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At least 19 recordsLinked to original sources
PubMed1992

Photosensitizing activity of water- and lipid-soluble phthalocyanines on prokaryotic and eukaryotic microbial cells.

The photosensitizing activity of lipophilic zinc-phthalocyanine (Zn-Pc) and its water-soluble sulphonated derivative (Zn-PcS) towards Streptococcus faecium and Candida albicans was studied and correlated with the amount of cell-bound photosensitizer. With both micro-organisms Zn-PcS was more tightly bound in larger amounts than Zn-Pc in the protoplasts of the cytoplasmic membrane. As a consequence, the photoinduced damage in S. faecium initially involved membrane proteins, while DNA was modified only upon prolonged irradiation. For C. albicans only Zn-PcS showed a preferential affinity for the spheroplasts and the decrease in cell survival was not accompanied by detectable modifications of the electrophoretic pattern of membrane proteins. The photoinduced ultrastructural alteration of both micro-organisms suggests damage at membrane level. This would indicate the involvement of different targets in bacteria and yeast for phthalocyanine photosensitization.

Candida albicans↗
PubMed2026

Crawling under the radar: Two novel Paulinella species expand knowledge about the ecology and evolution of a primary plastid-containing amoeba lineage.

The genus Paulinella represents a rare, independent case of primary endosymbiosis, providing a unique system to study the early stages of organelle evolution. Here, we expand current understanding of primary plastid endosymbiosis through the discovery and characterization of two novel photosynthetic amoebae, Paulinella marae sp. nov. and Paulinella murrayi sp. nov., isolated from a brackish water habitat in North Carolina, United States. Complete chromatophore genomes and mitochondrial data revealed conserved gene content but notable structural variation, including genome rearrangements and inversion events. Phylogenetic analyses uncovered significant discordance between nuclear and organelle datasets, likely driven by substitution saturation, limited taxon sampling, and differing evolutionary signals across loci. Ecological observations over multiple years indicate that both species are in low abundance but consistently present, and when coupled with hobbyist data, support the hypothesis that photosynthetic Paulinella species are globally distributed yet under-sampled. These results increase known species diversity within the clade from four to six and highlight the importance of integrating field-based observations with genomic approaches. Overall, this work advances Paulinella as a model for studying ongoing primary endosymbiosis, lineage divergence, and the ecological strategies of low-abundance microbial eukaryotes.

Paulinella↗
PubMed1977

Mutation in continuous cultures of Schizosaccharomyces pombe. I. Dependence of the kinetics of mutation accumulation upon the growth-limiting nutrilite.

The rate of spontaneous mutation to resistance to the 12,13-epoxytrichothecene trichodermin has been determined under different growth limiting conditions in continuous cultures of the microbial eukaryote Schizosaccharomyces pombe. In agreement with data obtained in bacterial systems by previous workers the kinetics observed for the accumulation of mutations is found to be dependent upon the nutrient used to limit the growth of the population. Under conditions of glucose-limitation mutation accumulation is directly proportional to the rate of cell division, while under histidine-limitation it is proportional to chronological time. Various possible explanations for these observations are discussed.

Ascomycota↗
PubMed1979

Yeast chromosomal DNA molecules have strands which are cross-linked at their termini.

The microbial eukaryote Saccharomyces cerevisiae has 18 chromosomes, each consisting of a DNA molecule of 1 x 15 x 10(8) daltons (150 to 2,300 kilobase pairs). Interstand cross-links have now been found in molecules of all sizes by examining the ability of high molecular weight DNA to snap back, i.e., to rapidly renature after denaturation. Experiments in which snap back was assessed for molecules broken by shearing indicate that there are probably two cross-links in each chromosome. Evidence that the cross-links occur at specific sites in the genome was obtained by treating total chromosomal DNA with the endonuclease EcoRI which cleaves the yeast genome into approximately 2,000 discrete fragments. Cross-link containing fragments were separated from fragments without cross-links. This purification resulted in enrichment for about 18 specific fragments. To determine whether the cross-links are terminal or at internal sites in chromosomal DNA, large shear-produced fragments were examined by electron microsopy. With complete denaturation few fragments exhibit the X-shaped single strand configuration expected for internal cross-links. When partially denatured fragments were examined some ends had single strand loops as expected for (AT-rich) cross-linked termini. We propose that a duplex chromosomal DNA molecules have cross-linked termini. We propose that a duplex chromosomal DNA molecule in this eukaryote consists of a continuous, single, self-complementary strand of DNA. This structure has implications for the mechanism of chromosome replication and may be the basis of telomere behavior.

