Distribution of Acidophilic Microorganisms in Natural and Man-made Acidic Environments.

Sabrina Hedrich,Axel Schippers

doi:10.21775/cimb.040.025

Abstract

Acidophilic microorganisms can thrive in both natural and man-made environments. Natural acidic environments comprise hydrothermal sites on land or in the deep sea, cave systems, acid sulfate soils and acidic fens, as well as naturally exposed ore deposits (gossans). Man-made acidic environments are mostly mine sites including mine waste dumps and tailings, acid mine drainage and biomining operations. The biogeochemical cycles of sulfur and iron, rather than those of carbon and nitrogen, assume centre stage in these environments. Ferrous iron and reduced sulfur compounds originating from geothermal activity or mineral weathering provide energy sources for acidophilic, chemolithotrophic iron- and sulfur-oxidizing bacteria and archaea (including species that are autotrophic, heterotrophic or mixotrophic) and, in contrast to most other types of environments, these are often numerically dominant in acidic sites. Anaerobic growth of acidophiles can occur via the reduction of ferric iron, elemental sulfur or sulfate. While the activities of acidophiles can be harmful to the environment, as in the case of acid mine drainage, they can also be used for the extraction and recovery of metals, as in the case of biomining. Considering the important roles of acidophiles in biogeochemical cycles, pollution and biotechnology, there is a strong need to understanding of their physiology, biochemistry and ecology.

Highlights

Environments inhabited by acidophiles can be of natural origin where acidic conditions have existed for many years, such as volcanic or geothermal areas, or environments where acidity has arisen due to human activities, such as mining of metals and coal
Owing to the limited oxygen ingress reported for Mynydd Parys, activities of iron-oxidizing microorganisms seemed to be low, but ferric iron reduction catalysed by autotrophic and heterotrophic bacteria, as well as due to reaction with pyrite and other residual sulfide minerals, led to ferrous iron being the dominant form in the subterranean lake ( Johnson, 2012)
Even so the mat was dominated by iron-oxidizing bacteria, high concentrations of ferrous iron could be detected, which is explained by the presence of heterotrophic iron-reducing microorganisms (Acidiphilium spp., Acidobacteriaceae) whose growth was postulated to be supported by organic carbon released by the algae

Summary

Introduction

Environments inhabited by acidophiles can be of natural origin where acidic conditions have existed for many years, such as volcanic or geothermal areas, or environments where acidity has arisen due to human activities, such as mining of metals and coal. The subterranean waters were dominated by iron-oxidizing Acidithiobacillus spp., and even so the exact species was not determined at this time, the dominance of At. ferrivorans is most likely due to the low temperatures and subsequent studies (Coupland and Johnson, 2004).

Results

Conclusion