Marilena Heitger | Amano Lab | Hokkaido University

Major contribution of particle‐associated microbes to deep‐sea organic carbon degradation

Thu, 01 Jan 2026 00:00:00 +0000

The biological carbon pump mediates the export of particulate organic carbon from the euphotic zone to the deep ocean, where it provides the base of the food web. Although deep‐sea microbial metabolism is considered to be largely associated with macroscopic particles, such as marine snow, the specific contribution of particle‐associated microorganisms to the utilization of bulk organic matter has rarely been directly quantified. We used in situ pumps to collect particles larger than 3 μ m from mesopelagic and bathypelagic waters along a latitudinal transect in the North Atlantic. Prokaryotic abundance, respiration, heterotrophic biomass production, and community composition were determined and compared to the bulk prokaryotic community collected by Niskin bottles. Although particle‐associated prokaryotes represented less than 1% of bulk prokaryotic abundance, they contributed on average 28% to bulk prokaryotic respiration and 12% to biomass production. The organic carbon turnover time of particles mediated by prokaryotes was 0.5–1.5 months, while it was up to 3 yr for the total organic carbon fraction. Thus, particles represent hotspots of organic carbon remineralization in the mesopelagic and bathypelagic ocean. Furthermore, metagenomic analyses revealed clear differences in taxonomy and diversity between the free‐living (0.2–0.8 μ m) and particle‐associated (> 3 μ m) prokaryotic communities. Our results emphasize the significant role of particle‐associated prokaryotes in driving organic matter utilization in the dark ocean.

Autofluorescence Is a Common Trait in Different Oceanic Fungi

Sun, 29 Aug 2021 00:00:00 +0000

Natural autofluorescence is a widespread phenomenon observed in different types of tissues and organisms. Depending on the origin of the autofluorescence, its intensity can provide insights on the physiological state of an organism. Fungal autofluorescence has been reported in terrestrial and human-derived fungal samples. Yet, despite the recently reported ubiquitous presence and importance of marine fungi in the ocean, the autofluorescence of pelagic fungi has never been examined. Here, we investigated the existence and intensity of autofluorescence in five different pelagic fungal isolates. Preliminary experiments of fungal autofluorescence at different growth stages and nutrient conditions were conducted, reflecting contrasting physiological states of the fungi. In addition, we analysed the effect of natural autofluorescence on co-staining with DAPI. We found that all the marine pelagic fungi that were studied exhibited autofluorescence. The intensity of fungal autofluorescence changed depending on the species and the excitation wavelength used. Furthermore, fungal autofluorescence varied depending on the growth stage and on the concentration of available nutrients. Collectively, our results indicate that marine fungi can be auto-fluorescent, although its intensity depends on the species and growth condition. Hence, oceanic fungal autofluorescence should be considered in future studies when fungal samples are stained with fluorescent probes (i.e., fluorescence in situ hybridization) since this could lead to misinterpretation of results.