Chromosomes↗
PubMed2025

Unisexual reproduction in the global human fungal pathogen Cryptococcus neoformans.

The human fungal pathogen Cryptococcus species complex (encompassing Cryptococcus neoformans, Cryptococcus deneoformans, and the Cryptococcus gattii species complexes) exhibits diversity in sexual reproduction, including α-a mating, pseudosexual reproduction, as well as unisexual reproduction initiated from a single isolate or between isolates of the same mating type. A central conundrum is that while most Cryptococcus natural populations exhibit significant α mating-type bias, genetic and genomic analyses show recombination occurs in nature. The discovery of unisexual reproduction in C. deneoformans provided insight; however, thus far, unisexual reproduction has never been directly observed in the predominant global pathogenic species C. neoformans. Here, we provide evidence that mutating the RIC8 gene, which encodes a conserved guanine nucleotide exchange factor (GEF) involved in both chaperoning and activating Gα proteins, enables unisexual reproduction in C. neoformans. Additionally, we show that genetic variation in the natural population promotes unisexual reproduction, and unisexual reproduction in C. neoformans involves canonical meiotic recombination. Finally, we found that deletion of both GPA2 and GPA3 in the MATα background leads to self-filamentation without sporulation, suggesting that differential modulation of the Gα proteins, likely involving Ric8, could underlie the switch between different modes of sexual reproduction in Cryptococcus. Our study further highlights that the highly conserved Ric8 GEF can act as an important regulator of cellular development in response to environmental stimuli and could modulate sexual reproduction in nature. We hypothesize that unisexual reproduction occurs much more frequently in nature than currently appreciated, and possibly in other fungi and microbial eukaryotes as well.

Cryptococcus neoformans↗
PubMed2026

Biocontrol potential and molecular basis of predation in a marine raptorial ciliate.

Predator-prey interactions are widespread across organisms and are key drivers of morphological and behavioral evolution. Despite this, predation remains poorly understood among microbial eukaryotes, mostly due to the absence of a tractable experimental system that allows quantitative, reproducible investigation. This study establishes the marine raptorial ciliate Chaenea vorax as a highly efficient predator, with Rosenzweig-MacArthur model simulations based on predation data showing that only a few dozen individuals can eliminate the vast majority of the facultatively pathogenic ciliate Uronema marinum within 1-2 days, providing a quantitative basis for developing predator-based biocontrol strategies in aquaculture. Genomic analysis shows that C. vorax possesses a highly fragmented macronuclear genome enriched with predation-related pathways, including calcium-mediated contractility, cellular proteolysis, toxin expulsion systems, among others. Transcriptomic profiling during predation events further demonstrates significant upregulation of genes involved in cytoskeletal remodeling, proteolytic activity, and cellular detoxification. Evolutionary analyses suggest that C. vorax has an extremely long evolutionary history, exceptionally high nucleotide diversity even among ciliates, and gene family expansions linked to predatory adaptation. Although the prey possesses certain defensive mechanisms (e.g. trichocysts), these are largely ineffective against short-term predation in closed aquatic environments. These findings provide fundamental insights into the molecular basis of predation in ciliates and suggest the potential utility of C. vorax in biocontrol applications targeting pathogenic ciliates.

Ciliophora↗
PubMed1992

Preferential expression of one beta-tubulin gene during flagellate development in Physarum.

