ALKALITHERMOPHILES: A DOUBLE CHALLENGE FROM EXTREME ENVIRONMENTS
V. V. KEVBRIN1, C. S. ROMANEK2 AND J.
WIEGEL3
1lnstitute of Microbiology RAS, Prospect 60-letija Octiabria,
7/2, 117312 Moscow, Russia;
2Savannah River Ecology Laboratory, Aiken, SC and Department
of Geology, University of Georgia, Athens, GA 30602;
3Department of Microbiology, University of Georgia, Athens,
GA 30602-2605, USA
1. Introduction
The study of extremophilic microorganisms, in short extremophiles, has
increased drastically over the last few years. An illustration for this
increased interest is the establishment of the new International Society
for Extremophiles and the recently introduced journal Extremophiles. Microorganisms
are named extremophiles when they are well adapted to and grow optimally
at environmental and physicochemical parameters unsuitable for the typical
and widely studied mesophilic microorganisms, such as Escherichia
coli, Bacillus subtilis and Neurospora crassa, to name a
few.
Despite the accelerated description of novel species, most of the described
extremophiles are characterized only by one distinctive 'extreme'. In
this chapter, we discuss a subgroup of 'multi-extremophiles' coined the
alkalithermophiles (also referred to as thermoalkaliphiles). They are
of interest to the scope of this book for two reasons: 1) ancestral alkalithermophiles
could have been one of the earliest forms of life as some geochemical
models and geological evidence suggest that the ocean of Early Earth was
alkaline in nature and capable of supporting primitive alkaliphilic microorganisms,
and 2) alkalithermophiles can be regarded as one type of model organism
for the study of possible extraterrestrial life. We believe alkalithermophilic
microorganisms are one of the possible types of organisms that could have
evolved on Mars, if life ever arose there (see below). Based on reasoning
as discussed elsewhere (Wiegel and Adams, 1998), the authors believe that
life probably originated not in hyperthermobiotic environments but on
mineral surfaces in moderate thermobiotic (e.g., 60-85°C range), relatively
shallow pools at the edges of the early Earth's oceans. The drastic changes
in physico-chemical parameters over space and time in such an environment
would have provided the necessary dynamic conditions for frequent association
and dissociation of prebiotic and biotic structures, with changing selection
pressures leading to superior surviving combinations (Shock et al., 1998;
Baross, 1998; Miller and Lazcano, 1998). These assumed selection conditions
proposedly lead to a 'bush-like origin' of life as suggested by Kandler
(1998) and thus is different from the frequently assumed quasi monophylygenetic
progenote. As such, some form of alkalithermophile can be proposed as
a logical descendant of hypothetical early life forms.
SREL Reprint #2845
Kevbrin, V. V. 2004. Alkalithermophiles: A double challenge from extreme environments. p. 1-16. In Origins: Genesis, Evolution and Diversity of Life, edited by J. Seckbach. Kluwer Academic Publishers, Dordrecht, NL.
