Biology subjects

Elkassas, S. M.

Publications and source records attributed to Elkassas, S. M..

3 recordsLinked to original sources

bioRxiv2026

Beyond the Plastisphere: Phylogenetic and Biogeographic Diversity of Marine Microorganisms with Putative Plastic-Degradation Potential

Plastic pollution is widespread in marine environments, yet the diversity of microorganisms and enzymes that may contribute to plastic degradation remains poorly understood. To identify promising candidates for future experimental studies, we investigated marine microorganisms with proteins related to enzymes previously associated with plastic degradation. Using PlasticDB and the NCBI RefSeq protein database, we identified 523 distinct protein sequences from microorganisms with documented marine provenance. We then examined their evolutionary relationships, environmental origins, and geographic distributions to assess how these candidate proteins are distributed across marine microbial diversity. Only 10.3% of the curated sequence assignments originated from plastisphere or marine-biofilm records, while most were associated with other marine environments, particularly marine hosts. These findings suggest that searches focused exclusively on plastic-associated biofilms may overlook a substantial portion of the marine microbial diversity relevant to plastic transformation. The identified proteins include candidates for direct polyester hydrolysis as well as proteins that may contribute to oxidative chemistry or cellular protection during plastic-associated metabolism. Together, these phylogenetic and biogeographic analyses establish a targeted resource for the discovery and isolation of marine-derived genes with potential roles in plastic transformation, providing experimentally tractable candidates for biochemical characterization and future development of microbial and enzyme-based plastic recycling strategies.

microbiology↗

bioRxiv2026

Microbial Growth in an Enceladus Ocean Analog Medium Informed by Mineral Stability Modeling

Evidence from the Cassini mission confirmed that Saturns moon Enceladus hosts a subsurface alkaline ocean where rock-water reactions may generate redox disequilibria capable of supporting microbial metabolisms. To investigate potential microbial survival under simulated Enceladus ocean conditions, we used thermodynamic modeling to develop a salt formulation consistent with one possible Enceladus ocean composition and supplemented it with putative microbial energy sources to create a growth medium. The medium was inoculated with samples from diverse ocean world analog environments on Earth to determine which microorganisms could persist under Enceladus-like conditions. The microorganisms persisting in this geochemically bounded medium were heterotrophic, metabolically versatile bacteria with low carbon requirements. Genomic and physiological analyses further showed the presence of multiple stress-response pathways, sodium-based bioenergetic systems, osmoregulation strategies, and other adaptations consistent with survival in alkaline, low-nutrient settings. These results suggest that some stress-tolerant heterotrophic bacteria may serve as useful model organisms for life in Enceladus subsurface ocean. These findings demonstrate the value of geochemically modeled media as a framework for constraining habitability, identifying relevant biosignatures, and probing potential microbial survival strategies beyond Earth.

microbiology↗

bioRxiv2025

Metabolic and Population Profiles of Active Subseafloor Autotrophs in Young Oceanic Crust at Deep-Sea Hydrothermal Vents

At deep-sea hydrothermal vents, magmatically driven rock-water reactions in the crust generate gases and other reduced compounds that subseafloor microorganisms use for chemolithoautotrophy. In this study, microbial autotrophs from three diffuse flow hydrothermal vents at Axial Seamount in 2013 and 2014 were isotopically labeled using RNA Stable Isotope Probing (RNA-SIP), targeting subseafloor autotrophic mesophiles (30{degrees}C), thermophiles (55{degrees}C), and hyperthermophiles (80{degrees}C). We constructed taxonomic and functional profiles of active chemolithoautotrophs, examined population distributions across sites, and linked primary producers to their specific metabolic strategies within the subseafloor community. Dominant autotrophs exhibited hydrogen-dependent dissimilatory metabolisms such as sulfur and nitrate reduction and methanogenesis, as well as microaerophilic sulfide oxidation even at 80{degrees}C, consistent with fluid chemistries at each site. While hydrogenotrophic methanogenic archaea such as Methanothermococcus were restricted in their distribution and activity, hydrogenotrophic sulfur and nitrate reducers from the Aquificota (Thermovibrio), Campylobacterota (Nautiliaceae, Hydrogenimonas, and Desulfurobacteriaceae) were consistently active and present at all sites and years at both the population and community levels. Hydrogenase transcripts were significantly differentially expressed, and diverse hydrogenases were found in metagenome-assembled genomes of Aquificota members, highlighting the importance and versatility of their hydrogen utilization strategies which likely contribute to their cosmopolitan distribution across geochemically disparate subseafloor sites. Together, this study provides new insights into the functional dynamics and distribution of key subseafloor autotrophic microbial communities in young oceanic crust at deep-sea hydrothermal vents. IMPORTANCEDeep-sea hydrothermal vents are hotspots for life in the dark ocean, where rich animal ecosystems are supported by microbial primary producers utilizing the abundant chemical energy supplied by high-temperature water-rock reactions. Despite increasing knowledge about the geochemistry and microbiology of deep-sea hydrothermal vents, there is still a gap in our understanding of the key microbial players who fix much of the carbon at these sites, especially in the productive subseafloor. In this study, stable isotope probing was used to label active microbial autotrophs in diffuse flow venting fluids from three sites over two years and was combined with metatranscriptomic sequencing to identify their specific metabolic strategies. This research highlights the microbial community composition, function, gene regulation, and population dynamics that enable hydrothermal ecosystems to persist.

microbiology↗