The composition of wine yeast populations, present during spontaneous fermentation of musts from two wine‐producing areas of Greece (Amyndeon and Santorini) and followed for two consecutive years, were studied using a range of molecular techniques. Internal Transcribed Spacer (ITS) ribotyping was convincingly applied for yeast species identification, proving its usefulness as a reliable tool for the rapid characterization of species composition in yeast population studies. Restriction Fragment Length Polymorphism (RFLP) of mitochondrial DNA (mtDNA) was shown to be a convenient criterion for the detection of intraspecies genetic diversity of both Saccharomyces and non‐Saccharomyces isolate populations. Similarly, polymorphism of amplified δ interspersed element sequences provided an additional criterion for S. cerevisiae strain differentiation. Comparative analysis of S. cerevisiae genetic diversity, using mtDNA restriction patterns and δ‐amplification profiles, showed a similar discriminative power of the two techniques. However, by combining these approaches it was possible to distinguish/characterize strains of the same species and draw useful conclusions about yeast diversity during alcoholic fermentation. The most significant findings in population dynamics of yeasts in the spontaneous fermentations were (i) almost complete absence of non‐S.cerevisiae species from fermentations of must originating from the island Santorini, (ii) a well recorded strain polymorphism in populations of non‐Saccharomyces species originating from Amyndeon and (iii) an unexpected polymorphism concerning S. cerevisiae populations, much greater than ever reported before in similar studies with wine yeasts of other geographical regions.

The complete sequence of the apiculate wine yeast Hanseniaspora uvarum mtDNA has been determined and analysed. It is an extremely compact linear molecule containing the shortest functional region ever found in fungi (11 094 bp long), flanked by Type 2 telomeric inverted repeats. The latter contained a 2704-bp-long subterminal region and tandem repeats of 839-bp units. In consequence, a population of mtDNA molecules that differed at the number of their telomeric reiterations was detected. The functional region of the mitochondrial genome coded for 32 genes, which included seven subunits of respiratory complexes and ATP synthase (the genes encoding for NADH oxidoreductase subunits were absent), two rRNAs and 23 tRNA genes which recognized codons for all amino acids. A single intron interrupted the cytochrome oxidase subunit 1 gene. A number of reasons contributed towards its strikingly small size, namely: (1) the remarkable size reduction (by >40%) of the rns and rnl genes; (2) that most tRNA genes and five of the seven protein-coding genes were the shortest among known yeast homologs; and (3) that the noncoding regions were restricted to 5.1% of the genome. In addition, the genome showed multiple changes in the orientation of transcription and the gene order differed drastically from other yeasts. When all protein coding gene sequences were considered as one unit and were compared with the corresponding molecules from all other complete mtDNAs of yeasts, the phylogenetic trees constructed robustly supported its placement basal to the yeast species of the 'Saccharomyces complex', demonstrating the advantage of this approach over single-gene or multigene approaches of unlinked genes.

Glacier-fed streams (GFSs) are extreme and rapidly vanishing ecosystems, and yet they harbor diverse microbial communities. Although our understanding of the GFS microbiome has recently increased, we do not know which microbial clades are ecologically successful in these ecosystems, nor do we understand potentially underlying mechanisms. Ecologically successful clades should be more prevalent across GFSs compared to other clades, which should be reflected as clade-wise distinctly low phylogenetic turnover. However, methods to assess such patterns are currently missing. Here we developed and applied a novel analytical framework, “phyloscore analysis”, to identify clades with lower spatial phylogenetic turnover than other clades in the sediment microbiome across twenty GFSs in New Zealand. These clades constituted up to 44% and 64% of community α-diversity and abundance, respectively. Furthermore, both their α-diversity and abundance increased as sediment chlorophyll a decreased, corroborating their ecological success in GFS habitats largely devoid of primary production. These clades also contained elevated levels of putative microdiversity than others, which could potentially explain their high prevalence in GFSs. This hitherto unknown microdiversity may be threatened as glaciers shrink, urging towards further genomic and functional exploration of the GFS microbiome.

No abstract

No abstract