RESUMEN
CyanoHABs have substantial impacts on the functioning and sustainability of freshwater ecosystems by restricting light penetration, depleting dissolved oxygen, and producing various toxins. This study combined physicochemical variable measurements, 16S rRNA gene sequencing and microscopy observations to examine mechanisms that govern the assembly of bacterioplankton communities following the progress of cyanobacterial blooms in a freshwater reservoir. Throughout the sampling season, bacterioplankton distribution patterns were well predicted by a neutral model, which assumes passive dispersal and ecological drift as the predominate mechanisms for community assembly. The neutral model consistently explained the distribution of over 67% of bacterioplankton OTUs and its fit was weaker during the cyanobacterial blooms (R2 = 0.322) than the before- (R2 = 0.549) and after-bloom stages (R2 = 0.535). Variations of environmental factors, acting as selective pressures, explained shifts of non-neutral OTUs (above/under neutral prediction) (63.9%) better than neutral OTUs (34.5%). Co-occurrence network analysis organized microbial communities into modules and revealed strong positive correlations between bacterioplankton and cyanobacteria than with planktonic algae and zooplankton. Overall, our results suggest that neutral processes play significant roles in assembling bacterioplankton communities over a cyanobacterial bloom succession and its relative importance may be weakened by biotic pressures (interspecific interactions) during the bloom period. Our results also indicate that among biotic factors, cyanobacteria had greater impacts on bacterioplankton community assembly than planktonic algae and zooplankton.
Asunto(s)
Cianobacterias , Microbiota , Agua Dulce , Plancton , ARN Ribosómico 16SRESUMEN
This paper describes the selection of Schizosaccharomyces yeasts with adequate oenological suitability and high capacity for the degradation of malic acid. Despite the almost non-existent number of commercial strains, the use of this yeast genus has recently been recommended by the International Organisation of Vine and Wine (OIV, in French). Thus, in the present study, a large number of Schizosaccharomyces strains were isolated using a selective differential medium. Initially, classic parameters of oenological interest for the use of fermentative strains of Saccharomyces cerevisiae (the most frequently used type of yeast) were assessed. Only five strains of moderate acetic acid production lower than 0.4 g/L were obtained at the end of fermentation. Other, more specific features of this yeast genus' physiology were also studied, including urease activity and the production of pyruvic acid and glycerol. Finally, oenological suitability was determined by comparing selected strains with other Schizosaccharomyces reference and S cerevisiae control strains. Schizosaccharomyces strains produced 80% less urea content, four times higher pyruvic acid levels and 1 g higher glycerol contents than the Saccharomyces reference strains. The results confirmed that it is possible to perform selective processes on microorganisms from the genus Schizosaccharomyces using methodology developed in this work to obtain strains of industrial interest.