Biology subjects

Brandt, N.

Publications and source records attributed to Brandt, N..

10 recordsLinked to original sources

bioRxiv2026

Insights from sourdough redefine the domestication landscape of baker's yeast

While the domestication of plants and animals is widely recognized for its role in the rise of human civilization, humans have also cultivated microbes over millennia to produce food and beverages. One microbe in particular, Saccharomyces cerevisiae, is associated with a wide variety of human-fermentation environments, including wine, beer, and notably bread, such that it is often referred to as "bakers yeast." To better illuminate the domestication history of baking associated yeast, we isolated 38 Saccharomyces cerevisiae strains from sourdough starters donated by bakers throughout North America and compared them to thousands of S. cerevisiae isolates from a variety of wild and human-fermentation environments. We identified 6 major clades with two primary domestication hubs, Mediterranean liquid-state fermentation and Asian solid-state fermentation, diverging across Eurasia that gave rise to human-associated lineages. Population genomic analyses demonstrate that S. cerevisiae strains found in sourdough starters are genetically distinct from commercial baking strains and do not come from the surrounding wild environment. Our results show that sourdough yeast strains are closely related to each other and have shared ancestry with strains isolated from various Asian solid state grain fermentations such Japanese sake, Asian rice wines, Chinese distilled spirits (baijiu), and Chinese steamed bread (mantou). We found evidence of significant admixture throughout S. cerevisiae populations, including baking-associated lineages, likely facilitated by human activity. Pangenome gene content largely captures S. cerevisiae traditional genomic sequence-based population structure and reflects human cultural practices, with differences in gene content and copy number between baking associated strains and other groups. Overall, we show that many generalized hallmarks of domestication, such as genome contraction, loss of genetic diversity, and lack of niche expansion, are not universal features of S. cerevisiae domestication, and that baking-associated yeasts have a complex evolutionary history heavily shaped by human culture.

evolutionary biology↗

bioRxiv2026

Structures and broad-spectrum growth-inhibiting activity of formomarinobactin, formylated marinobactin analogues from the Pseudomonas lutea clade

Pseudomonas graminis LMG 21661T, an environmental strain of the P. lutea clade, produces the siderophore formomarinobactin, a novel marinobactin-like siderophore. Mass spectrometry revealed that formomarinobactin shares the same six-residue peptide backbone as marinobactin but contains formylated rather than acetylated N-hydroxyornithines. Alike marinobactins, formomarinobactins are produced as a suite of siderophores with a conserved hexapeptide core but varying lipid tail lengths (C10-C14), shorter than the C12 to C18 characteristic of marinobactins. Both the biosynthesis and cognate receptor genes of the formomarinobactin system in P. graminis are iron regulated but unaffected by zinc or nickel underscoring their role in iron homeostasis. Genome mining combined with mass analyses demonstrated that formomarinobactin production is a conserved trait across the P. lutea clade, with one exception which appears to represent an intraspecific cheater that has lost siderophore production. Beyond the producing strains themselves, we identified a widespread distribution of putative formomarinobactin receptors among diverse Pseudomonas species, revealing a substantial capacity within the P. fluorescens super clade to pirate formomarinobactin as an iron source. Putative receptors were also found in genera outside the Pseudomonas genus. Growth stimulation assays confirmed functional formomarinobactin uptake in several Pseudomonas spp. and a Phytopseudomonas strain, with genetic validation in Pseudomonas rhodesiae. Importantly, formomarinobactin production confers more than a nutritional advantage. Members of the P. lutea clade producing formomarinobactin display pronounced growth inhibiting activity against a broad spectrum of clinical and environmental Gram-positive and with lower efficacy against Gram-negative bacteria. Purified formomarinobactin was able to inhibit growth under iron-limiting conditions and to a lesser extent in iron-rich conditions, highlighting a dual role for this molecule in both iron acquisition and microbial growth inhibition.

microbiology↗

bioRxiv2024

Temperature affects recombination rate plasticity and meiotic success between thermotolerant and cold tolerant yeast species

