Biology subjects

Nickerson, K. W.

Publications and source records attributed to Nickerson, K. W..

4 recordsLinked to original sources

bioRxiv2023

Transcriptional regulation of the synthesis and secretion of farnesol and aromatic fusel alcohols in the fungus Candida albicans: Examination of the Homann transcription regulator knockout collection

Candida albicans is an efficient colonizer of human gastrointestinal tracts and skin and is an opportunistic pathogen. C. albicans exhibits morphological plasticity and the ability to switch between yeast and filamentous morphologies is associated with virulence. One regulator of this switch is the quorum sensing molecule farnesol which is produced by C. albicans throughout growth. However, the synthesis, secretion, regulation, and turnover of farnesol is not fully understood. To address this, we used our improved farnesol assay to screen a transcription regulator knockout library of 164 mutants for farnesol accumulation in whole cultures, pellets, and supernatants. All mutants produced farnesol and they averaged 9.2X more farnesol in the pellet than the supernatant. Nineteen mutants had significant differences with ten mutants producing more farnesol than their SN152+ parent while nine produced less. Seven mutants exhibited greater secretion of farnesol while two exhibited less. We examined the time course for farnesol accumulation in six mutants with the greatest accumulation differences and found that those differences persisted throughout growth and they were not time dependent. Significantly, two high accumulating mutants did not exhibit the decay in farnesol levels during stationary phase characteristic of wild type C. albicans, suggesting that a farnesol modification/degradation mechanism is absent in these mutants. Identifying these transcriptional regulators provides new insight into farnesols physiological functions regarding cell cycle progression, white-opaque switching, yeast-mycelial dimorphism, and response to cellular stress.

microbiology↗

bioRxiv2020

A collection of Serratia marcescens differing in their insect pathogenicity towards Manduca sexta larvae

We investigated the ability of Serratia marcescens to kill Manduca sexta (tobacco/tomato hornworm) larvae following injection of ca. 5 x 105 bacteria into the insect hemolymph. Fifteen bacterial strains were examined, including 12 non-pigmented clinical isolates from humans. They fell into 6 groups depending on the timing and rate at which they caused larval death. Relative insect toxicity was not correlated with pigmentation, colony morphology, biotype, motility, capsule formation, iron availability, surfactant production, swarming ability, antibiotic resistance, bacteriophage susceptibility, salt tolerance, nitrogen utilitization patterns, or the production of 4 exoenzymes: proteases, DNase, lipase, or phospholipase. There were marked differences in chitinase production, the types of homoserine lactone (HSL) quorum sensing molecules produced, and the blood agar hemolysis patterns observed. However, none of these differences correlated with the six insect larval virulence groups. Thus, the actual offensive or defensive virulence factors possessed by these strains remain unidentified. The availability of this set of S. marcescens strains, covering the full range from highly virulent to non-virulent, should permit future genomic comparisons to identify the precise mechanisms of larval toxicity.

microbiology↗

bioRxiv2017

Synthesis, secretion, and perception of abscisic acid regulates stress responses in Chlorella sorokiniana

Abscisic acid (ABA) is a phytohormone that has been extensively characterized in higher plants for its roles in seed and bud dormancy, leaf abscission, and stress responses. Genomic studies have identified orthologs for ABA-related genes throughout the Viridiplantae, including in unicellular algae; however, the role of ABA in algal physiology has not been characterized, and the existence of such a role has been a matter of dispute. In this study, we demonstrate that ABA is involved in regulating algal stress responses. Chlorella sorokiniana strain UTEX 1230 contains genes orthologous to those of higher plants which are essential for ABA biosynthesis, sensing, and degradation. RNAseq-based transcriptomic studies reveal that treatment with ABA induces dramatic changes in gene expression profiles, including the induction of a subset of genes involved in DNA replication and repair, a phenomenon which has been demonstrated in higher plants. Pretreatment of C. sorokiniana cultures with ABA exerts a protective effect on cell viability in response to ultraviolet radiation. Additionally, C. sorokiniana produces and secretes biologically relevant amounts of both ABA and the oxylipin 12-oxo-phytodienoic acid (OPDA) into the growth medium in response to abiotic stressors. Taken together, these phenomena suggest that ABA signaling evolved as an intercellular stress response signaling molecule in eukaryotic microalgae prior to the evolution of multicellularity and colonization of land.

plant biology↗

bioRxiv2017

Molecular machinery of auxin synthesis, secretion, and perception in the unicellular chlorophyte alga Chlorella sorokiniana UTEX 1230

Indole-3-acetic acid is a ubiquitous small molecule found in all domains of life. It is the predominant and most active auxin in seed plants, where it coordinates a variety of complex growth and development processes. The potential origin of auxin signaling in algae remains a matter of some controversy. In order to clarify the evolutionary context of algal auxin signaling, we undertook a genomic survey to assess whether auxin acts as a signaling molecule in the emerging model chlorophyte Chlorella sorokiniana UTEX 1230. C. sorokiniana produces the auxin indole-3-acetic acid (IAA), which was present in both the cell pellet and in the supernatant at a concentration of ~ 1 nM, and its genome encodes orthologs of genes related to auxin synthesis, transport, and signaling in higher plants. Candidate orthologs for the canonical AUX/IAA signaling pathway were not found; however, auxin-binding protein 1 (ABP1), an alternate auxin receptor, is present and highly conserved at essential auxin binding and zinc coordinating residues. Additionally, candidate orthologs for PIN proteins, responsible for intercellular, vectorial auxin transport in higher plants, were not found, but PILs (PIN-Like) proteins, a recently discovered family that mediates intracellular auxin transport, were identified. The distribution of auxin related gene in this unicellular chlorophyte demonstrates that a core suite of auxin signaling components was present early in the evolution of plants. Understanding the simplified auxin signaling pathways in chlorophytes will aid in understanding phytohormone signaling and crosstalk in seed plants, and in understanding the diversification and integration of developmental signals during the evolution of multicellular plants.

plant biology↗