneering work on the yeast cell envelope and the application of molecular approaches to yeast systematics. Clearly, his interest and knowledge spanned the whole gamut of yeast biology. Yet, his most original and most heartfelt contribution was to our understanding of the position occupied by yeasts in nature. This view developed through the juxtaposition of his childhood exposure to industrial fermentations and his training in the tradition of Beijerinck’s Delft School of Microbiology. Through some of Phaff’s recent writings, I have attempted to formulate the themes or principles that were implicit to his ecological thinking. Six focal points emerge. (1) Yeasts in themselves are a sufficient object of study. (2) A clear idea of a yeast community cannot be obtained unless the yeast species are correctly identified. (3) Ecologically meaningful conclusions require an adequate sample size. (4) The bacteriological dictum “everything is everywhere” is a poor account of yeast distributions. (5) The habitat is the cornerstone of yeast ecology. (6) Ecology is the most exciting aspect of yeast biology

Gut yeasts do not improve desiccation survival in Drosophila melanogaster

A healthy gut microbiota generally improves the performance of its insect host. Although the effects can be specific to the species composition of the microbial community, the role of gut microbiota in determining water balance has not been well explored. We used axenic and gnotobiotic (reared with a known microbiota) Drosophila melanogaster to test three hypotheses about the effects of gut yeasts on the water balance of adult flies: 1) that gut yeasts would improve desiccation survival in adult flies; 2) that larval yeasts would improve adult desiccation survival; 3) that the effects would be species-specific, such that yeasts closely associated with D. melanogaster in nature are more likely to be beneficial than those rarely found in association with D. melanogaster. We used Saccharomyces cerevisiae (often used in Drosophila cultures, but rarely associated with D. melanogaster in nature), Lachancea kluyveri (associated with some species of Drosophila, but not D. melanogaster), and Pichia kluyveri (associated with D. melanogaster in nature). Adult inoculation with yeasts had no effect on survival of desiccating conditions. Inoculation with P. kluyveri as larvae did not change desiccation survival in adults; however, rearing with L. kluyveri or S. cerevisiae reduced adult desiccation survival. We conclude that adult inoculation with gut yeasts has no impact on desiccation survival, but that rearing with yeasts can have either no or detrimental effect. The effects appear to be species-specific: P. kluyveri did not have a negative impact on desiccation tolerance, suggesting some level of co-adaptation with D. melanogaster. We note that S. cerevisiae may not be an appropriate species for studying the effects of gut yeasts on D. melanogaster

Metschnikowia proteae sp. nov., a nectarivorous insect-associated yeast species from Africa

A collection of yeasts isolated from nectar of flowers of Protea caffra (Proteaceae) and associated scarab beetles (Atrichelaphinis tigrina, Cyrtothyrea marginalis, Trichostetha fascicularis and Heterochelus sp.) and drosophilid flies in South Africa, contained 28 isolates that could not be assigned to known species. Comparisons of the D1/D2 domains of the large subunit rRNA gene demonstrated the existence of three separate phylotypes with an affinity to the genus Metschnikowia and more specifically to the beetle-associated large-spored Metschnikowia clade. Twenty-six strains that had similar D1/D2 sequences were mixed in all pairwise combinations. They were found to mate and give rise to large asci typical of those in the clade. The name Metschnikowia proteae sp. nov. (type strain EBDT1Y1T5CBS 12522T5NRRL Y-48784T; allotype strain EBDC2Y25CBS 125215NRRL Y-48785) is proposed to accommodate this novel species. The ecology of this novel yeast species is discussed in relation to its potential plant and insect host species. The additional two single strains isolated from Heterochelus sp. represent two novel undescribed species (Candida sp. 1 EBDM2Y3 and Candida sp. 2 EBDM8Y1). As these single strains are probably haploid mating types of Metschnikowia species, their description is deferred until the species are sufficiently well sampled to permit meaningful descriptionsPeer reviewe

The role of plant–pollinator interactions in structuring nectar microbial communities

