Projects

Phytoplankton contributes significantly to marine primary productivity (MPP) and plays a key role in carbon sequestration via the biological carbon pump (BCP). Diatoms, a major phytoplankton group, account for ~25% of MPP and are critical to BCP due to their silicified cell walls, which act as mineral ballast. Viral infections are a key factor influencing BCP and carbon export efficiency (CEE). Viruses exhibit dual roles in marine ecosystems: they may enhance carbon export via the "viral shuttle" mechanism by promoting the formation of sinking aggregates or reduce it via the "viral shunt," which redirects organic carbon to dissolved organic matter (DOM) for microbial respiration. The interplay between these mechanisms depends on environmental and biological factors, including phytoplankton physiology, microbial community composition, and water column properties. However, the mechanisms by which viral infections influence phytoplankton aggregation and subsequent microbial processing of particulate organic matter remain poorly understood. The project Viral Infection-Driven Changes in Phytoplankton Aggregates and Their Microbial Processing (VIRAMP) investigates how viral infections shape the formation, composition, and fate of phytoplankton aggregates, focusing on microbial processes within aggregates and their impact on BCP and CEE in marine ecosystems. Prior studies show viral infections alter DOM quality, supporting distinct microbial communities and processes, with effects varying by virus type. While microbial processes in phytoplankton aggregates have been studied, their link to viral infections remains unexplored. This project aims to bridge this gap by integrating laboratory experiments, field studies, and advanced modelling to elucidate how viral infections modify the physical, chemical, and microbiological properties of aggregates, thereby affecting marine carbon cycling. The research will focus on diatoms and diatom viruses from our culture collection, with the potential
inclusion of haptophyte systems. Fieldwork will target the Northern Adriatic Sea, a productive, shallow, and well-mixed coastal system, where viral impacts on carbon cycling remain understudied compared to oceanic environments. We hypothesize that i) virus-infected phytoplankton aggregates support distinct microbial communities with altered functional traits compared to aggregates from healthy, senescing diatom cultures, and ii) biochemical properties, elasticity, and viscosity of infected aggregates differ from healthy ones, influencing microbial processing in the water column and CEE. To test these hypotheses, we will analyse differences between aggregates from healthy and infected phytoplankton populations (lab cultures and environmental samples), their physicochemical properties, and their support for microbial growth, diversity, and function. We will use state-of-the-art methodologies including confocal microscopy, rotational rheometry, machine learning-based image analysis, various biochemical methods and high-throughput sequencing (metagenomics/metatranscriptomics). The integration of lab and field data into a biogeochemical model will assess the viral impacts of carbon exports in coastal systems. By converging marine microbial ecology, oceanography, molecular biology, marine chemistry and biophysics, this project advances understanding of viral roles in marine carbon cycling, particularly in understudied coastal environments. It supports the European Green Deal by enhancing resilience to climate extremes and addressing climate-linked biological threats. The project establishes a novel research field in Slovenian science, leveraging a multidisciplinary consortium and international collaborators with leading and emerging experts in the field.

SICRIS

Link to the project