Biology subjects

Iniesto, M.

Publications and source records attributed to Iniesto, M..

3 recordsLinked to original sources

bioRxiv2026

Redox distribution of Asgard archaea and co-occurring taxa in microbial mats from an early Proterozoic ecosystem analog

Increasing evidence supports that eukaryotes originated from the symbiosis of an Asgard archaeon, the alphaproteobacterial ancestor of mitochondria, and possibly additional bacterial contributions. Eukaryogenesis likely occurred in redox-transition environments such as microbial mats or shallow sediments [~]2 billion years ago, when atmospheric oxygen was far lower than today, and oceans were euxinic. We investigated Asgardarchaeota-enriched microbial mats from the low-oxygen, sulfidic Catherine volcano lake (Afar region, Ethiopia), mimicking early Proterozoic conditions. 16S rRNA gene metabarcoding, metagenomics, and metagenome-assembled genome (MAG) analyses across redox-stratified layers of in situ and mesocosm-maintained mats revealed that Asgardarchaeota thrived in the sulfate-reduction zone, mainly co-occurring with Desulfurobacterota and Myxococcota, among others. Lokiarchaeia and Thorarchaeia were more abundant in deeper, anoxic layers. Within Heimdallarchaeia, Heimdallarchaeales were enriched in upper layers, correlating with oxygen-tolerant hydrogenase and sulfate-reduction genes, whereas Hodarchaeales were more relatively abundant in anoxic layers, correlating with methanogenesis. Although reactive-oxygen-species defense mechanisms were widespread in Asgardarchaeota MAGs, they lacked genes for aerobic respiration. These results support the hypothesis that Asgard archaea engaged primarily in syntrophic interactions with sulfate-reducers under conditions prevailing on the early Earth at the onset of eukaryogenesis.

microbiology↗

bioRxiv2023

Exploring the prokaryote-eukaryote interplay in microbial mats from an Andean athalassohaline wetland

Microbial community assembly results from the interaction between biotic and abiotic factors. However, environmental selection is thought to predominantly shape communities in extreme ecosystems. Salar de Huasco, situated in the high altitude Andean Altiplano, represents a poly-extreme ecosystem displaying spatial gradients of physicochemical conditions. To disentangle the influence of abiotic and biotic factors, we studied prokaryotic and eukaryotic communities from microbial mats and underlying sediments across contrasting areas of this athalassohaline ecosystem. The prokaryotic communities were primarily composed of bacteria, notably including a significant proportion of photosynthetic organisms like Cyanobacteria and anoxygenic photosynthetic members of Alpha- and Gammaproteobacteria and Chloroflexi. Additionally, Bacteroidetes, Verrucomicrobia, and Deltaproteobacteria were abundantly represented. Among eukaryotes, photosynthetic organisms (Ochrophyta, Archaeplastida) were predominant, alongside relatively abundant ciliates, cercozoans, and flagellated fungi. Salinity emerged as a key driver for the assembly of prokaryotic communities. Collectively, abiotic factors influenced both prokaryotic and eukaryotic communities, particularly those of algae. However, prokaryotic communities strongly correlated with photosynthetic eukaryotes, suggesting a pivotal role of biotic interactions in shaping these communities. Co-occurrence networks suggested potential interactions between different organisms, such as diatoms with specific photosynthetic and heterotrophic bacteria or with protist predators, indicating influences beyond environmental selection. While some associations may be explained by environmental preferences, the robust biotic correlations, alongside insights from other ecosystems and experimental studies, suggest that symbiotic and trophic interactions significantly shape microbial mat and sediment microbial communities in this athalassohaline ecosystem.

microbiology↗

bioRxiv2020

Reductive evolution and unique infection and feeding mode in the CPR predatory bacterium Vampirococcus lugosii

The Candidate Phyla Radiation (CPR) constitutes a large supergroup of mostly uncultured bacterial lineages discovered through metabarcoding and metagenomics in diverse environments. Having small cell sizes, reduced genomes, and limited biosynthetic capabilities, they are thought to be symbionts of other organisms from which they obtain essential biomolecules. However, the nature of this symbiosis (mutualistic, neutral, or parasitic) has been ascertained only for rare cultured members of the CPR phylum Saccharibacteria, which are epibiotic parasites of other bacteria. Here, we characterize the biology and the genome of Vampirococcus lugosii, which becomes the first described species of Vampirococcus, a genus of epibiotic bacteria morphologically identified decades ago. Vampirococcus belongs to the CPR phylum Absconditabacteria. It feeds on anoxygenic photosynthetic gammaproteobacteria, fully absorbing their cytoplasmic content. The cells divide epibiotically, forming multicellular stalks whose apical cells can more easily reach new hosts. Vampirococcus genome is small (1.3 Mbp) and highly reduced in biosynthetic metabolism genes. However, it is enriched in genes related to an elaborate, fibrous cell surface likely involved in complex interactions with the host. Comparative genomic analyses show that gene loss has been continuous during Absconditabacteria, and generally most CPR bacteria, evolution. Nonetheless, gene loss was compensated by gene acquisition by horizontal gene transfer and evolution de novo. In Vampirococcus, these innovations include new CRISPR-Cas effectors and a novel electron transport chain. Our findings confirm parasitism as a widespread lifestyle of CPR bacteria, which probably play a previously neglected virus-like ecological role in ecosystems, controlling bacterial populations by a unique form of predation.

microbiology↗