Shifts in Root-Associated Microbial Communities of Typha Latifolia Growing in Naphthenic Acids and Relationship to Plant Health

Abstract

Naphthenic acids (NAs) are a complex mixture of organic acid compounds released during the extraction of crude oil from oil sands operations. The accumulation of toxic NAs in tailings pond water (TPW) is of significant environmental concern, and phytoremediation using constructed wetlands is one remediation option being assessed. Since root-associated microorganisms are an important factor during phytoremediation of organic compounds, this study investigated the impact of NAs on the microbial communities associated with the macrophyte Typha latifolia (cattail). Denaturing gradient gel electrophoresis revealed that the impact of NAs on microbial communities was niche dependent, with endophytic communities being the most stable and bulk water communities being the least stable. The type of NA used was significant to microbial response, with commercial NAs causing greater adverse changes than TPW NAs. In general, plant beneficial bacteria such as diazotrophs were favoured in cattails grown in TPW NAs, while potentially deleterious bacteria such as denitrifying Dechlorospirillum species increased in commercial NA treatments. These findings suggest that NAs may affect plant health by impacting root-associated microbial communities. A better understanding of these impacts may allow researchers to optimize those microbial communities that support plant health, and thus further optimize wetland treatment systems.

KEY WORDS:

• endophytic bacteria
• macrophytes
• microbial community analysis
• naphthenic acids
• oil sands
• phytoremediation

ACKNOWLEDGMENTS

Financial support was provided by the Natural Sciences and Engineering Research Council of Canada (NSERC) and by the Program of Energy and Research Development (PERD).

Notes

*No significant difference was observed between heterotrophic numbers within a given niche at time 0, and averaged values for each niche (n = 15) are presented for comparison with later populations. Data are presented as log 10 transformed means (n = 3) with standard deviation in parentheses. Means in the same column with the same letter are not significantly different (p < 0.05).

*CFB: Cytophaga-Flexibacter-Bacteroides.

*Naphthenic acid enrichment culture from which bacteria was identified. F: Fluka commercial mixture; O: Oil sands extract.