Particles act as ‘specialty centers’ with expanded enzymatic function throughout the water column in the western North Atlantic

Abstract

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.

Distinct bacterial succession and functional response to alginate in the South, Equatorial, and North Pacific Ocean

“…These enzymes specifically cleave phenylalanine and arginine moieties, but their significance within the context of alginate in marine environments is unknown. Findings that chymotrypsin and trypsin may be preferentially produced by PA taxa (Lloyd et al, 2022)-particularly at locations where this present study was conducted (Balmonte et al, 2021)-suggest a role in the degradation of particulate matter. The stimulation of chondroitin and laminarin hydrolysis, particularly in the North Pacific, indicates that the addition of one polysaccharide type induces the hydrolysis of others by stimulating microbial generalists, including those associated with particles.…”

A focus on different types of organic matter particles and their significance in the open ocean carbon cycle

“…Regardless it is by now evident that attached prokaryotic cells are more productive (sometimes by a few orders of magnitude) than their free livings counterparts (Turley and Mackie 1994;Simon et al 2002;Grossart et al 2003a;Baumas et al 2021;Church et al 2021). This is also confirmed by measurements of enzymatic activities on sinking particles (Smith et al 1992;Grossart et al 2003a;b;Tamburini et al 2006;Kellogg and Deming 2014;D'Ambrosio et al 2014;Prairie et al 2015;Balmonte et al 2020;Zhao et al 2020;Lloyd et al 2022). Since carbon remineralization rates are a parameter of paramount importance regarding BCP, it would be worthwhile to establish common protocols for its determination and calculation (Bach et al 2019).…”