Biology subjects

Sieracki, M. E.

Publications and source records attributed to Sieracki, M. E..

3 recordsLinked to original sources

bioRxiv2024

Global population structure of a unicellular marine predator

Unicellular predators, especially marine heterotrophic flagellates (HFs), are fundamental to marine food webs, facilitating the flow of nutrients from bacteria and the smallest primary producers to upper trophic levels. Comprehending their distributions and diversity is essential for understanding the functioning of marine ecosystems. The uncultured MArine STramenopiles clade 4 (MAST-4) constitutes a crucial HF member of the ocean microbiome with a predatory (bacterivorous) lifestyle. Temperature gradients have influenced the evolution and biogeography of MAST-4 species. Yet, similarly to most uncultured microbes, there is limited information on the population diversity and structure within MAST-4 species. This information is key for better comprehending the ecological roles and adaptations of different MAST-4 species to specific ocean niches. Here, we investigate the population diversity and structure on the global scale of the MAST-4 species A, B, C, and E by combining metagenomics and single-cell genomics data from the Tara Oceans expedition. We found substantial population divergence in the abundant MAST-4A and C species, while lower levels of divergence were observed in species B and E. Temperature and salinity were the main drivers structuring the populations within the four MAST-4 species. The analysis of positively selected gene clusters within each MAST-4 species revealed genomic areas likely the basis of population adaptation to different niches. Overall, our results contribute to a better comprehension of the population diversity and structure of four species belonging to an important group of unicellular predators, offering insights into their ecological roles and adaptations in the global ocean. The results also contribute to understanding microbial populations, a dimension of diversity that remains poorly known for most wild species and is pivotal in global change.

ecology↗

bioRxiv2020

Evolutionary diversification of tiny ocean predators

Unicellular eukaryotic predators have a crucial role in the functioning of the ocean ecosystem by recycling nutrients and energy that are channeled to upper trophic levels. Traditionally, these evolutionary-diverse organisms have been combined into a single functional group (Heterotrophic flagellates), overlooking their organismal differences. Here we investigate four evolutionary related species belonging to one cosmopolitan family of uncultured marine picoeukaryotic predators: MAST-4 (species A, B, C, and E). Co-occurrence and distribution analyses in the global surface ocean indicated contrasting patterns in MAST-4A & C, suggesting adaptation to different temperatures. We then investigated whether these spatial distribution patterns were mirrored by MAST-4 genomic content using Single-Cell Genomics. Analyses of 69 single-cells recovered 66-83% of the MAST-4A/B/C/E genomes, which displayed substantial inter-species divergence. MAST-4 genomes were similar in terms of broad gene functional categories, but they differed in enzymes of ecological relevance, such as glycoside hydrolases (GHs), which are part of the food degradation machinery in MAST-4. Interestingly, MAST-4 species featuring a similar GH composition co-excluded each other (A & C) in the surface global ocean, while species with a different set of GHs appeared to be able to co-exist (species B & C) suggesting further niche diversification associated to prey digestion. We propose that differential niche adaptation to temperature and prey type has promoted adaptive evolutionary diversification in MAST-4. Altogether, we show that minute ocean predators from the same family may have different biogeography and genomic content, which need to be accounted to better comprehend marine food webs.

ecology↗

bioRxiv2020

Mediocremonas mediterraneus, a New Member within the Developea

The Stramenopiles are a large and diverse group of eukaryotes that possess various lifestyles required to thrive in a broad array of environments. The stramenopiles branch with the alveolates, rhizarians, and telonemids, forming the supergroup TSAR. Here, we present a new genus and species of aquatic nanoflagellated stramenopile: Mediocremonas mediterraneus, a free-swimming heterotrophic predator. M. mediterraneus cell bodies measure between 2.0-4.0 m in length and 1.2-3.7 m in width, possessing two flagella and an oval body morphology. The growth and grazing rate of M. mediterraneus in batch cultures ranges from 0.68 to 1.83 d-1 and 1.99 to 5.38 bacteria h-1, respectively. M. mediterraneus was found to be 93.9% phylogenetically similar with Developayella elegans and 94.7% with Develorapax marinus, two members within the class Developea. The phylogenetic position of the Developea and the ability of M. mediterraneus to remain in culture makes it a good candidate for further genomic studies that could help us to better understand phagotropy in marine systems as well as the transition from heterotrophy to phototrophy within the stramenopiles.

microbiology↗