Bacterial-viral interactions in the sea surface microlayer of a black carbon-dominated tropical coastal ecosystem (Halong Bay, Vietnam)

Abstract

Increasing human activity has raised concerns about the impact of deposition of anthropogenic combustion aerosols (i.e., black carbon; BC) on marine processes. The sea surface microlayer (SML) is a key gate for the introduction of atmospheric BC into the ocean; however, relatively little is known of the effects of BC on bacteria-virus interactions, which can strongly influence microbially mediated processes. To study the impact of BC on bacteria-virus interactions, field investigations involving collection from the SML and underlying water were carried out in Halong Bay (Vietnam). Most inorganic nutrient concentrations, as well as dissolved organic carbon, were modestly but significantly higher (p = 0.02-0.05) in the SML than in underlying water. The concentrations of particulate organic carbon (though not chlorophyll a) and of total particulate carbon, which was composed largely of particulate BC (mean = 1.7 ± 6.4 mmol L -1 ), were highly enriched in the SML, and showed high variability among stations. On average, microbial abundances (both bacteria and viruses) and bacterial production were 2-and 5fold higher, respectively, in the SML than in underlying water. Significantly lower bacterial production (p < 0.01) was observed in the particulate fraction (>3 µm) compared to the bulk sample, but our data overall suggest that bacterial production in the SML was stimulated by particulate BC. Higher bacterial production in the SML than in underlying water supported high viral lytic infection rates (from 5.3 to 30.1%) which predominated over percent lysogeny (from undetected to 1.4%). The sorption of dissolved organic carbon by black carbon, accompanied by the high lytic infection rate in the black carbon-enriched SML, may modify microbially mediated processes and shift the net ecosystem metabolism (ratio of production and respiration) to net heterotrophy and CO 2 production in this critical layer between ocean and atmosphere.

Discovery of High Abundances of Aster-Like Nanoparticles in Pelagic Environments: Characterization and Dynamics

“… (A) Distribution of aster-like nanoparticles (ALNs) and bacteria abundances in 16 selected stations of a tropical coastal ecosystem (Ha Long Bay-Vietnam), and (B) analyses of correlations (Spearman's product-moment correlation coefficient) between ALNs and environmental parameters which compile all sampling points. All details on Ha Long Bay (Vietnam) environment are available from Pradeep Ram et al (2018). Level of significance: * p < 0.001.…”

“…This property prompted us to explore the environmental parameters potentially affecting ALN dynamics at the spatial scale. This was achieved on 16 selected geographical stations from Ha long bay estuary in Vietnam, a highly spatially contrasted environment previously characterized by Pradeep Ram et al (2018). This spatial survey indicated significant coupling between ALN and prokaryote abundances (Figure 10).…”

“…Detection of ALNs was also conducted on surface microlayer samples of 16 selected geographical stations (namely HL1 to HL16) from the Ha Long Bay (Vietnam). Details on these samples and their environment were provided in a previous work (Pradeep Ram et al, 2018). ALNs were quantified on electronic microscopy grids prepared as mentioned below.…”

Biogeochemical Impacts of a Black Carbon Wet Deposition Event in Halong Bay, Vietnam

“…Dilution did not have any significant bearing on bacterial counts. This methodology has been previously validated and adopted for reporting bacterial and viral counts in Halong Bay (Pradeep Ram et al, 2018). The mixture was incubated for 5 min, heated for 10 min at 80 • C in the dark, and cooled for 5 min prior to analysis.…”

“…Considering the large amounts of BC continuously entering the ocean, and especially via wet deposition, one may expect this material to impact pelagic systems (Weinbauer et al, 2017). In the atmosphere, BC is associated with other aerosols, the input of BC to the marine environment may lead to an enrichment in BCassociated elements, such as organic carbon (Willey et al, 2000;Raymond, 2005), nutrients (Mahowald et al, 2008;Kanakidou et al, 2012;Wang et al, 2015), trace metals (Paytan et al, 2009;Ito, 2013), and even pesticides (Kunz et al, 2005), potentially altering the structure and activity of phytoplankton (Paytan et al, 2009;Guo et al, 2012) and bacterial (Cattaneo et al, 2010;Mari et al, 2014;Pradeep Ram et al, 2018) communities. In addition, it has been shown that the BC introduced into marine surface waters sorbs dissolved organic matter (DOM), nutrients and small particles, and stimulate aggregation processes (Mari et al, 2014(Mari et al, , 2017a.…”