Comparative metagenomics study reveals pollution induced changes of microbial genes in mangrove sediments

Yingdong Li,Hongbin Liu,Hongmei Jing,Liping Zheng,Yue Zhang

doi:10.1038/s41598-019-42260-4

Abstract

Mangrove forests are widespread along the subtropical and tropical coasts. They provide a habitat for a wide variety of plants, animals and microorganisms, and act as a buffer zone between the ocean and land. Along with other coastal environments, mangrove ecosystems are under increasing pressure from human activities, such as excessive input of nutrients and toxic pollutants. Despite efforts to understand the diversity of microbes in mangrove sediments, their metabolic capability in pristine and contaminated mangrove sediments remains largely unknown. By using metagenomic approach, we investigated the metabolic capacity of microorganisms in contaminated (CMS) and pristine (PMS) mangrove sediments at subtropical and tropical coastal sites. When comparing the CMS with PMS, we found that the former had a reduced diazotroph abundance and nitrogen fixing capability, but an enhanced metabolism that is related to the generation of microbial greenhouse gases via increased methanogenesis and sulfate reduction. In addition, a high concentration of heavy metals (mainly Zn, Cd, and Pb) and abundance of metal/antibiotic resistance encoding genes were found in CMS. Together, these data provide evidence that contamination in mangrove sediment can markedly change microbial community and metabolism; however, no significant differences in gene distribution were found between the subtropical and tropical mangrove sediments. In summary, contamination in mangrove sediments might weaken the microbial metabolisms that enable the mangrove ecosystems to act as a buffer zone for terrestrial nutrients deposition, and induce bioremediation processes accompanied with an increase in greenhouse gas emission.

Highlights

Mangrove ecosystems are widely distributed in the transition between land and sea, along the estuaries and coastlines in subtropical and tropical regions
With regards to the amounts of metals in the sediment, the concentration of Zn was higher in the Contaminated mangrove sediment (CMS) than in the PMS in both subtropical (i.e., with 3577.11 mg/kg in contaminated mangrove sediment of Haikou (HKC) and 2687.74 mg/kg in pristine mangrove sediment of Haikou (HKP)) and tropical (i.e., with 371.14 mg/kg in contaminated mangrove sediment of Sanya (SYC) and 205.53 mg/kg in pristine mangrove sediment of Sanya (SYP)) samples
The methane flux across the mangrove sediment-atmosphere interface was higher in the CSM (0.286~0.578 mg·m−2 h−1) than in the PMS (−0.143~−0.017 mg·m−2 h−1), and a higher methane flux was measured in the subtropical mangrove sediment than in the tropical sites (Table S1)

Summary

Introduction

Mangrove ecosystems are widely distributed in the transition between land and sea, along the estuaries and coastlines in subtropical and tropical regions. Mangroves act as a natural sewage treatment plant, exhibiting a robust ecosystem restoration capacity[4,5], the ever increasing levels of contaminants are overloading mangrove sediments, and this influences their restoration and nutrient cycling capacity by affecting the sediment-inhabiting microorganisms[6,7,8,9]. Metals are retained in mangrove sediments rather than moving to adjacent environments, but this markedly influences the autochthonic microbial community[15] Both metals and metalloids have been shown to contribute to the abundance and distribution of ammonia-oxidizing archaea and beta-proteobacteria, both of which are crucial to www.nature.com/scientificreports/. We explored the community structure and metabolism capacity of the microorganisms in the heavily polluted and relatively pristine mangrove sediments in both tropical Sanya and subtropical Haikou using a metagenomic approach

Methods

Results

Discussion

Conclusion