alkaliphiles from which many alkaliphiles have been isolated [1, 2]. Similarly, soda
deserts, soda pans, solonchak soils, salt pans, oceans, etc. are known supporting this
remarkable group of organisms [3–7]. Alkaliphiles have also been isolated from the
steady-state alkaline environments that exist in the body of other organisms such
as insect guts [8–10]. Serpentinization, low-temperature weathering of silicate
containing calcium and magnesium minerals like olivine (MgFeSiO 4 ) and pyroxene
(MgCaFeSiO 3 ), forms a highly alkaline Ca
2+ -rich environment [11]. Alkaliphiles
such as Alkaliphilus hydrothermalis [12] and Serpentinicella alkaliphila [13] have
been isolated from such serpentine environments. Anthropogenic activities such as
indigo dye production, potato peeling using KOH, cement/concrete production,
electroplating, leather tanning, paper and board manufacture, mining, and herbicide
manufacturing create alkaline environments [14–18]. Regardless of the difference in
the genesis, chemistry, and stability, all known alkaline environments are inhabited
by alkaliphiles, and this is discussed in detail by Kevbrin [19].
High pH environments are not easy to live in without special adaptations. For
instance, maintaining structural integrity, bioenergetics, and intracellular pH homeostasis are barriers for non-alkaliphiles to survive and thrive in this extreme environment. On the other hand, alkaliphiles evolved adaptive solutions to circumvent
these barriers and thrive lavishly in environments with pH values of up to over
13 [16]. However, adaptation always comes with price. Indeed, there is no single
organism that flourishes in a pH range of 1–13. At least in this case, the rule of nature
seems clear, when an organism evolves adaptations to thrive in specific pH condition
(acidic, neutral, or alkaline), its fitness to live in a habitat of different pH condition
is often compromised. Thus, the adaptation range of alkaliphiles determines their
ability to survive in neutral conditions. As the optimum pH for growth varies among
alkaliphiles, the ability to grow in neutral zone is also different. The growth of
obligate alkaliphiles is compromised around neutral condition. On the other hand,
facultative alkaliphiles can grow at neutral pH but not as lavishly as neutralophiles
[20–22]. Similarly, at or above pH 10, the growth yield of facultative alkaliphiles is
often lower than that of obligate alkaliphiles. This may indicate that alkaliphiles
evolved to colonize high pH environments at a cost of losing growth potency around
neutrality.
This chapter presents the grand challenges of life in high pH environments and
tries to summarize the adaptive mechanisms deployed by alkaliphiles to circumvent
the challenges and successfully colonize high pH habitats. Most of the studies made
on high pH adaptations of organisms are related to alkaliphilic bacteria, and hence,
the discussion in this chapter largely revolves around this group of organisms. On the
other hand, there are several groups of unicellular and multicellular eukaryotes that
are adapted to alkaline habitats. Studies on high pH adaptations of these eukaryotic
organisms still remain scarce. Here, an effort is made to include the available
information on adaptive mechanisms of multicellular organisms to high pH
environment, fish.
88
G. Mamo
deserts, soda pans, solonchak soils, salt pans, oceans, etc. are known supporting this
remarkable group of organisms [3–7]. Alkaliphiles have also been isolated from the
steady-state alkaline environments that exist in the body of other organisms such
as insect guts [8–10]. Serpentinization, low-temperature weathering of silicate
containing calcium and magnesium minerals like olivine (MgFeSiO 4 ) and pyroxene
(MgCaFeSiO 3 ), forms a highly alkaline Ca
2+ -rich environment [11]. Alkaliphiles
such as Alkaliphilus hydrothermalis [12] and Serpentinicella alkaliphila [13] have
been isolated from such serpentine environments. Anthropogenic activities such as
indigo dye production, potato peeling using KOH, cement/concrete production,
electroplating, leather tanning, paper and board manufacture, mining, and herbicide
manufacturing create alkaline environments [14–18]. Regardless of the difference in
the genesis, chemistry, and stability, all known alkaline environments are inhabited
by alkaliphiles, and this is discussed in detail by Kevbrin [19].
High pH environments are not easy to live in without special adaptations. For
instance, maintaining structural integrity, bioenergetics, and intracellular pH homeostasis are barriers for non-alkaliphiles to survive and thrive in this extreme environment. On the other hand, alkaliphiles evolved adaptive solutions to circumvent
these barriers and thrive lavishly in environments with pH values of up to over
13 [16]. However, adaptation always comes with price. Indeed, there is no single
organism that flourishes in a pH range of 1–13. At least in this case, the rule of nature
seems clear, when an organism evolves adaptations to thrive in specific pH condition
(acidic, neutral, or alkaline), its fitness to live in a habitat of different pH condition
is often compromised. Thus, the adaptation range of alkaliphiles determines their
ability to survive in neutral conditions. As the optimum pH for growth varies among
alkaliphiles, the ability to grow in neutral zone is also different. The growth of
obligate alkaliphiles is compromised around neutral condition. On the other hand,
facultative alkaliphiles can grow at neutral pH but not as lavishly as neutralophiles
[20–22]. Similarly, at or above pH 10, the growth yield of facultative alkaliphiles is
often lower than that of obligate alkaliphiles. This may indicate that alkaliphiles
evolved to colonize high pH environments at a cost of losing growth potency around
neutrality.
This chapter presents the grand challenges of life in high pH environments and
tries to summarize the adaptive mechanisms deployed by alkaliphiles to circumvent
the challenges and successfully colonize high pH habitats. Most of the studies made
on high pH adaptations of organisms are related to alkaliphilic bacteria, and hence,
the discussion in this chapter largely revolves around this group of organisms. On the
other hand, there are several groups of unicellular and multicellular eukaryotes that
are adapted to alkaline habitats. Studies on high pH adaptations of these eukaryotic
organisms still remain scarce. Here, an effort is made to include the available
information on adaptive mechanisms of multicellular organisms to high pH
environment, fish.
88
G. Mamo