Freshwater bacterial diversity, functions and stability.

Biodiversity is declining worldwide with detrimental effects on ecosystems functions and services that it sustains. The relationship between biodiversity and freshwater purification remains unclear. Freshwater purification is of paramount importance for humankind as eighty percent of the worlds population is exposed to high levels of threat in terms of water security. Bacteria are the most diverse and abundant organisms on Earth and they play, directly or indirectly, a key role in the majority of ecosystem services including water purification. The current work aimed, in freshwater systems, to unravel the relationships between microbial diversity and: (a) biodegradation of toxic compounds (i.e. specialised function); (b) respiration (i.e. broad function) and; (c) stability of broad functioning. Firstly, preliminary experiments were carried out to establish freshwater sample size to representatively evaluate bacterial communities diversity and also suitable natural and man-made toxic compounds for freshwater incubation experiments. Then, the microbial communities ability to degrade microcystin-LR was explored in the context of previous exposures and nutrient availability. Finally, we focused on the relationships between diversity and functioning. A decrease in microbial diversity caused a decrease in both broad and specialised ecosystem functions tested. Stability of broad functioning was also negatively affected by a decrease in microbial diversity. Both lakes (Scotland) and rivers (Australia) microcosms experiments resulted in comparable findings suggesting consistent relationships across different freshwater systems. These results highlight that, similarly to macro-organisms (plant and animals), declining diversity of the microbial communities has direct consequences for important ecosystem functioning and services and therefore, microbial diversity should be explicitly considered in all biodiversity conservation debates

Lack of functional redundancy in the relationship between microbial diversity and ecosystem functioning.

1. Biodiversity is declining worldwide with detrimental effects on ecosystems. However, we lack a quantitative understanding of the shape of the relationship between microbial biodiversity and ecosystem function (BEF). This limits our understanding of how microbial diversity depletion can impact key functions for human well-being, including pollutant detoxification. 2. Three independent microcosm experiments were conducted to evaluate the direction (i.e. positive, negative or null) and the shape of the relationships between bacterial diversity and both broad (i.e. microbial respiration) and specialized (i.e. toxin degradation) functions in five Australian and two UK freshwater ecosystems using next-generation sequencing platforms. 3. Reduced bacterial diversity, even after accounting for biomass, caused a decrease in broad (i.e. cumulative microbial respiration) and specialized (biodegradation of two important toxins) functions in all cases. Unlike the positive but decelerating BEF relationship observed most frequently in plants and animals, most evaluated functional measurements were related to bacterial diversity in a non-redundant fashion (e.g. exponentially and/or linearly). 4. Synthesis. Our results suggest that there is a lack of functional redundancy in the relationship between bacterial diversity and ecosystem functioning; thus the consequences of declining microbial diversity on ecosystem functioning and human welfare have likely been considerably underestimated

Bacterial communities' response to microcystins exposure and nutrient availability : linking degradation capacity to community structure

Eutrophication of freshwater bodies followed by cyanobacterial bloom and toxin production is an important issue in freshwater supply in both developed and developing countries. The primary mechanism for microcystins (MCs) (the main class of cyanobacterial toxins) dissipation is microbial degradation. Repeated exposure of freshwater bodies to cyanobacterial toxins MCs may affect indigenous microbial communities and may also enhance biodegradation of MCs, but the factors driving this relationship remain unclear. Six Scottish freshwater bodies with different histories of natural exposure to MCs and ability to degrade MC-LR (the most common microcystin) were chosen as case study. Terminal Restriction Fragment Length Polymorphism (T-RFLP) and Biolog EcoPlate™ were used to study the structure and physiology of the bacterial communities. Previous exposure to MCs significantly contributed to the bacterial communities shape and microbial physiology of the water bodies under study. Other factors that significantly affected the bacterial communities were dissolved organic carbon and concentration of nitrogen compounds as well as temperature. Moreover a significant relationship was found between bacterial communities' structure and MC-LR half-life. These data suggest that exposure to MCs drives changes in structure and physiology of bacterial communities and in turn those communities differentially perform degradation of MC-LR

FEMS Yeast Res

The yeast Candida zemplinina (Starmerella bacillaris) is frequently isolated from grape and wine environments. Its enological use in mixed fermentation with Saccharomyces cerevisiae has been extensively investigated these last few years, and several interesting features including low ethanol production, fructophily, glycerol and other metabolites production, have been described. In addition, molecular tools allowing the characterization of yeast populations have been developed, both at the inter- and intraspecific levels. However, most of these fingerprinting methods are not compatible with population genetics or ecological studies. In this work, we developed 10 microsatellite markers for the C. zemplinina species that were used for the genotyping of 163 strains from nature or various enological regions (28 vineyards/wineries from seven countries). We show that the genetic diversity of C. zemplinina is shaped by geographical localization. Populations isolated from winemaking environments are quite diverse at the genetic level: neither clonal-like behaviour nor specific genetic signature were associated with the different vineyards/wineries. Altogether, these results suggest that C. zemplinina is not under selective pressure in winemaking environments