Spatial patterns of biphasic ectoenzymatic kinetics related to biogeochemical properties in the Mediterranean Sea

Abstract. Prokaryotic ectoenzymatic activity, abundance and heterotrophic production were determined in the Mediterranean Sea, within the epipelagic and the upper part of the mesopelagic layers. The Michaelis-Menten kinetics were assessed, using a range of low (0.025 to 1 µM) and high (0.025 to 50 µM) concentrations of fluorogenic substrates. Thus, Km and Vm parameters were determined for both low and high affinity systems for alkaline phosphatase (AP), aminopeptidase (LAP) and β-glucosidase (βGLU). Based on the constant derived from the high AP affinity system, in-situ hydrolysis rates of N-protein contributed of 48 % ± 30 % for the heterotrophic prokaryotic nitrogen demand within epipelagic waters and of 180 % ± 154 % within deeper layers. LAP hydrolysis rate was higher than bacterial N demand only within the deeper layer, and only based on the high affinity system. Although ectoenzymatic hydrolysis contribution to heterotrophic prokaryotic need was high in terms of N, but low in terms of C. Based on a 10 % bacterial growth efficiency, the cumulative hydrolysis rates of C-proteins and C-polysaccharides contributed to a small part of the heterotrophic prokaryotic carbon demand, on average 2.5 % ± 1.3 % in the epipelagic layers. This study notably points out the biases in current and past interpretation of the relative activities differences among the 3 tested enzymes, in regard to the choice of added concentrations of fluorogenic substrates. In particular, enzymatic ratios LAP/βGLU, as well as some trends with depth, were different considering activities resulting from the high or the low affinity system.

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Spatial patterns of ectoenzymatic kinetics in relation to biogeochemical properties in the Mediterranean Sea and the concentration of the fluorogenic substrate used

Biogeosciences ◽

10.5194/bg-18-2301-2021 ◽

2021 ◽

Vol 18 (7) ◽

pp. 2301-2323

Author(s):

France Van Wambeke ◽

Elvira Pulido ◽

Philippe Catala ◽

Julie Dinasquet ◽

Kahina Djaoudi ◽

...

Keyword(s):

Mediterranean Sea ◽

Substrate Concentration ◽

Hydrolysis Rate ◽

Bacterial Growth Efficiency ◽

Fluorogenic Substrate ◽

Fluorogenic Substrates ◽

High Affinity ◽

Carbon Demand ◽

Intermediate Waters ◽

The Mediterranean

Abstract. Ectoenzymatic activity, prokaryotic heterotrophic abundances and production were determined in the Mediterranean Sea. Sampling was carried out in the sub-surface, the deep chlorophyll maximum layer (DCM), the core of the Levantine intermediate waters and in the deeper part of the mesopelagic layers. Michaelis–Menten kinetics were assessed using a large range of concentrations of fluorogenic substrates (0.025 to 50 µM). As a consequence, Km (Michaelis–Menten half-saturation constant) and Vm (maximum hydrolysis velocity) parameters were determined for both low- and high-affinity enzymes for alkaline phosphatase, aminopeptidase (LAP) and β-glucosidase (βGLU). Based on the constant derived from the high-LAP-affinity enzyme (0.025–1 µM substrate concentration range), in situ hydrolysis of N proteins contributed 48 % ± 30 % to the heterotrophic bacterial nitrogen demand within the epipelagic layers and 180 % ± 154 % in the Levantine intermediate waters and the upper part of the mesopelagic layers. The LAP hydrolysis rate was higher than bacterial N demand only within the deeper layer and only when considering the high-affinity enzyme. Based on a 10 % bacterial growth efficiency, the cumulative hydrolysis rates of C proteins and C polysaccharides contributed on average 2.5 % ± 1.3 % to the heterotrophic bacterial carbon demand in the epipelagic layers sampled (sub-surface and DCM). This study clearly reveals potential biases in current and past interpretations of the kinetic parameters for the three enzymes tested based on the fluorogenic-substrate concentration used. In particular, the LAP / βGLU enzymatic ratios and some of the depth-related trends differed between the use of high and low concentrations of fluorogenic substrates.