The microbial eukaryote Physarum polycephalum displays several distinct cell types in its life cycle, including amoebae, flagellates and plasmodia. Despite its relative simplicity, Physarum has a tubulin gene family of complexity comparable to that of Drosophila. We have identified beta-tubulin cDNAs from Physarum that are derived from the betA beta-tubulin locus and encode beta 1A tubulin. We have also identified a partial cDNA for the unlinked betB beta-tubulin gene, which encodes beta 1B tubulin. The polypeptide sequences encoded by betA and betB show 99% identity, but the nucleotide sequences show only 85% identity, consistent with an ancient duplication of these genes. The betB gene is expressed in amoebae, flagellates and plasmodia, whereas betA is expressed only in amoebae and flagellates. During the amoeba-flagellate transition the level of betA transcript increases over 100-fold, while the level of betB transcript changes very little. Thus Physarum has a mechanism for regulating the level of discrete beta-tubulin transcripts differentially during flagellate development. A need for this differential regulation could account for the maintenance of the virtually isocoding betA and betB beta-tubulin genes.

Amino Acid Sequence↗
PubMed2025

Unisexual reproduction in the global human fungal pathogen Cryptococcus neoformans.

The human fungal pathogen Cryptococcus species complex (encompassing C. neoformans, C. deneoformans, and the C. gattii species complexes) exhibit diversity in sexual reproduction, including α-a mating, pseudosexual reproduction, as well as unisexual reproduction initiated from a single isolate or between isolates of the same mating type. A central conundrum is that while most Cryptococcus natural populations exhibit significant α mating-type bias, genetic and genomic analyses show recombination occurs in nature. The discovery of unisexual reproduction in C. deneoformans provided insight; however, thus far unisexual reproduction has never been directly observed in the predominant global pathogenic species C. neoformans. Here, we provide evidence that mutating the RIC8 gene, which encodes a conserved guanine nucleotide exchange factor (GEF) involved in both chaperoning and activating Gα proteins, enables unisexual reproduction in C. neoformans. Additionally, we show that genetic variation in the natural population promotes unisexual reproduction, and unisexual reproduction in C. neoformans involves canonical meiotic recombination. Finally, we found that deletion of both GPA2 and GPA3 in the MATα background leads to self-filamentation without sporulation, suggesting that differential modulation of the Gα proteins, likely involving Ric8, could underlie the switch between different modes of sexual reproduction in Cryptococcus. Our study further highlights that the highly conserved Ric8 GEF can act as an important regulator of cellular development in response to environmental stimuli and could modulate sexual reproduction in nature. We hypothesize that unisexual reproduction occurs much more frequently in nature than currently appreciated, and possibly in other fungi and microbial eukaryotes as well.

G protein↗
PubMed2025

Persistent gaps and errors in reference databases impede ecologically meaningful taxonomy assignments in 18S rRNA studies: a case study of terrestrial and marine nematodes.

In metabarcoding studies, Linnaean taxonomy assignments of Operational Taxonomic Units (OTUs) or Amplicon Sequence Variants (ASVs) underpin many downstream bioinformatics analyses and ecological interpretations of environmental DNA (eDNA) datasets. However, public molecular databases (i.e., SILVA, EUKARYOME, BOLD) for most microbial metazoan phyla (nematodes, tardigrades, kinorhynchs, etc.) are sparsely populated, negatively impacting our ability to assign ecologically meaningful taxonomy to these understudied groups. Additionally, the choice of bioinformatics parameters and computational algorithms can further impact the accuracy of eDNA taxonomy assignments. Here, we use two in-silico datasets to show that taxonomy assignments using the 18S rRNA gene can be dramatically improved by curating Linnaean taxonomy strings associated with each reference sequence and closing phylogenetic gaps by improving taxon sampling. Using free-living nematodes as a case study, we applied two commonly used taxonomy assignment algorithms (BLAST+ and the QIIME2 Naïve Bayes classifier) across six iterations of the SILVA 138 reference database to evaluate the precision and accuracy of taxonomy assignments. The BLAST+ top hit with a 90% sequence similarity cutoff often returned the highest percentage of correctly assigned taxonomy at the genus level, and the QIIME2 Naïve Bayes classifier performed similarly well when paired with a reference database containing corrected taxonomy strings. Our results highlight the urgent need for phylogenetically-informed expansions of public reference databases (encompassing both genomes and common gene markers), focused on poorly sampled lineages which are now robustly recovered via eDNA metabarcoding approaches. Additional taxonomy curation efforts should be applied to popular reference databases such as SILVA, and taxon sampling could be rapidly improved by more frequent incorporation of newly published GenBank sequences linked to genus and/or species level identifications.