Floral nectar harbours a diverse microbiome of yeasts and bacteria that depend predominantly on animal visitors for their dispersal. Since pollinators visit specific sets of flowers and carry their own unique microbiota, we hypothesize that plant species visited by the same set of pollinators may support non-random nectar microbial communities linked together by the type of pollinator. Here we explore the importance of plant–pollinator interactions in the assembly of nectar microbiome and study the role of plant geographic location as a determinant of microbial community composition. We intensively sampled the nectar of 282 flowers of 48 plant species with beetles, birds, long-tongued and short-tongued insects as pollinators in wild populations in South Africa, one of the world's biodiversity hotspots, and using molecular techniques we identified nectar yeast and bacteria taxa. The analyses provided new insights into the richness, geographic structure and phylogenetic characterization of nectar microbiome, and compared patterns of composition of bacteria and yeast communities in relation to plant and pollinator guild. Our results showed that plant–pollinator interactions played a crucial role in shaping nectar microbial communities. Plants visited by different pollinator guilds supported significantly different yeast and bacterial communities. The pollinator guild also contributed to the maintenance of beta diversity and phylogenetic microbial segregation. The results revealed different patterns for yeast and bacteria; whereas plants visited by beetles supported the highest richness and phylogenetic diversity of yeasts, bacteria communities were significantly more diverse in plants visited by other insect groups. We found no clear microbial spatial segregation at different geographical scales for bacteria, and only the phylogenetic similarity of yeast composition was correlated significantly with geography. Synthesis. Interactions of animal vector, plant host traits and microbe physiology contribute to microbial community assemblages in nectar. Our results suggest that plants visited by the same pollinator guild have a characteristic nectar microbiota signature that may transcends the geographic region they are in. Contrasted patterns for yeast and bacteria stress the need for future work aimed at better understanding the causes and consequences of the importance of plants and pollinators in shaping nectar microbial communities in nature.Ministerio de Economía y Competitividad SEV-2012- 0262Ministerio de Ciencia e Innovación RYC2018-023847-

Reducing cannabis use in young adults with psychosis using iCanChange, a mobile health app : protocol for a pilot randomized controlled trial (ReCAP-iCC)

Background: Cannabis use is the most prevalent among adolescents and young adults; frequent consumption is associated with cannabis use disorder (CUD) and psychosis, with a high prevalence (up to 50%) of CUD in individuals with first-episode psychosis (FEP). Early Intervention Services (EIS) for psychosis include face-to-face psychosocial interventions for CUD, because reducing or discontinuing cannabis use improves clinical and health care service use outcomes. However, multiple barriers (eg, staff availability and limited access to treatment) can hinder the implementation of these interventions. Mobile health (mHealth) interventions may help circumvent some of these barriers; however, to date, no study has evaluated the effects of mHealth psychological interventions for CUD in individuals with FEP. Objective: This study describes the protocol for a pilot randomized controlled trial using a novel mHealth psychological intervention (iCanChange [iCC]) to address CUD in young adults with FEP. iCC was developed based on clinical evidence showing that in individuals without psychosis, integrating the principles of cognitive behavioral therapy, motivational interviewing, and behavioral self-management approaches are effective in improving cannabis use–related outcomes. Methods: Consenting individuals (n=100) meeting the inclusion criteria (eg, aged 18-35 years with FEP and CUD) will be randomly allocated in a 1:1 ratio to the intervention (iCC+modified EIS) or control (EIS) group. The iCC is fully automatized and contains 21 modules that are completed over a 12-week period and 3 booster modules available during the 3-month follow-up period. Validated self-report measures will be taken via in-person assessments at baseline and at 6, 12 (end point), and 24 weeks (end of trial); iCC use data will be collected directly from the mobile app. Primary outcomes are intervention completion and trial retention rates, and secondary outcomes are cannabis use quantity, participant satisfaction, app use, and trial recruiting parameters. Exploratory outcomes include severity of psychotic symptoms and CUD severity. For primary outcomes, we will use the chi-square test using data collected at week 12. We will consider participation in iCC acceptable if ≥50% of the participants complete at least 11 out of 21 intervention modules and the trial feasible if attrition does not reach 50%. We will use analysis of covariance and mixed-effects models for secondary outcomes and generalized estimating equation multivariable analyses for exploratory outcomes. Results: Recruitment began in July 2022, and data collection is anticipated to be completed in July 2024. The main results are expected to be submitted for publication in 2024. We will engage patient partners and other stakeholders in creating a multifaceted knowledge translation plan to reach a diverse audience. Conclusions: If feasible, this study will provide essential data for a larger-scale efficacy trial of iCC on cannabis use outcomes in individuals with FEP and CUD

Genome-wide analysis identifies 12 loci influencing human reproductive behavior.

