The Microbiology of Extremely Acidic Environments
D. Barrie Johnson1 and
Angeles Aguilera2
1College of Natural Sciences, Bangor University, Deiniol Road, Bangor, LL57 2UW, UK
e-mail: d.b.johnson@bangor.ac.uk
Tel: +44 1248 382358
2Centro
de Astrobiología (INTA-CSIC), Carretera de Ajalvir Km4, 28850 Madrid,Spain.
e-mail: aguileraba@cab.inta-csic.esTel: +34 520 6461
Contents
Abstract & Highlights
1.
Nature
and diversity of extremely acidic environments
2.
Diversity
of acidophiles, and adaptation to living in low pH environments
3. Diversity of eukaryotic acidophiles
4.
Physiological and phylogenetic diversity of prokaryotic acidophiles
5.
Ecological and biotechnological
aspects
Abstract
Extremely acidic environments, defined having a pH of
<3, are found in locations as diverse as the Arctic and the Tropics. While
these can be natural phenomena, human activity, most notoriously mining of
metals and coals, is often responsible for the severe acidification of localized
environments. The indigenous microflora in extremely acidic environments
includes species of prokaryotes and eukaryotes, many of which are obligately
acidophilic. Acidophiles are widely distributed throughout the “tree of life”
and include species of Bacteria, Archaea, and Eukarya that are often only very distantly related
to each other. Various mechanisms are used by acidophiles to adapt to the
challenges they face, which include contending with elevated concentrations of
transition metals and metalloids, and severely limited bioavailability of
macronutrients such as phosphate. Inorganic energy sources (reduced iron and
sulfur) are highly abundant in many extremely acidic environments. Chemolithotrophic
acidophiles are the basis of food webs in subterranean and also contribute to
net primary production in deep submarine geothermal vents. However, where solar
energy is available phototrophic acidophiles, predominantly species of
acidophilic eukaryotic microalgae, proliferate and assume the dominant role of primary
producers. Acidophilic microorganisms interact with each other in various ways,
including via redox transformations of iron and sulfur, generating
electron donors and acceptors for prokaryotic metabolisms, and via provision
of organic compounds (supporting heterotrophic species) or inorganic carbon
(supporting autotrophs). Acidophiles have long been used to extract metals from
ores (biomining) and biotechnologies are emerging that harness their abilities
to remediate polluted waters and recover metals.
Highlights (major points covered)
·
The
characteristics and origins of extremely acidic environments
·
How
acidophiles adapt to acid stress and elevated concentrations of metals
·
An
overview of the physiological and phylogenetic diversities of prokaryotic and
eukaryotic microorganisms
·
The
microbial ecology of extremely acidic environments
·
Application
of acidophiles in established and emerging biotechnologies