18S rRNA metabarcoding↗
PubMed1978

Nonmutagenic action of cannabinoids in vitro.

Under the specific conditions reported for the separate tests delta9-tetrahydrocannabinol (THC) did not elicit a mutagenic response in microbial and eukaryotic in vitro test systems. THC treatment to histidine auxotrophs of Salmonella typhimurium strains TA 98 (susceptible to frame shift mutation) and TA 100 (susceptible to base pair substitution) were investigated. Analysis for possible revertance in the presence and absence of S9 microsomal activation system indicated an absence of induction of gene mutation. Cultured fibroblasts from healthy individuals and DNA repair deficient Xeroderma pigmentosum patients display similar survival activity upon exposure to THC. There was no observable increase in the number of chromosome breaks or chromatid exchanges following exposure to THC or THC plus S9 microsomal fraction. THC, 11-OHdelta9-THC, cannabinol, and cannabidiol did not induce unscheduled DNA repair synthesis in cultured human fibroblasts. Moreover, THC did not suppress UV-induced DNA repair synthesis.

Adult↗
PubMed2025

Concurrent stimulation of diflufenican biodegradation and changes in the active microbiome in gravel revealed by Total RNA.

The use of slowly degraded pesticides poses a particular problem when these are applied to urban areas such as gravel paths. The urban gravel provides an environment very different from agricultural soils; i.e., it is both lower in carbon and microbial activity. We, therefore, endeavored to stimulate the degradation of the pesticide diflufenican added to urban gravel microcosms amended with dry alfalfa to increase microbial activity. In the present study, alfalfa addition significantly increased the formation of diflufenican's primary metabolite, 2-[3-(trifluoromethyl)phenoxy]nicotinic acid (AE-B), indicating stimulated biotransformation. The concurrent changes of the active microbial communities within the gravel were explored using shotgun metatranscriptomic sequencing of ribosomal RNA and messenger RNA. Although bacterial taxa remained dominant (87.0%-98.5% relative abundance), the alfalfa treatment led to a 4-5-fold increase in eukaryotic groups, including fungi and microbial grazers. Several microbial taxa potentially involved in the degradation of complex carbon compounds and aromatic pollutants-including Bacteroidetes, Verrucomicrobia, Sordariomycetes, Mortierellales, Tremellales, Sphingopyxis, and Phenylobacterium-increased in relative abundance following alfalfa amendment. Functional gene profiling revealed elevated expression of genes related to microbial activity and biomass production. Genes with potential roles in the breakdown of complex carbon structures (e.g., xylanases/chitin deacetylases) and in the transformation of aromatic compounds (e.g., ring-cleaving dioxygenases) were revealed. We conclude that complex carbon amendments can enhance the microbial activity, promoting the biotransformation of diflufenican in urban gravel environments. These findings provide new insights into the interactions between microbial community dynamics, gene expression profiles, and pesticide biotransformation in non-agricultural matrices.IMPORTANCEPesticides used on urban areas, e.g., gravel paths, are likely to have different effects and fates than when these are used on agricultural soils. Hence, studies into the degradation of pesticides applied to urban matrices are needed. We have previously shown that metabolites of the persistent pesticide diflufenican are even more persistent in urban soils, and it has also previously been shown that these metabolites leach from gravel surfaces. The reasons behind this are that the urban gravel provides an environment very different from agricultural soils; i.e., it is both lower in carbon and microbial activity. In the present study, we, therefore, endeavored to stimulate the degradation of the pesticide diflufenican added to urban gravel microcosms amended with dry alfalfa to increase microbial activity, concurrently studying the changes in the active microbiome by Total RNA-metatranscriptomics.