The genetic architecture of human reproductive behavior-age at first birth (AFB) and number of children ever born (NEB)-has a strong relationship with fitness, human development, infertility and risk of neuropsychiatric disorders. However, very few genetic loci have been identified, and the underlying mechanisms of AFB and NEB are poorly understood. We report a large genome-wide association study of both sexes including 251,151 individuals for AFB and 343,072 individuals for NEB. We identified 12 independent loci that are significantly associated with AFB and/or NEB in a SNP-based genome-wide association study and 4 additional loci associated in a gene-based effort. These loci harbor genes that are likely to have a role, either directly or by affecting non-local gene expression, in human reproduction and infertility, thereby increasing understanding of these complex traits

Phylogenetic analysis of the angiosperm-floricolous insect–yeast association: Have yeast and angiosperm lineages co-diversified?

Metschnikowia (Saccharomycetales, Metschnikowiaceae/Metschnikowia clade) is an ascomycetous yeast genus whose species are associated mostly with angiosperms and their insect pollinators over all continents. The wide distribution of the genus, its association with angiosperm flowers, and the fact that it includes some of the best-studied yeasts in terms of biogeography and ecology make Metschnikowia an excellent group to investigate a possible co-radiation with angiosperm lineages. We performed phylogenetic analyses implementing Bayesian inference and likelihood methods, using a concatenated matrix ( 2.6 Kbp) of nuclear DNA (ACT1, 1st and 2nd codon positions of EF2, Mcm7, and RPB2) sequences. We included 77 species representing approximately 90% of the species in the family. Bayesian and parsimony methods were used to perform ancestral character reconstructions within Metschnikowia in three key morphological characters. Patterns of evolution of yeast habitats and divergence times were explored in the Metschnikowia clade lineages with the purpose of inferring the time of origin of angiosperm-associated habitats within Metschnikowiaceae. This paper presents the first phylogenetic hypothesis to include nearly all known species in the family. The polyphyletic nature of Clavispora was confirmed and Metschnikowia species (and their anamorphs) were shown to form two groups: one that includes mostly floricolous, insect-associated species distributed in mostly tropical areas (the large-spored Metschnikowia clade and relatives) and another that comprises more heterogeneous species in terms of habitat and geographical distribution. Reconstruction of character evolution suggests that sexual characters (ascospore length, number of ascospores, and ascus formation) evolved multiple times within Metschnikowia. Complex and dynamic habitat transitions seem to have punctuated the course of evolution of the Metschnikowiaceae with repeated and independent origins of angiosperm-associated habitats. The origin of the family is placed in the Late Cretaceous (71.7 Ma) with most extant species arising from the Early Eocene. Therefore, the Metschnikowiaceae likely radiated long after the Mid-Cretaceous radiations of angiosperms and their diversification seems to be driven by repeated radiation on a pre-existing diverse resourcePeer reviewe

Nectar yeasts of two southern Spanish plants: the roles of immigration and physiological traits in community assembly

Recent studies have shown that dense yeast populations often occurring in flo- ral nectar are numerically dominated by a few species from the flower–insect interface specialized genus Metschnikowia, while generalist yeast species com- monly occurring on leaf surfaces, soil, freshwater, and air were rarely isolated from nectar samples. This study was designed to understand the main factors responsible for the assembly of nectar yeast communities, by combining field experiments with laboratory tests characterizing the physiological abilities of all yeast species forming the pool of potential colonizers for two Spanish flowering plants (Digitalis obscura and Atropa baetica). Yeast frequency and species rich- ness were assessed in external sources (bee glossae, air, plant phylloplane) as well as in pollinator rewards (pollen, nectar). Yeasts were most frequent in external sources (air, flower-visiting insects), less so in the proximate floral environment (phylloplane), and least in pollen and nectar. Nectar communities appeared to be considerably impoverished versions of those in insect glossae and phylloplane. Nectar, pollen, and insect yeast assemblages differed in physi- ological characteristics from those in other substrates. Nectarivorous Metschnik- owia were not more resistant than other yeast species to plant secondary compounds and high sugar concentrations typical of nectar, but their higher growth rates may be decisive for their dominance in ephemeral nectar commu- nities.Peer reviewe