Research Projects

Research Organisation Partners

• National Institute of Biology
•  Institute Jožef Štefan
• University of Ljubljana, Biotechnical Faculty

Abstract

Phytoplankton contributes significantly to marine primary productivity (MPP) and plays a key role in carbon sequestration via the biological carbonpump (BCP). Diatoms, a major phytoplankton group, account for ~25% of MPP and are critical to BCP due to their silicified cell walls, which act asmineral ballast. Viral infections are a key factor influencing BCP and carbon export efficiency (CEE). Viruses exhibit dual roles in marineecosystems: they may enhance carbon export via the "viral shuttle" mechanism by promoting the formation of sinking aggregates or reduce it viathe "viral shunt," which redirects organic carbon to dissolved organic matter (DOM) for microbial respiration. The interplay between thesemechanisms depends on environmental and biological factors, including phytoplankton physiology, microbial community composition, and watercolumn 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 TheirMicrobial 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 infectionsalter DOM quality, supporting distinct microbial communities and processes, with effects varying by virus type. While microbial processes inphytoplankton aggregates have been studied, their link to viral infections remains unexplored. This project aims to bridge this gap by integratinglaboratory experiments, field studies, and advanced modelling to elucidate how viral infections modify the physical, chemical, and microbiologicalproperties of aggregates, thereby affecting marine carbon cycling. The research will focus on diatoms and diatom viruses from our culturecollection, with the potential inclusion of haptophyte systems. Fieldwork will target the Northern Adriatic Sea, a productive, shallow, and well-mixedcoastal 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, influencingmicrobial processing in the water column and CEE. To test these hypotheses, we will analyse differences between aggregates from healthy andinfected phytoplankton populations (lab cultures and environmental samples), their physicochemical properties, and their support for microbialgrowth, 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 laband field data into a biogeochemical model will assess the viral impacts of carbon exports in coastal systems. By converging marine microbialecology, oceanography, molecular biology, marine chemistry and biophysics, this project advances understanding of viral roles in marine carboncycling, particularly in understudied coastal environments. It supports the European Green Deal by enhancing resilience to climate extremes andaddressing climate-linked biological threats. The project establishes a novel research field in Slovenian science, leveraging a multidisciplinaryconsortium and international collaborators with leading and emerging experts in the field.

Researchers

• 39120 - Timotej Turk Dermastia
• 35384 - Denis Kutnjak
• 34499 - Katja Klun
• 29618 - Tinkara Tinta
• 11360 - Patricija Mozetič
• 59081 - Simone Spinelli
• 54508 - Živa Muhič
• 31481 - Martin Vodopivec
• 57003 - Petra Slavinec
• 51831 - Neža Orel
• 27827 - Jon Gutierrez Aguirre
• 38081 - Anja Pecman
• 24407 - Iztok Dogša
• 57307 - Marko Volk
• 53622 - Mojca Blaznik
• 13005 - David Stopar
• 29539 – Vid Podpečan
• 53799 – Martin Marzidovšek

The phases of the project and their realization

We will start with observing infection effects on aggregation capabilities of model diatom-virus systems, moving to wild-type novel isolate systems, which will be characterized. In this phase, physical properties of aggregates will be studied. In the second phase we will study microbial propreties of aggregates, colonization and microbiome structure. Lastly, we will collect natural aggregates and particles and relate the aquired knowledge from the laboratory to observation in the natural environment of the Northern Adriatic.