Biodegradation, Environmental↗
PubMed1992

Development of a specific-locus assay in the ad-3 region of two-component heterokaryons of Neurospora: a review.

In recognition of the need for a more comprehensive data base for genetic risk assessment of human exposure to mutagenic agents in the environment, a model system was developed for specific-locus studies in Neurospora crassa. This lower eukaryotic organism permits the utilization of microbial techniques for recovery of large numbers of specific-locus mutations at two closely linked loci as well as their subsequent genetic analysis. In particular, this assay makes possible exploratory experiments with different environmental mutagens to obtain data on a wide variety of experimental conditions. Such data make it possible to study induction kinetics and mutational spectra in a manner that is not as yet feasible in higher eukaryotic organisms. The adenine-3 (ad-3) specific-locus assay was modeled after the 2-gene, morphological specific-locus assay in the dilute-short-ear region of the mouse, and it also detects forward-mutations at two closely linked loci, namely, ad-3A and ad-3B. Because ad-3 mutations are recovered by a direct method, based on the accumulation of a reddish-purple pigment in the vacuoles of the mycelium rather than their requirement for adenine, this system is both a morphological and biochemical specific-locus assay. The use of the ad-3 assay system in experiments with different environmental mutagens has provided precise dose-response curves not only for inactivation, but also the overall induction of ad-3 mutations. Genetic characterization of these ad-3 mutations by a series of 3 rapid and simple genetic tests permits the identification of 18 subclasses of gene/point mutations, and 12 subclasses of multilocus deletion mutations. These subclasses also include 3 different classes of multiple-locus mutations with separate sites of recessive lethal damage either in the immediately adjacent regions or elsewhere in the genome. In summary, this specific-locus assay provides a capability that is unique among eukaryotic organisms for the recovery and analysis of genetic damage at 2 closely linked loci.

Adenine↗
PubMed1992

Mechanism of C. trachomatis attachment to eukaryotic host cells.

A novel trimolecular mechanism of microbial attachment to mammalian host cells was characterized for the obligate intracellular pathogen Chlamydia trachomatis. Using purified glycosaminoglycans (GAGs) and specific GAG lyases, we demonstrated that a heparan sulfate-like GAG present on the surface of chlamydia organisms is required for attachment to host cells. These observations were supported by inhibition of attachment following binding of heparan sulfate receptor analogs to chlamydiae and by demonstrating that chlamydiae synthesize a unique heparan sulfate-like GAG. Furthermore, exogenous heparan sulfate, as an adhesin analog, restored attachment and infectivity to organisms that had lost these attributes following treatment with heparan sulfate lyase. These data suggest that a GAG adhesin ligand mediates attachment by bridging mutual GAG receptors on the host cell surface and on the chlamydial outer membrane surface.

Animals↗
PubMed1976

Carbon metabolism in model microbial systems from a temperate salt marsh.

The metabolism of a saltwater leachate of 14C-labeled Spartina alterniflora was examined in laboratory systems using mixed, salt marsh microbial communities and, by addition of appropriate antibiotics, communities with bacteria or eukaryotes inhibited. Label uptake was more rapid in the systems with bacteria alone and with the mixed microbial community than with fungi alone. Mineralization of the added label was more extensive in the mixed and bacterial systems, whereas the fungi appear more efficient at converting the label into particulate biomass. Particulate biomass production efficiencies ranged from a high of 0.82 for the fungal system to 0.21 in the mixed community, with the bacterial system giving an intermediate value of 0.54. The presence of protozoa and microcrustaceans in the mixed system appears to account for an increase in the mineralization of the label assimilated. Additional experiments with whole labeled Spartina, a leachate from Spartina, and Spartina after leaching revealed that the seawater-soluble portions of the plants were attacked most rapidly by the microbial community.

Animals↗