The diversity of PAH-degrading bacteria in a deep-sea water column above the Southwest Indian Ridge.

Jun Yuan

doi:10.3389/fmicb.2015.00853

Abstract

The bacteria involved in organic pollutant degradation in pelagic deep-sea environments are largely unknown. In this report, the diversity of polycyclic aromatic hydrocarbon (PAH)-degrading bacteria was analyzed in deep-sea water on the Southwest Indian Ridge (SWIR). After enrichment with a PAH mixture (phenanthrene, anthracene, fluoranthene, and pyrene), nine bacterial consortia were obtained from depths of 3946–4746 m. While the consortia degraded all four PAHs when supplied in a mixture, when PAHs were tested individually, only phenanthrene supported growth. Thus, degradation of the PAH mixture reflected a cometabolism of anthracene, fluoranthene, and pyrene with phenanthrene. Further, both culture-dependent and independent methods revealed many new bacteria involved in PAH degradation. Specifically, the alpha and gamma subclasses of Proteobacteria were confirmed as the major groups within the communities. Additionally, Actinobacteria, the CFB group and Firmicutes were detected. Denaturing Gradient Gel Electrophoresis (DGGE) analysis showed that bacteria closely affiliated with Alcanivorax, Novosphingobium, and Rhodovulum occurred most frequently in different PAH-degrading consortia. By using general heterotrophic media, 51 bacteria were isolated from the consortia and of these 34 grew with the PAH mixture as a sole carbon source. Of these, isolates most closely related to Alterierythrobacter, Citricella, Erythrobacter, Idiomarina, Lutibacterium, Maricaulis, Marinobacter, Martelella, Pseudidiomarina, Rhodobacter, Roseovarius, Salipiger, Sphingopyxis, and Stappia were found to be PAH degraders. To the best of our knowledge, this is the first time these bacteria have been identified in this context. In summary, this report revealed significant diversity among the PAH-degrading bacteria in the deep-sea water column. These bacteria may play a role in PAH removal in deep-sea environments.

Highlights

Polycyclic aromatic hydrocarbons (PAHs) are a group of cytotoxic, mutagenic and carcinogenic compounds with two or more fused aromatic rings
PAH Degradation by Deep Water Layers After the initial 2 months enrichment with a PAH mixture of phenanthrene, anthracene, fluoranthene, and pyrene as the sole carbon and energy sources, PAH degradation occurred in all treatment conditions of nine layers of water samples acquired from 3946 to 4746 m
The initial enrichment cultures were transferred to fresh NH medium with PAHs as the sole carbon source

Summary

Introduction

Polycyclic aromatic hydrocarbons (PAHs) are a group of cytotoxic, mutagenic and carcinogenic compounds with two or more fused aromatic rings. They can be found in deep-sea sediments, such as those found 2.7 m beneath the bottom surface at a water depth of 3,962 m on the Middle Atlantic Ridge. This locations has a total PAH concentration ( PAHs) of 260 ∼440 ng/g dw (dry weight). Even higher PAH concentrations were detected in the hydrothermal vent area of the South Mid-Atlantic Ridge (Huang et al, 2014). The origin and fate of PAHs in this extreme environment are not well understood

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