In situ proteo-metabolomics reveals metabolite secretion by the acid mine drainage bio-indicator, Euglena mutabilis

Abstract

Euglena mutabilis is a photosynthetic protist found in acidic aquatic environments such as peat bogs, volcanic lakes and acid mine drainages (AMDs). Through its photosynthetic metabolism, this protist is supposed to have an important role in primary production in such oligotrophic ecosystems. Nevertheless, the exact contribution of E. mutabilis in organic matter synthesis remains unclear and no evidence of metabolite secretion by this protist has been established so far. Here we combined in situ proteo-metabolomic approaches to determine the nature of the metabolites accumulated by this protist or potentially secreted into an AMD. Our results revealed that the secreted metabolites are represented by a large number of amino acids, polyamine compounds, urea and some sugars but no fatty acids, suggesting a selective organic matter contribution in this ecosystem. Such a production may have a crucial impact on the bacterial community present on the study site, as it has been suggested previously that prokaryotes transport and recycle in situ most of the metabolites secreted by E. mutabilis. Consequently, this protist may have an indirect but important role in AMD ecosystems but also in other ecological niches often described as nitrogen-limited.

Dynamic substrate preferences predict metabolic properties of a simple microbial consortium

“…With the development of exometabolomics pipelines, the metabolic connections between microbes have begun to be studied at a large scale and have allowed for a more comprehensive approach to monitoring the dynamic transformations of relatively complex mixtures of substrates [5]. Some key examples include optimizing multiple steps of lignocellulose degradation [6, 7], understanding metabolic interactions between species in mixed communities [8], and determining the ecological role of individuals within a mixed community [9–11]. We have recently found exometabolite niche partitioning in two soil environments where sympatric microbes were found to target largely non-overlapping portions of the available substrates, thus minimizing substrate competition [10].…”

Metabolites Associated with Adaptation of Microorganisms to an Acidophilic, Metal-Rich Environment Identified by Stable-Isotope-Enabled Metabolomics

“…Untargeted metabolomics has tremendous potential for hypothesis generation in microbial communities since it provides a direct biochemical observation of the community metabolism. However, only a few studies (e.g., see reference 7) have used untargeted metabolomics to study adaptation to environmental challenges in a community context. This is in part because metabolomics methods are still challenging (relative to the more standardized omics approaches such as transcriptomics) due to a wide range of experimental complexities often associated with the environmental matrix (e.g., abundant salt can result in extensive experimental artifacts).…”

Arsenite response in Coccomyxa sp. Carn explored by transcriptomic and non‐targeted metabolomic approaches

“…Previous results revealed a similar behaviour in the arsenic hyper‐tolerant protist E. mutabilis , i.e. a lower arsenic accumulation in comparison to E. gracilis and a very low accumulation of arsenic methylated forms (Halter et al ., ). This suggests that, despite their ability to methylate arsenic, these arsenic hyper‐tolerant protists seem to favour other defence mechanisms such as preventing the accumulation of arsenic.…”

“…In particular, the total fatty acids composition of E. mutabilis is modified in response to arsenite, leading to an increased membrane fluidity, i.e. a higher unsaturation index (Halter et al ., ). By contrast, we did not observe such phenomenon with Coccomyxa sp.…”