Search

International audience

International audience

In recent years resulting investigations in living microbialites have provided significant data that have been critical to disentangle the role of the various biotic and abiotic processes contributing to their development. Despite these efforts separating the impact and magnitude of these processes remain a difficult task. At present the Maquinchao Basin in northeastern Patagonia, Argentina, contains both fossil and living microbialites. Thus, the region provides a unique opportunity to investigate the impact of intrinsic and extrinsic parameters in carbonate precipitation. Early investigations (Austral summer 2011) in living microbialites concluded that organomineralization was related to both photosynthetic activity in the more surficial layer (green), and sulfate-reduction in the lower part (beige). Field investigations in the same area four years later showed that the pounds previously containing abundant active mats had dried out, and in general revealed the absence of globular structured clusters of minerals in the microbial mats. Here we present microscale investigations using optical microscopy and SEM along with the 16SrRNA gene sequence diversity, and the physico-chemical parameters of the hosting waters. They were carried out in successive seasonal samplings in November 2015, April-May 2016, August 2016, February 2017, and March 2018. All microbialite samples show regular occurrences of sulfate reducing bacteria (SRB) along with filaments of unknown origin. Carbonates are observed associated with erect filaments in shallow and active running water locations whereas the mineral phase is located below organic matter film in comparatively deeper and calmer water areas. Additionally, seasonal changes in the physicochemical properties of the hosting waters indicate that extrinsic parameters, especially evaporation, might play a more substantial role in the precipitation of these carbonates than previously proposed. The environmental differences between 2011 and 2015 in meteorological conditions, regional volcanic activity and associated deposits in the basin are analyzed. We concluded that they are likely responsible of the decrease of the mineralization processes, and particularly those associated with photosynthetic activity. These results call for caution when interpreting the degree of biological impact on the formation of microbialites in the geological record. Local extrinsic factors might have a changeable impact over time switching mineral precipitation from biotic to abiotic and vice-versa, which can be undistinguishable in fossilized microbialites., Latin American Journal of Sedimentology and Basin Analysis, 28 (2)

Understanding the response of geo- and biosystems to past climatic disturbance is primordial to assess the short to long terms effects of current global change. Lacustrine sediments are commonly used to investigate the impact of climatic change on biogeochemical cycling. In these sediments, subsurface microbial communities play a primordial role in nutrient, organic matter and elemental cycling, but they also can affect the sedimentary record and overprint the original paleoenvironmental signal. Subsurface microbial communities have therefore been investigated to assess the potential connection between microbial diversity and environmental change. Lake Ohrid (North Macedonia, Albania) is the oldest lake in Europe and has been the target of a scientific deep drilling in 2013. The upper 447 m of the 584-m-long sedimentary drill core record obtained from the central part of the lake (DEEP site) is composed of clayey to silty-clayey lithologies differing substantially in terms of carbonate and organic matter content between glacials and interglacials. We investigated the microbial diversity in the retrieved sediment using 16S rRNA gene sequences along the upper ca. 200 m of the DEEP site record spanning ca. 515 ka to assess whether subsurface microbial communities were following a similar trend. Results show that Atribacteria, Betaproteobacteria, Bathyarchaeota and to a lower extent Dehalococcoidia phyla structured the community but their occurrence appears to be independent from each other. Atribacteria and Bathyarchaeota together with Dehalococcoidia are commonly encountered in deep lacustrine and marine sediments. Their metabolic versatility is adapted to low energy environments where they can realize the fermentation of various substrates (sugars, propionate and amino acids). The generation of H2 from Atribacteria and other fermenters can be used by Dehalococcoidia and Bathyarchaeota for acetogenesis, and even for chemolithoautrophic processes suggested at greater depths. Betaproteobacteria-associated sequences were often co-occurring with cyanobacterial sequences that suggest preservation of ancient DNA from the water column or catchment, down to at least 340 ka. In particular, fossil DNA from Cyanobacteria in dry glacial intervals may be the relict of ancient blooms of N-fixing clades in periods of nitrogen depletion. We compared the richness and diversity of all phylotypes with environmental parameters measured in corresponding intervals to test for the relationship between paleoenvironmental conditions, climatic modes and the subsurface biosphere. We found no significant relationship between any phylotype and measured environmental parameters, nor with sediment age or climate patterns. Our preliminary results support a weak recording of early diagenetic processes and their actors by bulk prokaryotic sedimentary DNA in Lake Ohrid, which might suggest dominant turnover and replacement by specialized low-energy clades of the deep biosphere.

International audience; The present context of health crisis and unprecedented lockdown is an opportunity for thinking, position-taking, indignation and controversy. As a social activity, work redefines itself every day, according to circumstances. Work specialists, ergonomists included, observe and reflect. Contrary to certain preconceived ideas, Ergonomics is not primarily about so-called “ergonomic” chairs, desks or toothbrushes. Work is a central object of ergonomics, and the technical resources associated with it cover only some of the questions it raises. The ergonomic project consists of perceiving this Work; and above and beyond the technical resources, it is the values, skills, relationships, organizations, etc. that are its pivotal components, as is its inclusion in society, and therefore in the lives of each and every one of us.; En un contexto excepcional de confinamiento que ha llevado a un cambio en la vida personal y profesional de todos, la SELF inició la redacción de un texto, cuyo objetivo es contribuir a reflexiones y debates dentro de la comunidad de ergónomos y ergónomas, y en general de la sociedad. Contrariamente a ciertas ideas preconcebidas, la ergonomía no consiste principalmente en el diseño de sillas, escritorios o cepillos de dientes "ergonómicos". El trabajo es un objeto central de la ergonomía, y los recursos técnicos asociados con él cubren solo algunas de las preguntas que éste plantea. El proyecto ergonómico consiste en percibir este Trabajo más allá de los aspectos técnicos: los valores, habilidades, relaciones, organizaciones, etc. que son sus componentes fundamentales, como lo es su inclusión en la sociedad y, por lo tanto, en la vida de todos y cada uno de nosotros.

Lacustrine sediments are widely used to investigate the impact of climatic change on biogeochemical cycling. In these sediments, subsurface microbial communities are major actors of this cycling but can also affect the sedimentary record and overprint the original paleoenvironmental signal. We therefore investigated the subsurface microbial communities of the oldest lake in Europe, Lake Ohrid (North Macedonia, Albania), to assess the potential connection between microbial diversity and past environmental change using 16S rRNA gene sequences. Along the upper ca. 200 m of the DEEP site sediment record spanning ca. 515 thousand years (ka), our results show that Atribacteria, Bathyarchaeia and Gammaproteobacteria structured the community independently from each other. Except for the latter, these taxa are common in deep lacustrine and marine sediments due to their metabolic versatility adapted to low energy environments. Gammaproteobacteria were often co-occurring with cyanobacterial sequences or soil-related OTUs suggesting preservation of ancient DNA from the water column or catchment back to at least 340 ka, particularly in dry glacial intervals. We found significant environmental parameters influencing the overall microbial community distribution, but no strong relationship with given phylotypes and paleoclimatic signals or sediment age. Our results support a weak recording of early diagenetic processes and their actors by bulk prokaryotic sedimentary DNA in Lake Ohrid, replaced by specialized low-energy clades of the deep biosphere and a marked imprint of erosional processes on the subsurface DNA pool of Lake Ohrid.