Microbial Abundance and Enzyme Activity Patterns: Response to Changing Environmental Characteristics along a Transect in Kongsfjorden (Svalbard Islands)

Abstract

Svalbard archipelago is experiencing the effects of climate changes (i.e., glaciers' thickness reduction and glacier front retreat), but how ice melting affects water biogeochemistry is still unknown. Microbial communities often act as environmental sentinels, modulating their distribution and activity in response to environmental variability. To assess microbial response to climate warming, within the ARctic: present Climatic change and pAst extreme events (ARCA) project, a survey was carried out along a transect in Konsfjorden from off-shore stations towards the Kronebreen glacier. Total bacterial abundance and the fraction of actively respiring cells (labelled by cyanotetrazolium chloride, CTC), cultivable heterotrophic bacterial abundance, and extracellular enzymatic activities (leucine aminopeptidase (LAP), beta-glucosidase (GLU), and alkaline phosphatase (AP)) were measured. In addition, water temperature, salinity, dissolved oxygen, turbidity, total suspended matter (TSM), particulate and chromophoric dissolved organic matter (CDOM), chlorophyll-a (Chl-a), and inorganic compounds were determined, in order to evaluate whether variations in microbial abundance and metabolism were related with changes in environmental variables. Colder waters at surface (3.5–5 m) depths and increased turbidity, TSM, and inorganic compounds found at some hydrological stations close to the glacier were signals of ice melting. CDOM absorption slope values (275–295 nm) varied from 0.0077 to 0.0109 nm−1, and total bacterial cell count and cultivable heterotrophic bacterial abundance were in the order of 106 cells/mL and 103 colony forming units/mL, respectively. Enzymatic rates <1.78, 1.25, and 0.25 nmol/l/h were recorded for AP, LAP, and GLU, respectively. Inorganic compounds, TSM, and turbidity correlated inversely with temperature; AP was significantly related with CDOM absorption spectra and heterotrophic bacteria (r = 0.59, 0.71, P < 0.05); and LAP with Chl-a, Particulate Organic Carbon (POC) and Particulate Organic Nitrogen (PON) (0.97, 0.780, 0.734, P < 0.01), suggesting that fresh material from ice melting stimulated the metabolism of the cultivable fraction.

Ice Melt-Induced Variations of Structural and Functional Traits of the Aquatic Microbial Community along an Arctic River (Pasvik River, Norway)

“…However, if during Ice-melt (−) high values of GLU and AP activities (Figure 3a) suggest a relation to photosynthetic production, during the Ice-melt (+) period, higher LAP activities indicate the occurrence of fresh labile compounds, probably deriving from ice melting related to a summer temperature increase and river inputs. An increase in enzymatic activity rates in relation to the release of organic matter from ice melting was also observed along a transect within Kongsfjorden (Svalbard) in May 2016 [36], confirming that organic carbon sources stimulate the microbial community to produce enzymes to decompose the available organic polymers. Moreover, as observed in coastal to off-shore gradients [37,38], increased runoff not only affects the organic matter pool but also changes the dynamics of coastal bacterial communities with a shift toward a higher influence of riverine bacteria, with implications on the metabolic profiles and organic matter degradation capability of such communities.…”

A Snapshot of the Taxonomic Composition and Metabolic Activity of the Microbial Community in an Arctic Harbour (Ny-Ålesund, Kongsfjorden, Svalbard)

“…Culturable heterotrophic bacterial count in seawater samples was obtained through the "spread plate method", through inoculation of 0.1 mL of sample on plates of Marine agar 2216 (Conda Pronadisa, Madrid, Spain), a medium specific for the cultivation of heterotrophic bacteria [51]. Marine agar was chosen in this study as the culture medium to better compare the heterotrophic bacterial counts with those determined in other Arctic environments [25,38].…”

“…L-leucine-4methylcoumarinylamide hydrochloride, 4-methylumbelliferyl B-D-glucopyranoside, and 4-methylumbelliferyl phosphate (Merck Life Sciences, Milan, Italy) were the substrates specific for LAP, ß-GLU, and AP. Seawater samples were dispensed into three test tubes (10 mL each) plus one autoclaved sample (Blank tube), which were added increasing volumes (10 to 320 nmol L −1 ) of each substrate separately, according to the procedure already described in Caruso et al [25]. The sediment was diluted 1:10 in sterile physiological solution, and the supernatant obtained after re-suspension was divided into triplicate sub-volumes that were incubated with each substrate in concentrations of 20 to 160 µM (stock solution 5 mM).…”

“…In marine sediments chronically exposed to oil contamination, microbial community composition and metabolism were reported to vary in relation with both temperature and chemical diversity [24]; furthermore, bacterial richness and catabolic diversification increased under chronic pollution at low temperature [24]. Moreover, climate warming, which is an ongoing issue in the Arctic region, as shown by glacier retreat, sea ice melting, and increases in suspended sediment inputs into coastal marine environments, might influence the dynamics and the trophic level interactions within the microbial community, with consequent implications on large-scale ecological processes [25,26].…”

“…Exposed to strong Atlantic and glacial runoff influence [27], it is a widely studied marine ecosystem [28]; here, many physical and biological features are being addressed by several countries which have established their research stations at Ny-Ålesund [29]. To date, an important number of studies have explored the structure and function of the bacterial community across the entire Kongsfjorden marine system, both at a pelagic and sedimentary level [25,[30][31][32][33][34][35][36][37][38][39][40]. Data on microbial distribution and its role in this Arctic area are mostly fragmentary, due to the lack of comprehensive studies, as evidenced by recent literature reviews [29,40].…”