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Temporal Variation of Bacterial Respiration and Growth Efficiency in Tropical Coastal Waters

Applied and Environmental Microbiology ◽

10.1128/aem.01227-09 ◽

2009 ◽

Vol 75 (24) ◽

pp. 7594-7601 ◽

Cited By ~ 30

Author(s):

Choon Weng Lee ◽

Chui Wei Bong ◽

Yii Siang Hii

Keyword(s):

Temporal Variation ◽

Bacterial Growth ◽

Coastal Waters ◽

Bacterial Production ◽

Growth Efficiency ◽

Bacterial Growth Efficiency ◽

Bacterial Respiration ◽

Substrate Quality ◽

Carbon Demand ◽

Net Heterotrophy

ABSTRACT We investigated the temporal variation of bacterial production, respiration, and growth efficiency in the tropical coastal waters of Peninsular Malaysia. We selected five stations including two estuaries and three coastal water stations. The temperature was relatively stable (averaging around 29.5°C), whereas salinity was more variable in the estuaries. We also measured dissolved organic carbon and nitrogen (DOC and DON, respectively) concentrations. DOC generally ranged from 100 to 900 μM, whereas DON ranged from 0 to 32 μM. Bacterial respiration ranged from 0.5 to 3.2 μM O2 h−1, whereas bacterial production ranged from 0.05 to 0.51 μM C h−1. Bacterial growth efficiency was calculated as bacterial production/(bacterial production + respiration), and ranged from 0.02 to 0.40. Multiple correlation analyses revealed that bacterial production was dependent upon primary production (r2 = 0.169, df = 31, and P < 0.02) whereas bacterial respiration was dependent upon both substrate quality (i.e., DOC/DON ratio) (r2 = 0.137, df = 32, and P = 0.03) and temperature (r2 = 0.113, df = 36, and P = 0.04). Substrate quality was the most important factor (r2 = 0.119, df = 33, and P = 0.04) for the regulation of bacterial growth efficiency. Using bacterial growth efficiency values, the average bacterial carbon demand calculated was from 5.30 to 11.28 μM C h−1. When the bacterial carbon demand was compared with primary productivity, we found that net heterotrophy was established at only two stations. The ratio of bacterial carbon demand to net primary production correlated significantly with bacterial growth efficiency (r2 = 0.341, df = 35, and P < 0.001). From nonlinear regression analysis, we found that net heterotrophy was established when bacterial growth efficiency was <0.08. Our study showed the extent of net heterotrophy in these waters and illustrated the importance of heterotrophic microbial processes in coastal aquatic food webs.

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Dissolved and particulate primary production along a longitudinal gradient in the Mediterranean Sea

Biogeosciences ◽

10.5194/bg-8-815-2011 ◽

2011 ◽

Vol 8 (3) ◽

pp. 815-825 ◽

Cited By ~ 67

Author(s):

D. C. López-Sandoval ◽

A. Fernández ◽

E. Marañón

Keyword(s):

Primary Production ◽

Mediterranean Sea ◽

Small Degree ◽

Euphotic Layer ◽

Relative Contribution ◽

Carbon Demand ◽

Extracellular Release ◽

Photosynthetic Production ◽

Longitudinal Pattern ◽

The Mediterranean

Abstract. We have determined the photosynthetic production of dissolved (DOCp) and particulate organic carbon (POCp) along a longitudinal transect in the Mediterranean Sea during the summer stratification period. The euphotic layer-integrated rates of DOCp and POCp ranged between approximately 50–130 and 95–210 mgC m−2 d−1, respectively, and showed an east to west increasing trend. For the whole transect, the relative contribution of DOCp to total, euphotic layer-integrated primary production (percentage of extracellular release, PER) averaged ~37% and did not show any clear longitudinal pattern. In spite of the relatively high PER values, the measured DOCp rates were much lower than the estimated bacterial carbon demand, suggesting a small degree of coupling between phytoplankton exudation and bacterial metabolism. Our results, when compared with previous measurements obtained with the same methods in several ecosystems of contrasting productivity, support the view that the relative importance of DOCp increases under strong nutrient limitation.

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Viral effects on bacterial respiration, production and growth efficiency: Consistent trends in the Southern Ocean and the Mediterranean Sea

Deep Sea Research Part II Topical Studies in Oceanography ◽

10.1016/j.dsr2.2007.12.004 ◽

2008 ◽

Vol 55 (5-7) ◽

pp. 790-800 ◽

Cited By ~ 38

Author(s):

Osana Bonilla-Findji ◽

Andrea Malits ◽

Dominique Lefèvre ◽

Emma Rochelle-Newall ◽

Rodolphe Lemée ◽

...

