Dynamics of Sediment Microbial Functional Capacity and Community Interaction Networks in an Urbanized Coastal Estuary.

Tianjiao Dai,Qinglin Mu,Bei Huang,Daliang Ning,Yan Zhang,Donghui Wen,Yushi Tang,Zhiguo Su

doi:10.3389/fmicb.2018.02731

Abstract

Coastal estuaries and bays are exposed to both natural and anthropogenic environmental changes, inflicting intensive stress on the microbial communities inhabiting these areas. However, it remains unclear how microbial community diversity and their eco-functions are affected by anthropogenic disturbances rather than natural environmental changes. Here, we explored sediment microbial functional genes dynamics and community interaction networks in Hangzhou Bay (HZB), one of the most severely polluted bays on China’s eastern coast. The results indicated key microbial functional gene categories, including N, P, S, and aromatic compound metabolism, and stress response, displayed significant spatial dynamics along environmental gradients. Sensitive feedbacks of key functional gene categories to N and P pollutants demonstrated potential impacts of human-induced seawater pollutants to microbial functional capacity. Seawater ammonia and dissolved inorganic nitrogen (DIN) was identified as primary drivers in selecting adaptive populations and varying community composition. Network analysis revealed distinct modules that were stimulated in inner or outer bay. Importantly, the network keystone species, which played a fundamental role in community interactions, were strongly affected by N-pollutants. Our results provide a systematic understanding of the microbial compositional and functional dynamics in an urbanized coastal estuary, and highlighted the impact of human activities on these communities.

Highlights

Microbes provide the dominant diversity and biomass in coastal ecosystems, and play a vital role in biogeochemical cycles, climate regulation, and pollutant degradation (Azam and Malfatti, 2007; Lunau et al, 2013; Poi et al, 2013)
The decrease of dissolved ammonia, inorganic nitrogen (DIN), total phosphorus (TP), and Chemical oxygen demand (COD) in the seawater implied the input of land-sourced pollutants
Due to a strong hydrodynamic flow, dissolved oxygen (DO) in most sites met the threshold for the Class I standard (DO > 6 mg/L), except S2 and Z5, which may be due to the influence of oxygen consuming compounds and increased water depth, respectively

Summary

Introduction

Microbes provide the dominant diversity and biomass in coastal ecosystems, and play a vital role in biogeochemical cycles, climate regulation, and pollutant degradation (Azam and Malfatti, 2007; Lunau et al, 2013; Poi et al, 2013). Numerous studies have suggested that coastal microbial community structures are greatly driven by salinity (Fortunato et al, 2011; Campbell and Kirchman, 2013), depth (Hewson et al, 2007; Boer et al, 2009), nutrients (Wang et al, 2015), dissolved oxygen (DO) (Fortunato et al, 2013; Jeffries et al, 2016), and temperature (Fortunato et al, 2013; Meziti et al, 2016) These factors, which are spatiotemporally dynamic, are crucial to the growth of individual taxa as well as the formation of a given community composition and biogeography pattern. Identifying microbial dynamics in response to pollutant input at the species or community level is thought to be useful in evaluating possible impacts of anthropogenic disturbance (Aguirre et al, 2017; Richa et al, 2017)

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