Evolution of microbial "streamer" growths in an acidic, metal-contaminated stream draining an abandoned underground copper mine.

Catherine Kay,D Johnson,Kris Coupland,Kevin Hallberg,Laura Rocchetti,Owen Rowe

doi:10.3390/life3010189

Catherine Kay, D Johnson + Show 4 more

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https://doi.org/10.3390/life3010189

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Abstract

A nine year study was carried out on the evolution of macroscopic “acid streamer” growths in acidic, metal-rich mine water from the point of construction of a new channel to drain an abandoned underground copper mine. The new channel became rapidly colonized by acidophilic bacteria: two species of autotrophic iron-oxidizers (Acidithiobacillus ferrivorans and “Ferrovum myxofaciens”) and a heterotrophic iron-oxidizer (a novel genus/species with the proposed name “Acidithrix ferrooxidans”). The same bacteria dominated the acid streamer communities for the entire nine year period, with the autotrophic species accounting for ~80% of the micro-organisms in the streamer growths (as determined by terminal restriction enzyme fragment length polymorphism (T-RFLP) analysis). Biodiversity of the acid streamers became somewhat greater in time, and included species of heterotrophic acidophiles that reduce ferric iron (Acidiphilium, Acidobacterium, Acidocella and gammaproteobacterium WJ2) and other autotrophic iron-oxidizers (Acidithiobacillus ferrooxidans and Leptospirillum ferrooxidans). The diversity of archaea in the acid streamers was far more limited; relatively few clones were obtained, all of which were very distantly related to known species of euryarchaeotes. Some differences were apparent between the acid streamer community and planktonic-phase bacteria. This study has provided unique insights into the evolution of an extremophilic microbial community, and identified several novel species of acidophilic prokaryotes.

Highlights

Acidophilic microorganisms are defined as those that grow optimally, or exclusively, in low pH environments, and have been sub-divided into moderate and extremeacidophiles
The Frasassi cave complex in Italy provides an interesting contrast to pyrite-rich mines in that the main energy source for the acidophiles that form snotites is reduced sulfur rather than ferrous iron, and the dominant prokaryotes are sulfur-oxidizers (Acidithiobacillus thiooxidans, with smaller numbers of Sulfobacillus and a bacterium related to Acidimicrobium [5])
Heterotrophic bacteria were detected more regularly by terminal restriction enzyme fragment length polymorphism (T-restriction enzyme fragment length polymorphism (RFLP)) analysis six months after acid mine drainage (AMD) first flowed through the Dyffryn Adda, though non iron-oxidizing heterotrophic acidophiles were always relatively minor, and often more transient, members of the streamer communities

Summary

Introduction

Acidophilic microorganisms are defined as those that grow optimally, or exclusively, in low pH environments, and have been sub-divided into moderate (pH optima 3–5) and extreme (pH optima < 3)acidophiles. Individual cells of acidophilic microorganisms aggregate and form gelatinous macroscopic growths that have been referred to as “acid streamers” (filamentous growths in flowing waters), “acid mats” (thick and often dense growths), and “pipes” / “snotites” (pendulous growths attached to mine roofs or other subterranean features [1]). These have been found in subterranean and surface environments, frequently in and around abandoned mine sites [2]. Little is known about how these communities establish and evolve with time

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