Krinos, A. | bioRxiv Science

bioRxiv2025

New niches for larger phytoplankton in a warmer, more resource-limited ocean

Warming and nutrient limitation are major stressors that affect primary production in the ocean, with cascading impacts on the food web. Yet, we lack a mechanistic understanding of how phytoplankton manage multiple stressors and the implications of these responses for phytoplankton biogeography. By combining theory, proteome allocation modeling, and climate projections, we identified two potential competing strategies for multi-stressor growth: (1) nutrient efficient smaller cells, or (2) heat-tolerant larger cells. We found that Prochlorococcus are more vulnerable in warmer, "heat-stressed", tropical regions due to greater heat sensitivity and lower lipid storage capacity to buffer oxidative stress, indicating a potential ecological niche for larger phytoplankton with lower sensitivity to oxidative stress, such as Synechococcus and picoeukaryotes. Our findings advocate for the inclusion of phytoplankton heat-stress responses in global models to more accurately predict their ecological niches as the climate warms.

ecology↗

bioRxiv2024

Exploring the Phaeosphere: characterizing the microbiomes of Phaeocystis antarctica colonies from the coastal Southern Ocean and laboratory culture

Interactions between phytoplankton and bacteria play critical roles in shaping marine ecosystems. However, the intricate relationships within these communities--particularly in extreme and rapidly changing environments like the coastal Southern Ocean--remain poorly understood. Here, we apply targeted methods to directly characterize the microbiomes of individual colonies of Phaeocystis antarctica, a keystone phytoplankton species in the Southern Ocean, for the first time. We show that colony microbiomes are consistent in distinct geographic locations at approximately the same time, but shift significantly after a year of laboratory culture. The bacterial orders Alteromonadales, Oceanospirillales, and Sphingomonadales dominated the microbiomes of all field-collected colonies, whereas Caulobacterales, Cellvibrionales, and Rhodobacterales dominated colony microbiomes after culturing. Notably, the most abundant genera in field-collected colony microbiomes, the psychrophiles Paraglaciecola and Colwellia, were lost in culture. The shift in microbiome structure emphasizes the importance of field-based studies to capture the complexity of microbial interactions, especially for species from polar environments that are difficult to replicate in laboratory conditions. Furthermore, the relative abundances of bacterial taxa comprising the majority of field-collected colony microbiomes--e.g., Paraglaciecola sp. (Alteromonadales) and Nitrincolaceae (Oceanospirillales)--were strongly associated with Phaeocystis abundance in surface waters, highlighting their potential roles in bloom dynamics and carbon cycling. This research provides valuable insights into the ecological significance of prokaryotic interactions with a key phytoplankton species and underscores the necessity of considering these dynamics in the context of climate-driven shifts in marine ecosystems.

microbiology↗