Biology subjects

Mundy, C. J.

Publications and source records attributed to Mundy, C. J..

3 recordsLinked to original sources

bioRxiv2024

Nitrogen cycling during an Arctic bloom: from chemolithotrophy to nitrogen assimilation

In the Arctic, phytoplankton blooms are recurring phenomena occurring during the spring-summer seasons and influenced by the strong polar seasonality. Besides, bloom dynamics is affected by nutrient availability, especially nitrogen, which is the main limiting nutrient in the Arctic. This study aimed to investigate the changes in an Arctic microbial community during a phytoplankton bloom with a special focus on the nitrogen cycle. Using metagenomic and metatranscriptomic samples from the Dease Strait (Canada) from March to July (2014), we reconstructed 176 metagenome-assembled genomes. Bacteria dominated the microbial community, although archaea reached up to 25% of genomic abundance in early spring, when Nitrososphaeria archaea actively expressed genes associated with ammonia oxidation to nitrite (amt, amoA, nirK). The resulting nitrite was presumably further oxidized to nitrate by a Nitrospinota bacterium that highly expressed a nitrite oxidoreductase gene (nxr). Since May, the constant increase in chlorophyll a indicated the occurrence of a phytoplankton bloom, promoting the successive proliferation of different groups of chemoorganotrophic bacteria (Bacteroidetes, Alphaproteobacteria and Gammaproteobacteria). These bacterial taxa showed different strategies to obtain nitrogen, whether it be from organic or inorganic sources, according to the expression patterns of genes encoding transporters for nitrogen compounds. In contrast, during summer, the chemolithotrophic organisms thriving during winter, reduced their relative abundance and the expression of their catabolic genes. Based on the functional analysis of our data, we see a transition from a community where nitrogen-based chemolitotrophy plays a relevant role, to a chemoorganotrophic community based on the carbohydrates released during the phytoplankton bloom, where different groups specialize in different nitrogen sources.

microbiology↗

bioRxiv2023

Specialized Bacteroidetes dominate the Arctic Ocean during marine spring blooms

A metagenomic time series from Arctic seawater was obtained from the Canadian region of Dease Strait, to analyse the changes in bacterioplankton caused by the phytoplankton bloom that recurrently occurs in summer. This dataset documents the growth of bacterial clades specialised in the metabolism of plysaccharides, such as Bacteroidetes, along with the phytoplackton. These specialised taxa quickly displaced the microbial clades that dominate nutrient-poor waters during early spring, such as Archaea, Alpha- and Gammaproteobacteria. At the functional level, phyla Bacteroidetes, Planctomycetes and Verrucomicrobia showed higher contents of polysaccharide-degradation functions. Glycoside hydrolases revealed that the Bacteroidetes community shifted towards species with higher polysaccharide-degrading capabilities, targeting algal polysaccharides in summer. Regarding transporters, Bacteroidetes dominated SusC-TonB transporters and had an exclusive family of glycoside-binding proteins (SusD). These proteins were used to identify polysaccharide-utilisation loci that clustered transporters and polysaccharide-active enzymes, showing a higher level of specialisation towards polysaccharide use. Put together, all these genomic features point to the genetic adaptations that promote the dominance of Bacteroidetes during phytoplankton blooms.

microbiology↗

bioRxiv2022

Bacterioplankton taxa compete for iron along the early spring-summer transition in the Arctic Ocean

Microbial assemblages under sea ice of Dease Strait, Canadian Arctic, were sequenced for metagenomes and metatranscriptomes of the small size fraction (0.2 to 3 {micro}m). The community from early March was typical for this season, with Alpha- and Gammaproteobacteria as the dominant taxa, followed by Thaumarchaeota and Bacteroidetes. Towards summer, Bacteroidetes and particularly the genus Polaribacter, became increasingly dominant, followed by the Gammaproteobacteria. Analysis of genes responsible for microbial acquisition of iron showed an abundance of ABC transporters for divalent cations and ferrous iron. The most abundant transporters, however, were the outer membrane TonB dependent transporters of iron-siderophore complexes. The abundance of iron acquisition genes suggested this element was essential for the microbial assemblage. Interestingly, Gammaproteobacteria were responsible for most of the siderophore synthesis genes. On the contrary, Bacteroidetes did not synthesize siderophores but accounted for most of the transporters, suggesting a role as cheaters in the competition for siderophores as public goods. Likely, this cheating ability of the Bacteroidetes contributed to their dominance in summer.

ecology↗