Coastal Bacterioplankton Metabolism Is Stimulated Stronger by Anthropogenic Aerosols than Saharan Dust

Abstract

In oligotrophic regions, such as the Mediterranean Sea, atmospheric deposition has the potential to stimulate heterotrophic prokaryote growth and production in surface waters, especially during the summer stratification period. Previous studies focused on the role of leaching nutrients from mineral particles of Saharan (S) origin, and were restricted to single locations at given times of the year. In this study, we evaluate the effect of atmospheric particles from diverse sources and with a markedly different chemical composition [S dust and anthropogenic (A) aerosols] on marine planktonic communities from three locations of the northwestern Mediterranean with contrasted anthropogenic footprint. Experiments were also carried out at different times of the year, considering diverse initial conditions. We followed the dynamics of the heterotrophic community and a range of biogeochemical and physiological parameters in six experiments. While the effect of aerosols on bacterial abundance was overall low, bacterial heterotrophic production was up to 3.3 and 2.1 times higher in the samples amended with A and S aerosols, respectively, than in the controls. Extracellular enzymatic activities [leu-aminopeptidase (AMA) and β-glucosidase (β-Gl)] were also enhanced with aerosols, especially from A origin. AMA and β-Gl increased up to 7.1 in the samples amended with A aerosols, and up to 1.7 and 2.1 times, respectively, with S dust. The larger stimulation observed with A aerosols might be attributed to their higher content in nitrate. However, the response was variable depending the initial status of the seawater. In addition, we found that both A and S aerosols stimulated bacterial abundance and metabolism significantly more in the absence of competitors and predators.

Dust-Associated Airborne Microbes Affect Primary and Bacterial Production Rates, and Eukaryotes Diversity, in the Northern Red Sea: A Mesocosm Approach

“…We show that AMA and β-Gl activities increased significantly with dust addition, while APA rates decreased significantly ( Figure 3A-E). Synthesis of extracellular enzymes are dependent on nutrient availability (APA dependent on P, AMA and β-Gl dependent on organic carbon) and their activity rates change with the input of nutrients via atmospheric deposition [71,72]. The β-Gl activity is attributed mostly to heterotrophic bacteria [30,73], while AMA activity is attributed to heterotrophic bacteria as well as cyanobacteria, phytoplankton, and zooplankton [30,[73][74][75] and its activities have been shown to increase after aerosol addition in a microcosm study in the Mediterranean Sea [72].…”

“…Synthesis of extracellular enzymes are dependent on nutrient availability (APA dependent on P, AMA and β-Gl dependent on organic carbon) and their activity rates change with the input of nutrients via atmospheric deposition [71,72]. The β-Gl activity is attributed mostly to heterotrophic bacteria [30,73], while AMA activity is attributed to heterotrophic bacteria as well as cyanobacteria, phytoplankton, and zooplankton [30,[73][74][75] and its activities have been shown to increase after aerosol addition in a microcosm study in the Mediterranean Sea [72]. Specifically, β-Gl is utilized in hydrolysis of cellobiose found in polymers, such as cellulose and mucopolysaccharides, and can be related to Chl-a [76,77], whereas AMA is utilized in the decay of particulate matter composed of biotic and abiotic material [74,75].…”

“…Specifically, β-Gl is utilized in hydrolysis of cellobiose found in polymers, such as cellulose and mucopolysaccharides, and can be related to Chl-a [76,77], whereas AMA is utilized in the decay of particulate matter composed of biotic and abiotic material [74,75]. APA, synthesized by phytoplankton [73], has also been shown to vary in response to dust additions to the Mediterranean [71,72] and northern Red Sea [78] seawater during incubation experiments. Changes in enzymatic activity were observed in both the UV-treated dust and live dust treatments as compared with the control, showing that chemical components of atmospheric deposition are enhanced in-situ microbial activities, as previously suggested.…”

Atmospheric Deposition Impact on Bacterial Community Composition in the NW Mediterranean

“…Total suspended particles were sampled at the Institut de Ciències del Mar of Barcelona (41.39° N, 2.20° E) and at the Centre d’Estudis Avançats of Blanes (41.68° N, 2.80° E) on days that Saharan particles arrived to the northeastern (NE) Iberian Peninsula (“SD” aerosols) or during normal meteorological conditions (“AA” aerosols). Total suspended particles were, thereby, collected on quartz fiber filters (Munktell; Falun, Sweden) by means of a CAV-A/mb high volume sampler (30 m 3 h -1 , 24 h; MCV; Barcelona, Spain), following the same protocol as in Marín et al (2017a,b). SD and AA were classified based on advanced event warnings for the NE Iberian Peninsula 1 and the element ratios criteria defined in the literature (Wedepohl, 1995; Migon et al, 2001; Guieu et al, 2010; Nava et al, 2012).…”

“…Marine bacterioplankton have been shown to benefit from both SD and AA (Pulido-Villena et al, 2008; Reche et al, 2009; Ternon et al, 2011; Marín et al, 2017b). However, their effect on the bacterial community composition remains poorly studied, with most of the previous work focusing on the effect of SD and using molecular techniques of low taxonomic resolution based on fluorescence in situ hybridization or denaturing gradient gel electrophoresis (Reche et al, 2009; Lekunberri et al, 2010; Marañón et al, 2010; Laghdass et al, 2012; Pulido-Villena et al, 2014).…”