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Abstract. Oceanic bacterial communities process a major fraction of marine organiccarbon. A substantial portion of this carbon transformation occurs in themesopelagic zone, and a further fraction fuels bacteria in the bathypelagiczone. However, the capabilities and limitations of the diverse microbialcommunities at these depths to degrade high-molecular-weight (HMW) organicmatter are not well constrained. Here, we compared the responses of distinctmicrobial communities from North Atlantic epipelagic (0–200 m), mesopelagic(200–1000 m), and bathypelagic (1000–4000 m) waters at two open-oceanstations to the same input of diatom-derived HMW particulate and dissolvedorganic matter. Microbial community composition and functional responses tothe input of HMW organic matter – as measured by polysaccharide hydrolase,glucosidase, and peptidase activities – were very similar between thestations, which were separated by 1370 km but showed distinct patterns withdepth. Changes in microbial community composition coincided with changes inenzymatic activities: as bacterial community composition changed in responseto the addition of HMW organic matter, the rate and spectrum of enzymaticactivities increased. In epipelagic mesocosms, the spectrum of peptidaseactivities became especially broad and glucosidase activities were veryhigh, a pattern not seen at other depths, which, in contrast, were dominatedby leucine aminopeptidase and had much lower peptidase and glucosidase ratesin general. The spectrum of polysaccharide hydrolase activities was enhancedparticularly in epipelagic and mesopelagic mesocosms, with fewerenhancements in rates or spectrum in bathypelagic waters. The timing andmagnitude of these distinct functional responses to the same HMW organicmatter varied with depth. Our results highlight the importance of residencetimes at specific depths in determining the nature and quantity of organicmatter reaching the deep sea.
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Particles act as ‘specialty centers’ with expanded enzymatic function throughout the water column in the western North Atlantic
Heterotrophic bacteria initiate the degradation of high molecular weight organic matter by producing an array of extracellular enzymes to hydrolyze complex organic matter into sizes that can be taken up into the cell. These bacterial communities differ spatially and temporally in composition, and potentially also in their enzymatic complements. Previous research has shown that particle-associated bacteria can be considerably more active than bacteria in the surrounding bulk water, but most prior studies of particle-associated bacteria have been focused on the upper ocean - there are few measurements of enzymatic activities of particle-associated bacteria in the mesopelagic and bathypelagic ocean, although the bacterial communities in the deep are dependent upon degradation of particulate organic matter to fuel their metabolism. We used a broad suite of substrates to compare the glucosidase, peptidase, and polysaccharide hydrolase activities of particle-associated and unfiltered seawater microbial communities in epipelagic, mesopelagic, and bathypelagic waters across 11 stations in the western North Atlantic. We concurrently determined bacterial community composition of unfiltered seawater and of samples collected via gravity filtration (>3 μm). Overall, particle-associated bacterial communities showed a broader spectrum of enzyme activities compared with unfiltered seawater communities. These differences in enzymatic activities were greater at offshore than at coastal locations, and increased with increasing depth in the ocean. The greater differences in enzymatic function measured on particles with depth coincided with increasing differences in particle-associated community composition, suggesting that particles act as ‘specialty centers’ that are essential for degradation of organic matter even at bathypelagic depths.
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- PAR ID:
- 10376541
- Date Published:
- Journal Name:
- Frontiers in Microbiology
- Volume:
- 13
- ISSN:
- 1664-302X
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.3389/fmicb.2022.882333
