Strong reorganization of multi-domain microbial networks associated with primary producers sedimentation from oxic to anoxic conditions in an hypersaline lake

Abstract

Understanding the role of microbial interactions in the functioning of natural systems is often impaired by the levels of complexity they encompass. In this study, we used the relative simplicity of an hypersaline crater lake hosting only microbial organisms (Dziani Dzaha) to provide a detailed analysis of the microbial networks including the three domains of life. We identified two main ecological zones, one euphotic and oxic zone in surface, where two phytoplanktonic organisms produce a very high biomass, and one aphotic and anoxic deeper zone, where this biomass slowly sinks and undergoes anaerobic degradation. We highlighted strong differences in the structure of microbial communities from the two zones and between the microbial consortia associated with the two primary producers. Primary producers sedimentation was associated with a major reorganization of the microbial network at several levels: global properties, modules composition, nodes and links characteristics. We evidenced the potential dependency of Woesearchaeota to the primary producers’ exudates in the surface zone, and their disappearance in the deeper anoxic zone, along with the restructuration of the networks in the anoxic zone toward the decomposition of the organic matter. Altogether, we provided an in-depth analysis of microbial association network and highlighted putative changes in microbial interactions supporting the functioning of the two ecological zones in this unique ecosystem.

Phytoplanktonic species in the haloalkaline Lake Dziani Dzaha select their archaeal microbiome

“…This counter-intuitive observation advocates for a high selectivity in A. fusiformi phycosphere and the possible lack of a specific P. salinarum phycosphere for which the detected microbiome might only reflect the free-living communities in the vicinity of the cells. The hypothesis of an absence of a P. salinarum phycosphere by Escalas et al (2021) was congruent with predictions suggesting that chemotactic associations could not be detected for phytoplanktonic cells smaller than 4 μm (J. R. Seymour et al, 2017). However, associations between taxa identified using CMN correspond to statistical relationships that are observed at a relatively large observational scale compared with the scale at which microbial interactions do actually occur, being relevant for the phycosphere study.…”

“…The hypothesis of an absence of a P. salinarum phycosphere by Escalas et al. (2021) was congruent with predictions suggesting that chemotactic associations could not be detected for phytoplanktonic cells smaller than 4 μm (J. R. Seymour et al., 2017). However, associations between taxa identified using CMN correspond to statistical relationships that are observed at a relatively large observational scale compared with the scale at which microbial interactions do actually occur, being relevant for the phycosphere study.…”

“…), the microbiome associated with the dominant phytoplanktonic species, A. fusiformi and P. salinarum has not been identified yet. Despite much larger size, A. fusiformi (filaments average length 335 μm [min 170 μm ‐ max 2390 μm] (Cellamare et al., 2018)) appears to co‐occur with a very limited number of archaeal and bacterial taxa (OTUs) compared to P. salinarum (diameters from 2.5 to 4.5 μm (Cellamare et al., 2018)), according to co‐occurrence microbial networks (CMN) (Escalas et al., 2021). This counter‐intuitive observation advocates for a high selectivity in A. fusiformi phycosphere and the possible lack of a specific P. salinarum phycosphere for which the detected microbiome might only reflect the free‐living communities in the vicinity of the cells.…”

“…Here, we used a cell‐level observational scale, based on flow cytometry cell‐sorting, to test the existence of specific phycospheric microbiomes (i.e. particle‐attached), hypothesized previously at larger scale (Escalas et al., 2021), for the two‐codominant phytoplanktonic species, A. fusiformi and P. salinarum , retrieved in the same ecosystem, Lake Dziani Dzaha. We investigated the diversity of bacterial, microeukaryotic and archaeal communities retrieved within the phycosphere of the two primary producers to test whether these two phytoplanktonic species harbour specific phycospheric microbiomes.…”

Metagenome-based Exploration of Bacterial Communities Associated with Cyanobacteria Strains Isolated from Thermal Muds

“…This tight physical relationship with cyanobacteria suggests close interactions with cyanobacterial surface components. Besides, the presence of bacteria that are directly attached or immediately adjacent to cyanobacterial cells suggests the possibility of intense and/or specific nutrient exchanges between these microorganisms as it has been observed in other microbial communities dominated by certain cyanobacteria [44].…”