2 Habitats
Historically, the first well-documented isolate of alkaliphilic bacterium, Bacillus
alcalophilus, is dated by 1934 [5], and short history of alkaliphiles before 1968 had
been surveyed by Horikoshi [6]. Yet, there was an earlier but less documented isolate
dated by 1889: Urobacillus pasteurii ! Bacillus pasteurii and now Sporosarcina
pasteurii [4]. All of the early alkaliphiles were aerobic, and it took decades before the
first alkaliphilic anaerobes, facultative anaerobic Amphibacillus xylanus [7], and
obligate anaerobic Methanosalsum zhilinae (former Methanohalophilus zhilinae)
[8] were isolated. Since then, the growing interest in the unusual, for that time,
group of microorganisms has led to the isolation and identification of a large number
of new species and genera of alkaliphiles. The continuing interest of microbiologists
in this group of extremophiles can be illustrated by a long list of aerobic and anaerobic
alkaliphiles isolated merely from soda lakes around the world, with a total number of
nearly a 150 species [9].
How to find a place where alkaliphiles live? The notion that “Alkaliphiles should
be looked for in alkaline locations” as we will see it further below may not be
evident. This statement is correct, but only in part. The geochemical pathways led to
creation of natural alkaline environments which are known and briefly considered
below. Most prominent example includes soda lakes which are widely distributed
around tropical, subtropical, and intracontinental cryoarid zones of Earth. In such
lakes, alkalinity is created by chemical weathering of igneous or metamorphic
volcanic carbonatite-containing rocks by CO 2 -bearing waters (runoff and groundwater). Various dissolved carbonate species are released into water making it
alkaline. The common feature of all soda lakes in hydrologically closed basins
is a progressive evaporative concentration of inorganic salts, where sodium carbonates are prevailing [10]. Depending on local climatic features, soda lakes mineral
saturation can be both low and high. It is important to emphasize that the composition of the brine will be substantially different (depending on the particulate
waterbody) compared to the evaporation of seawater where sodium chloride dominates and the ratio chloride/sulfate will near constant up to the beginning of the solid
precipitation. The highest pH value achieved in the soda lake is determined by the
pH of the sodium carbonate solution and usually does not exceed 11. Numerous
examples of soda lakes can be found in the East African Rift Valley (Ethiopia,
Kenya, Tanzania), in the eastern Turkey (Lake Van, the largest alkaline lake on
Earth), alkaline lakes of the Great Basin in the western USA, and numerous Asian
alkaline shallow lakes of Mongolia, China, India, and the southern Siberia in Russia.
In addition to their biotechnological potential as sources of new extremophilic
microorganisms, soda lakes have attracted the attention of paleomicrobiologists as
possible counterparts of Precambrian water bodies, whose microorganisms probably
gave the entire modern variety of prokaryotes. The idea of a high biodiversity of the
microbial population of soda lakes, put forward by the Russian microbiologist
George Zavarzin in the 1990s [11], was confirmed in the following years, when
the number of publications on the isolation and description of new alkaliphiles began
to increase rapidly. The microbial communities inhabiting soda lakes are mostly
56
V. V. Kevbrin
Historically, the first well-documented isolate of alkaliphilic bacterium, Bacillus
alcalophilus, is dated by 1934 [5], and short history of alkaliphiles before 1968 had
been surveyed by Horikoshi [6]. Yet, there was an earlier but less documented isolate
dated by 1889: Urobacillus pasteurii ! Bacillus pasteurii and now Sporosarcina
pasteurii [4]. All of the early alkaliphiles were aerobic, and it took decades before the
first alkaliphilic anaerobes, facultative anaerobic Amphibacillus xylanus [7], and
obligate anaerobic Methanosalsum zhilinae (former Methanohalophilus zhilinae)
[8] were isolated. Since then, the growing interest in the unusual, for that time,
group of microorganisms has led to the isolation and identification of a large number
of new species and genera of alkaliphiles. The continuing interest of microbiologists
in this group of extremophiles can be illustrated by a long list of aerobic and anaerobic
alkaliphiles isolated merely from soda lakes around the world, with a total number of
nearly a 150 species [9].
How to find a place where alkaliphiles live? The notion that “Alkaliphiles should
be looked for in alkaline locations” as we will see it further below may not be
evident. This statement is correct, but only in part. The geochemical pathways led to
creation of natural alkaline environments which are known and briefly considered
below. Most prominent example includes soda lakes which are widely distributed
around tropical, subtropical, and intracontinental cryoarid zones of Earth. In such
lakes, alkalinity is created by chemical weathering of igneous or metamorphic
volcanic carbonatite-containing rocks by CO 2 -bearing waters (runoff and groundwater). Various dissolved carbonate species are released into water making it
alkaline. The common feature of all soda lakes in hydrologically closed basins
is a progressive evaporative concentration of inorganic salts, where sodium carbonates are prevailing [10]. Depending on local climatic features, soda lakes mineral
saturation can be both low and high. It is important to emphasize that the composition of the brine will be substantially different (depending on the particulate
waterbody) compared to the evaporation of seawater where sodium chloride dominates and the ratio chloride/sulfate will near constant up to the beginning of the solid
precipitation. The highest pH value achieved in the soda lake is determined by the
pH of the sodium carbonate solution and usually does not exceed 11. Numerous
examples of soda lakes can be found in the East African Rift Valley (Ethiopia,
Kenya, Tanzania), in the eastern Turkey (Lake Van, the largest alkaline lake on
Earth), alkaline lakes of the Great Basin in the western USA, and numerous Asian
alkaline shallow lakes of Mongolia, China, India, and the southern Siberia in Russia.
In addition to their biotechnological potential as sources of new extremophilic
microorganisms, soda lakes have attracted the attention of paleomicrobiologists as
possible counterparts of Precambrian water bodies, whose microorganisms probably
gave the entire modern variety of prokaryotes. The idea of a high biodiversity of the
microbial population of soda lakes, put forward by the Russian microbiologist
George Zavarzin in the 1990s [11], was confirmed in the following years, when
the number of publications on the isolation and description of new alkaliphiles began
to increase rapidly. The microbial communities inhabiting soda lakes are mostly
56
V. V. Kevbrin