High dissolved extracellular enzymatic activity in the deep central Atlantic Ocean

Abstract

The distribution of prokaryotic abundance (PA), prokaryotic heterotrophic production (PHP), and suspended particulate organic material (POM), as well as total and dissolved (operationally defined as passing through 0.2 µm pore size filters) potential extracellular enzymatic activities (EEA; α-and β-glucosidase [AGase and BGase], leucine aminopeptidase [LAPase], and alkaline phosphatase [APase]) were determined in the meso-and bathypelagic waters of the (sub)tropical Atlantic along an eastern zonal transatlantic transect and a western N-S transect. Significant differences between both transects were found for POM concentration but not for PA, PHP (except in the subsurface and oxygen minimum layer), and dissolved and total EEA. PHP decreased by 3 orders of magnitude from the lower euphotic zone to bathypelagic waters, while PA and cell-specific PHP decreased only by 1 and 2 orders of magnitude, respectively. The proportion of the dissolved to the total EEA was high in the dark ocean for all the enzymes, ranging from 54 to 100, 56 to 100, 65 to 100 and 57 to 97% for AGase, BGase, LAPase and APase, respectively. The kinetic parameters (V max and K m ) of both the dissolved and total fractions of LAPase and APase were very similar throughout the water column, suggesting a similar origin for both dissolved and particulate EEA. Significant correlations of both dissolved and total EEA were found with prokaryotic metabolism and the POM pool. Based on the previous notion that the fraction of dissolved EEA is higher in particle-attached than in free-living microbes, our results suggest that microbial activity in the dark ocean occurs mainly on colloidal and particulate material. This is in agreement with recent genomic evidence. However, these colloidal and particulate materials are prone to disruption during the sampling process. Hence, more selective sampling techniques are needed to specifically collect these deep-water aggregates that probably represent hotspots of microbial activity in the deep ocean.

Phosphate monoesterase and diesterase activities in the North and South Pacific Ocean

“…The proportion was lower at SCM than at 10 m, which is apparently inconsistent with a previous report that the importance of dissolved extracellular enzymatic activities, including that of alkaline phosphatase to total activity, increased towards deeper water (Baltar et al, 2010). However, this report resulted from a survey throughout the whole water column, including the aphotic zone, and the samples for the photic zone were collected only from the depth of 100 m. Therefore, the results from the present study suggest that the relationship between the proportion of MEA in the dissolved fraction and depth is different between the photic and aphotic zones.…”

Role of macroscopic particles in deep-sea oxygen consumption

“…The possibility suggested here, that most microbial metabolism is associated with macroscopic particles, is supported by several recent observations in the deep sea. First, freely dissolved enzymatic activity is proportionally higher in the deep sea than the surface ocean, a strategy of adaptive advantage only seen where substrates are in close proximity to the microbes, such as in detrital particles (32). Second, viral abundances do not decrease with depth as rapidly as expected from the decrease of prokaryotic biomass with depth (33).…”

Cell-free extracellular enzymatic activity is linked to seasonal temperature changes: a case study in the Baltic Sea

“…Until recently, most EEA in the marine environment was believed to be associated with cells (Hoppe, 1983;Hoppe et al, 2002) leading to the perception that only cellassociated EEs were of ecological significance (Chrost and Rai, 1993;Rego et al, 1985;Someville and Billen, 1983). However, other reports suggested a major contribution of dissolved EEA to the total oceanic EEA pool (Baltar et al, 2010;Baltar et al, 2013Baltar et al, , 2010Karner and Rassoulzadegan, 1995;Keith and Arnosti, 2001;Obayashi and Suzuki, 2008a). This high proportion of cell-free EEA is important because it can decouple hydrolysis rates of organic material from microbial dynamics.…”

“…winter). This hypothesis is based on the previous evidences of higher lifetimes of EEA in cold compared to warm waters (Baltar et al, 2010), suggesting that an overall low metabolic rate of microbes would favour higher percentages of dissolved EEA because the degradation of the enzymes (i.e. microbial heterotrophic activity) is reduced under lower temperatures.…”

“…This high proportion of cell-free EEA is important because it can decouple hydrolysis rates of organic material from microbial dynamics. Thus, a high proportion of dissolved EEA could indicate a greater importance of the history of the water mass than of the actual processes occurring at the time of sampling (Arnosti, 2011;Baltar et al, 2010;Baltar et al, 2013;Karner and Rassoulzadegan, 1995).…”