Keyword(s):

Southern Ocean ◽

Mediterranean Sea ◽

Growth Efficiency ◽

Bacterial Respiration ◽

The Mediterranean

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Low bacterial growth efficiency in the oligotrophic eastern Mediterranean Sea: a modelling analysis

Journal of Plankton Research ◽

10.1093/plankt/25.9.1011 ◽

2003 ◽

Vol 25 (9) ◽

pp. 1011-1019 ◽

Cited By ~ 9

Author(s):

T. R. Anderson

Keyword(s):

Mediterranean Sea ◽

Bacterial Growth ◽

Eastern Mediterranean ◽

Growth Efficiency ◽

Bacterial Growth Efficiency ◽

Eastern Mediterranean Sea ◽

Modelling Analysis

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Effect of CO<sub>2</sub> enrichment on bacterial production and respiration and on bacterial carbon metabolism in Arctic waters

Biogeosciences Discussions ◽

10.5194/bgd-9-15213-2012 ◽

2012 ◽

Vol 9 (10) ◽

pp. 15213-15235 ◽

Cited By ~ 4

Author(s):

C. Motegi ◽

T. Tanaka ◽

J. Piontek ◽

C. P. D. Brussaard ◽

J. P. Gattuso ◽

...

Keyword(s):

Carbon Metabolism ◽

Bacterial Production ◽

Growth Efficiency ◽

Mesocosm Experiment ◽

Bacterial Growth Efficiency ◽

Temporary Increase ◽

Bacterial Respiration ◽

Clear Trend ◽

Carbon Demand ◽

The Impact

Abstract. The impact of rising carbon dioxide (pCO2) on bacterial production (BP), bacterial respiration (BR) and bacterial carbon metabolism was investigated during the mesocosm experiment in Kongsfjord (Svalbard) in 2010. The mesocosm experiment lasted 30 days and nine mesocosms with pCO2 levels ranging from ca. 180 to 1400 μatm were used. Generally, BP gradually decreased in all mesocosms in an initial phase, showed a large (3.6-fold in average) but temporary increase on day 10, and increased slightly afterwards. BP increased with increasing pCO2 at the beginning of the experiment (day 5). This trend became inversed and BP decreased with increasing pCO2 on day 14 (after nutrient addition). Interestingly, increasing pCO2 enhanced the leucine and thymidine ratio at the end of experiment, suggesting that pCO2 may alter the growth balance of bacteria. In contrast to BP, no clear trend and effect of changes of pCO2 was observed for BR, bacterial carbon demand and bacterial growth efficiency. Our results suggest that (1) the response to elevated pCO2 had a strong temporal variation, potentially linked to the nutrient status, and (2) pCO2 had an influence on biomass accumulation (i.e. BP) rather than on the conversion of dissolved organic matter into CO2 (i.e. BR).

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Dissolved and particulate primary production along a longitudinal gradient in the Mediterranean Sea

Biogeosciences Discussions ◽

10.5194/bgd-7-8591-2010 ◽

2010 ◽

Vol 7 (6) ◽

pp. 8591-8617 ◽

Cited By ~ 5

Author(s):

D. C. López-Sandoval ◽

A. Fernández ◽

E. Marañón

Keyword(s):

Primary Production ◽

Mediterranean Sea ◽

Small Degree ◽

Euphotic Layer ◽

Relative Contribution ◽

Carbon Demand ◽

Extracellular Release ◽

Photosynthetic Production ◽

Longitudinal Pattern ◽

The Mediterranean

Abstract. We have determined the photosynthetic production of dissolved (DOCp) and particulate organic carbon (POCp) along a longitudinal transect in the Mediterranean Sea during the summer stratification period. The euphotic layer-integrated rates of DOCp and POCp ranged between approximately 50–130 and 95–210 mgC m−2 d−1, respectively, and showed an east to west increasing trend. For the whole transect, the relative contribution of DOCp to total, euphotic layer-integrated primary production (percentage of extracellular release, PER) averaged ~37% and did not show any clear longitudinal pattern. In spite of the relatively high PER values, the measured DOCp rates were much lower than the estimated bacterial carbon demand, suggesting a small degree of coupling between phytoplankton exudation and bacterial metbolism. Our results, when compared with previous measurements obtained with the same methods in several ecosystems of contrasting productivity, support the view that the relative importance of DOCp increases under strong nutrient limitation.

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