Structuring of marine prokaryotic gene expression by temperature and dissolved organic matter

• Temperature and dissolved organic matter (DOM) are important drivers of marine microbial activity, but their effects, alone or in combination, on the physiological responses of sub-arctic prokaryotic assemblages remain poorly understood. In a one-month mesocosm experiment initiated in early March in the northern Baltic Sea, we thus exposed a coastal microbial community to temperature and nutrient regimes representative of winter and early summer (i.e., 1°C and 10°C, with and without DOM additions) in a 2x2 factorial design. Prokaryotic abundance and heterotrophic production increased until around day 17 in the 10°C mesocosms. Yet, mid through the experiment (days 10 and 17, when samples for metatranscriptomics analyses were analyzed), estimates of growth rates were highest for the 10°C plus DOM treatment (TN; ~2.5 day-1), comparable for the 1°C plus DOM (N) and the 10°C treatments (T; ~1.0 day-1), and low for the control (C; 0.2 day-1). PCA analysis showed that samples for prokaryotic transcription in the 1°C plus DOM and the 10°C treatments clustered in different directions from the control, and the combined 10°C plus DOM treatment triggered even further changes. Taxonomic analysis of the transcripts uncovered broad treatment specific responses. This included a dominance of Nitrosopumilus (Archaea) in the 1°C mesocosms (with and without DOM), an increase in the relative expression of Alphaproteobacteria (both Rhodobacterales and SAR11) in the 10°C mesocosms without DOM addition, and an increase in Oceanospirillales in the 10°C plus DOM treatment. Burkholderiales (Betaproteobacteria) maintained a high relative expression (up to 25%) in all mesocosms. A PERMANOVA on the total of 182,618 transcribed genes revealed statistically significant effects of both temperature and DOM, and also a significant interaction effect between the two factors. EdgeR analysis identified significant differential transcription for up to 10% of the genes in each of the tested contrasts. Prominent features among the significant genes included Nitrosopumilus genes for ammonium uptake and ammonia oxidation in the 1°C mesocosms (C, N), membrane transporters for small organic acids in the N-treatment, genes for N and P assimilation along with molecular chaperones in the T-treatment, and dominance of Oceanospirillales genes for energy and growth metabolism in the TN treatment. These metatranscriptomics responses were associated with changes in ecologically important characteristics of the prokaryotic communities, such as growth rates and growth efficiency, providing clues to how successional changes in community composition and metabolism are induced by environmental conditions linked with seasonality.

Ämnesord

NATURVETENSKAP  -- Biologi -- Ekologi (hsv//swe)

NATURAL SCIENCES  -- Biological Sciences -- Ecology (hsv//eng)

Nyckelord

Ecology

Ekologi

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