Meiosis is required for the formation of gametes in all sexually reproducing species and the process is well conserved across the tree of life. However, meiosis is sensitive to a variety of external factors, which can impact chromosome pairing, recombination, and fertility. For example, the optimal temperature for successful meiosis varies between species of plants and animals. This suggests that meiosis is temperature sensitive, and that natural selection may act on variation in meiotic success as organisms adapt to different environmental conditions. To understand how temperature alters the successful completion of meiosis, we utilized two species of the budding yeast Saccharomyces with different temperature preferences: thermotolerant Saccharomyces cerevisiae and cold tolerant Saccharomyces uvarum. We surveyed three metrics of meiosis: sporulation efficiency, spore viability, and recombination rate in multiple strains of each species. As per our predictions, the proportion of cells that complete meiosis and form spores is temperature sensitive, with thermotolerant S. cerevisiae having a higher temperature threshold for successful meiosis than cold tolerant S. uvarum. We confirmed previous observations that S. cerevisiae recombination rate varies between strains and across genomic regions, and add new results that S. uvarum has higher recombination rates than S. cerevisiae. We find that temperature significantly influences recombination rate plasticity in S. cerevisiae and S. uvarum, in agreement with studies in animals and plants. Overall, these results suggest that meiotic thermal sensitivity is associated with organismal thermal tolerance, and may even result in temporal reproductive isolation as populations diverge in thermal profiles.

genetics↗

bioRxiv2024

DNA replication errors are a major source of adaptive gene amplification

Copy number variants (CNVs)--gains and losses of genomic sequences--are an important source of genetic variation underlying rapid adaptation and genome evolution. However, despite their central role in evolution little is known about the factors that contribute to the structure, size, formation rate, and fitness effects of adaptive CNVs. Local genomic sequences are likely to be an important determinant of these properties. Whereas it is known that point mutation rates vary with genomic location and local DNA sequence features, the role of genome architecture in the formation, selection, and the resulting evolutionary dynamics of CNVs is poorly understood. Previously, we have found that the GAP1 gene in Saccharomyces cerevisiae undergoes frequent and repeated amplification and selection under long-term experimental evolution in glutamine-limiting conditions. The GAP1 gene has a unique genomic architecture consisting of two flanking long terminal repeats (LTRs) and a proximate origin of DNA replication (autonomously replicating sequence, ARS), which are likely to promote rapid GAP1 CNV formation. To test the role of these genomic elements on CNV-mediated adaptive evolution, we performed experimental evolution in glutamine-limited chemostats using engineered strains lacking either the adjacent LTRs, ARS, or all elements. Using a CNV reporter system and neural network simulation-based inference (nnSBI) we quantified the formation rate and fitness effect of CNVs for each strain. We find that although GAP1 CNVs repeatedly form and sweep to high frequency in strains with modified genome architecture, removal of local DNA elements significantly impacts the rate and fitness effect of CNVs and the rate of adaptation. We performed genome sequence analysis to define the molecular mechanisms of CNV formation for 177 CNV lineages. We find that across all four strain backgrounds, between 26% and 80% of all GAP1 CNVs are mediated by Origin Dependent Inverted Repeat Amplification (ODIRA) which results from template switching between the leading and lagging strand during DNA synthesis. In the absence of the local ARS, a distal ARS can mediate CNV formation via ODIRA. In the absence of local LTRs, homologous recombination mechanisms still mediate gene amplification following de novo insertion of retrotransposon elements at the locus. Our study demonstrates the remarkable plasticity of the genome and reveals that template switching during DNA replication is a frequent source of adaptive CNVs.

evolutionary biology↗

bioRxiv2024

A comparison of lipid diffusive dynamics in monolayers and bilayers in the context of interleaflet coupling

