Stephens, B. | bioRxiv Science

bioRxiv2023

Microbial Respiration in Contrasting Ocean Provinces via High-Frequency Optical Assays

Microbial respiration plays a pivotal role in the marine carbon cycle, influencing the fraction of fixed carbon that undergoes remineralization versus export to depth. Despite its importance, methodological constraints have led to an inadequate understanding of this process, especially in low-activity oligotrophic and mesopelagic regions. Here, we quantify respiration rates as low as 0.2 {micro}mol O2 L-1 d-1 in contrasting ocean productivity provinces using optical oxygen sensors to identify size-fractionated respiration trends. At the low productivity North Pacific Ocean Station Papa, surface microbial respiration was relatively stable at 1.2 {micro}mol O2 L-1 d-1. Below the surface there was a decoupling of respiration and bacterial production potentially driven by phytodetritus remineralization. Size-fractionated rates showed cells <5 {micro}m contributed the most to Pacific respiration. At the North Atlantic Porcupine Abyssal Plain, the optode measurement frequency was drastically increased. Surface microbial respiration was higher (1.7 {micro}mol O2 L-1 d-1) and decreased by 3-fold below the euphotic zone. The Atlantic filtered fraction contributions to total respiration shifted with the phytoplankton bloom evolution. The high resolution optode method used in the Atlantic is consistent with coinciding in vivo 2-para-(iodophenyl)-3(nitrophenyl)-5(phenyl) tetrazolium chloride respiratory stain measurements and historical site estimates. We estimate that 58% of gross primary production was respired at the Pacific site and 34% at the Atlantic site, demonstrating that the Atlantic had a higher carbon export potential. This study highlights the dynamic nature of respiration across vertical, temporal, and size-fractionated factors, emphasizing the need for sensitive, high-throughput techniques to better understand ocean ecosystem metabolism.

microbiology↗

bioRxiv2018

Microbial and Metabolic Succession on Common Building Materials Under High Humidity Conditions

Despite considerable efforts to characterize the ecology of bacteria and fungi in the built environment (BE), the metabolic mechanisms underpinning their colonization and successional dynamics remain unclear. Here, we applied bacterial/viral particle counting, qPCR, 16S and ITS rRNA amplicon sequencing, and metabolomics to longitudinally characterize the ecological dynamics of four commonly used building materials maintained at high humidity conditions (~94% RH). We varied the natural inoculum provided to each material by placing them in different occupied spaces, and we wet the surface of half of the samples of each material to simulate a flooding event. As expected, different materials showed different bacterial and viral particle abundance, with wet materials having higher growth rates and lower alpha diversity compared to non-wetted materials. Wetting described the majority of the variance in bacterial, fungal and metabolite structure, and material type only influenced bacterial and metabolic diversity, while location of inoculation was only weakly associated with bacterial and fungal beta diversity. Metabolites indicative of microbial activity were identified, as were those that were native to the surface material. Glucose-phosphate was abundant on all materials (except mold-free gypsum) and was correlated with Enterobacteriaceae, which could indicate a potential bacterial nutrient source. A compound consistent with scopoletin, a plant metabolite with antimicrobial activity, was significantly negatively correlated with Bacillus and positively correlated with Pseudomonas and enriched in medium density fiberboard (MDF) materials. In wet samples, the alkaloids nigragillin and fumigaclavine C, both with antimicrobial properties, were significantly positively correlated with the fungal phylum Ascomycota. Nigragillin, was also negatively correlated with Bacillus and Pseudomonas abundance. Thiabendazole and azoxystrobin (anti-fungal compounds) were highly abundant on mold-resistant gypsum wallboard and likely directly influenced the decreased fungal growth observed on this material. The mold-resistant gypsum material also showed a significant increase in bacterial alpha diversity, and bacterial and viral particle abundance, as well as a decrease in metabolite diversity, likely a result of reduced fungal growth. Penicillium taxa were positively correlated with thiabendazole, which suggested the persistence of resistant strains. Also, specific to the wet samples, Bacillus abundance was positively correlated with the azoxystrobin, suggesting bi-directional competitive adaptation, and positively correlated with metabolites known to interfere with Pseudomonas biofilm formation, which could explain the anti-correlation between these taxa. As expected, high moisture conditions enabled faster growth of inoculating microorganisms, whose composition, chemistry, and competition was shaped by surface material, suggesting that both fungal and bacterial growth need to be considered when determining the impact of dampness in built environments.

microbiology↗