Bacterial and Archaeal Assemblages from Two Size Fractions in Submarine Groundwater Near an Industrial Zone

Xiaogang Chen,Qi Ye,Jinzhou Du,Jing Zhang

doi:10.3390/w11061261

Abstract

Nutrients and organic pollutants transported by submarine groundwater discharge (SGD) play a significant role in controlling water quality, and can lead to the concerned deleterious effects on marine ecosystems. Subterranean estuaries are complicated habitats of diverse microbial communities that mediate different biogeochemical processes. However, there is less information on how microorganisms mediate biogeochemical cycles in the submarine groundwater system. In this study, we investigated the changes in bacterial and archaeal assemblages from two size fractions (0.2–0.45 μm and >0.45 μm) in the submarine groundwater of Qinzhou Bay, China. Phylogenetic analysis showed that Bathyarchaeota was dominant in archaeal communities in the >0.45 μm size fraction, but was seldom in the 0.2–0.45 μm fraction. The co-occurrence of sequences belonging to Bathyarchaeota and Methanosaeta was found in the >0.45 μm size fraction. Since a gene encoding acetate kinase of Bathyarchaeota is involved in acetate production, and acetate is also a necessary growth factor for Methanosaeta, the acetate produced by Bathyarchaeota can provide food or energy sources for Methanosaeta in this very >0.45 μm size fraction. The most abundant bacterial sequences in the >0.45 μm size fraction was closely related to biomineral iron-oxidizing Gallionella spp., whereas the dominant bacterial sequences in the 0.2–0.45 μm fraction were affiliated with Limnohabitans spp., which can utilize dissolved organic matter as an important source of growth substrates. Notably, approximately 10% of the bacterial sequences in both of the two size fractions belonged to Novosphingobium spp., which plays an important role in the degradation of pollutants, especially aromatic compounds. Furthermore, the predictive functional profiling also revealed that the pathways involved in the degradation of aromatic compounds by both bacteria and archaea were identified. The presence of nutrients or pollutants in our study site provides different substrates for the growth of the specific microbial groups; in turn, these microbes may help to deplete pollutants to the ocean through submarine groundwater. We suggest that these specific microbial groups could be potential candidates for effective in situ bioremediation of groundwater ecosystems.

Highlights

Submarine groundwater discharge (SGD) is defined as all the water flow on continental margins from the seabed to the coastal ocean, without regard to their fluid composition or driving force [1].Compared with surface water, submarine groundwater has a different geochemistry, and where these waters mix prior to discharging, they form reactive zones known as the subterranean estuary [2].The composition of SGD differs from that predicted by simple mixing, because biogeochemical reactionsWater 2019, 11, 1261; doi:10.3390/w11061261 www.mdpi.com/journal/waterWater 2019, 11, x FOR PEER REVIEW Compared1261 surface water, submarine groundwater has a different geochemistry, and where these waters mix prior to discharging, they form reactive zones known as the subterranean estuary [2]
Approximately 10% of the bacterial sequences in both of the two size fractions belonged to Novosphingobium spp., which plays an important role in the degradation of pollutants, especially aromatic compounds
We found that three dominant bathyarchaeotal operational taxonomic taxonomic unit unit (OTU) (OTU 563, 516 and 598) were affiliated with our Bathyarchaeota subgroup 6 (Figure 6), showing similar ecological potentials to those of this subgroup 6

Summary

Introduction

Submarine groundwater discharge (SGD) is defined as all the water flow on continental margins from the seabed to the coastal ocean, without regard to their fluid composition or driving force [1].Compared with surface water, submarine groundwater has a different geochemistry, and where these waters mix prior to discharging, they form reactive zones known as the subterranean estuary [2].The composition of SGD differs from that predicted by simple mixing, because biogeochemical reactionsWater 2019, 11, 1261; doi:10.3390/w11061261 www.mdpi.com/journal/waterWater 2019, 11, x FOR PEER REVIEW Compared1261 surface water, submarine groundwater has a different geochemistry, and where these waters mix prior to discharging, they form reactive zones known as the subterranean estuary [2]. Submarine groundwater has a different geochemistry, and where these waters mix prior to discharging, they form reactive zones known as the subterranean estuary [2]. The composition of SGD differs from that predicted by simple mixing, because biogeochemical reactions. 1261 surface water, submarine groundwater has a different geochemistry, and where these waters mix prior to discharging, they form reactive zones known as the subterranean estuary [2]. The composition of SGD differs from that predicted by simple mixing, because biogeochemical in the aquifer modify itsmodify chemistry [3]. SGD fluxes of nutrients, metals, carbon andcarbon organic pollutants reactions in the aquifer its chemistry [3]. Its chemical associated chemical are substances are key considered coastal management [10]

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