Cellular membranes are composed of lipids typically organized in a double-leaflet structure. Interactions between these two leaflets - often referred to as interleaflet coupling - play a crucial role in various cellular processes. Despite extensive study, the mechanisms governing such interactions remain incompletely understood. Here, we investigate the effects of interleaflet coupling from a specific point of view, i.e. by comparing diffusive dynamics in bilayers and monolayers, focusing on potential lipid-specific interactions between opposing leaflets. Through quantitative fluorescence microscopy techniques, we characterize lipid diffusion and mean molecular area in monolayers and bilayers composed of different lipids. Our results suggest that the observed decrease in bilayer lipid diffusion compared to monolayers depends on lipid identity. Furthermore, our analysis suggests that lipid acyl chain structure and spatial configuration at the bilayer may strongly influence interleaflet interactions and dynamics in bilayers. These findings provide insights into the role of lipid structure in mediating interleaflet coupling and underscore the need for further experimental investigations to elucidate the underlying mechanisms.

biophysics↗

bioRxiv2024

The recombination landscape of introgression in yeast

Meiotic recombination is an evolutionary force that acts by breaking up genomic linkage, increasing the efficacy of selection. Recombination is initiated with a double-strand break which is resolved via a crossover, which involves the reciprocal exchange of genetic material between homologous chromosomes, or a non-crossover, which results in small tracts of non-reciprocal exchange of genetic material. Crossover and non-crossover rates vary between species, populations, individuals, and across the genome. In recent years, recombination rate has been associated with the distribution of ancestry derived from past interspecific hybridization (introgression) in a variety of species. We explore this interaction of recombination and introgression by sequencing spores and detecting crossovers and non-crossovers from two crosses of the yeast Saccharomyces uvarum. One cross is between strains which each contain introgression from their sister species, S. eubayanus, while the other cross has no introgression present. We find that the recombination landscape is significantly different between S. uvarum crosses, and that some of these differences can be explained by the presence of introgression in one cross. Crossovers are reduced and non-crossovers are increased in heterozygous introgression compared to syntenic regions in the cross without introgression. This translates to reduced allele shuffling within introgressed regions, and an overall reduction of shuffling on most chromosomes with introgression compared to the syntenic regions and chromosomes without introgression. Our results suggest that hybridization can significantly influence the recombination landscape, and that the reduction in allele shuffling contributes to the initial purging of introgression in the generations following a hybridization event.

evolutionary biology↗

bioRxiv2019

Regulatory kinase genetic interaction profiles differ between environmental conditions and cellular states

Cell growth and quiescence in eukaryotic cells is controlled by an evolutionarily conserved network of signaling pathways. Signal transduction networks operate to modulate a wide range of cellular processes and physiological properties when cells exit proliferative growth and initiate a quiescent state. How signaling networks function to respond to diverse signals that result in cell cycle exit and establishment of a quiescent state is poorly understood. Here, we studied the function of signaling pathways in quiescent cells using global genetic interaction mapping in the model eukaryotic cell, Saccharomyces cerevisiae (budding yeast). We performed pooled analysis of genotypes using molecular barcode sequencing to test the role of [~]3,900 gene deletion mutants and [~]11,700 pairwise interactions between all non-essential genes and the protein kinases TOR1, RIM15, PHO85 in three different nutrient-restricted conditions in both proliferative and quiescent cells. We detect nearly five-fold more genetic interactions in quiescent cells compared to proliferative cells. We find that both individual gene effects and genetic interaction profiles vary depending on the specific pro-quiescence signal. The master regulator of quiescence, RIM15 shows distinct genetic interaction profiles in response to different starvation signals. However, vacuole-related functions show consistent genetic interactions with RIM15 in response to different starvation signals suggesting that RIM15 integrates diverse signals to maintain protein homeostasis in quiescent cells. Our study expands genome-wide genetic interaction profiling to additional conditions, and phenotypes, highlighting the conditional dependence of epistasis.

genetics↗

bioRxiv2018

Single-cell copy number variant detection reveals the dynamics and diversity of adaptation

Copy number variants (CNVs) are a pervasive, but understudied source of genetic variation and evolutionary potential. Long-term evolution experiments in chemostats provide an ideal system for studying the molecular processes underlying CNV formation and the temporal dynamics of de novo CNVs. Here, we developed a fluorescent reporter to monitor gene amplifications and deletions at a specific locus with single-cell resolution. Using a CNV reporter in nitrogen-limited chemostats, we find that GAP1 CNVs are repeatedly generated and selected during the early stages of adaptive evolution resulting in predictable dynamics of CNV selection. However, subsequent diversification of populations defines a second phase of evolutionary dynamics that cannot be predicted. Using whole genome sequencing, we identified a variety of GAP1 CNVs that vary in size and copy number. Despite GAP1s proximity to tandem repeats that facilitate intrachromosomal recombination, we find that non-allelic homologous recombination (NAHR) between flanking tandem repeats occurs infrequently. Rather, breakpoint characterization revealed that for at least 50% of GAP1 CNVs, origin-dependent inverted-repeat amplification (ODIRA), a DNA replication mediated process, is the likely mechanism. We also find evidence that ODIRA generates DUR3 CNVs, indicating that it may be a common mechanism of gene amplification. We combined the CNV reporter with barcode lineage tracking and found that 103-104 independent CNV-containing lineages initially compete within populations, which results in extreme clonal interference. Our study introduces a novel means of studying CNVs in heterogeneous cell populations and provides insight into the underlying dynamics of CNVs in evolution.

evolutionary biology↗

bioRxiv2018

Global analysis of gene expression dynamics identifies factors required for accelerated mRNA degradation

Cellular responses to changing environments frequently involve rapid reprogramming of the transcriptome. Regulated changes in mRNA degradation rates can accelerate reprogramming by clearing or stabilizing extant transcripts. Here, we measured mRNA stability using 4-thiouracil labeling in the budding yeast Saccharomyces cerevisiae during a nitrogen upshift and found that 78 mRNAs are subject to destabilization. These transcripts include Nitrogen Catabolite Repression (NCR) and carbon metabolism mRNAs, suggesting that mRNA destabilization is a mechanism for targeted reprogramming. To explore the molecular basis of destabilization we implemented a SortSeq approach to screen using the pooled deletion collection library for trans factors that mediate rapid GAP1 mRNA repression. We combined low-input multiplexed Barcode sequencing with branched-DNA single-molecule mRNA FISH and Fluorescence-activated cell sorting (BFF) to identify that the Lsm1-7p/Pat1p complex and general mRNA decay machinery are important for GAP1 mRNA clearance. We also find that the decapping modulator SCD6, translation factor eIF4G2, and the 5 UTR of GAP1 are important for this repression, suggesting that translational control may impact the post-transcriptional fate of mRNAs in response to environmental changes.

genetics↗

bioRxiv2017

Adaptive Evolution Of Transcription Factor Binding Affinities

Understanding the molecular basis of gene expression evolution is a central problem in evolutionary biology. However, connecting changes in gene expression to increased fitness, and identifying the functional basis of those changes, remains challenging. To study adaptive evolution of gene expression in real time, we performed long term experimental evolution (LTEE) of Saccharomyces cerevisiae (budding yeast) in ammonium-limited chemostats. Following several hundred generations of continuous selection we found significant divergence of nitrogen-responsive gene expression in lineages with increased fitness. In multiple independent lineages we found repeated selection for non-synonymous mutations in the zinc finger DNA binding domain of the activating transcription factor (TF), GAT1, that operates within incoherent feedforward loops to control expression of the nitrogen catabolite repression (NCR) regulon. Missense mutations in the DNA binding domain of GAT1 reduce its binding affinity for the GATAA consensus sequence in a promoter-specific manner, resulting in increased expression of ammonium permease genes via both direct and indirect effects, thereby conferring increased fitness. We find that altered transcriptional output of the NCR regulon results in antagonistic pleiotropy in alternate environments and that the DNA binding domain of GAT1 is subject to purifying selection in natural populations. Our study shows that adaptive evolution of gene expression can entail tuning expression output by quantitative changes in TF binding affinities while maintaining the overall topology of a gene regulatory network.

evolutionary biology↗