diversity of the sites of serpentinization, at least some of them, is not inferior to the
phototrophic communities of soda lakes. For “alkalimicrobiologists,” these habitats
are less studied compared to soda lakes, and, obviously, one can expect isolation of
new microbes in the future. Moreover, interest to sites of serpentinization is warmed
up by the observation that their physicochemical conditions resemble to those that are
proposed to exist in the early Earth. Previously, the possible participation of
serpentinization process in the origin of life has been proposed [35–37].
2.2 Ocean
Another geochemical system that has a pH on the alkaline side, although not so high, is
the sea. In public consciousness, the sea is usually not regarded as an alkaline
environment; however, seawater has a pH value of near 8.3, and, formally, sea is a
slightly alkaline environment and, hence, can also be the source of alkaliphiles.
Although the alterations of the pH of seawater in course of the Earth’s evolution is
still a matter of debates, nowadays, the World Ocean secures a slightly alkaline but
rather stable environment, comparable with those in low-mineralized soda lakes. The
first evidence of the presence of alkaliphiles in deep-sea mud samples had been
collected by Horikoshi in the late 1990s of the twentieth century in course of search
for extremophiles living on the ocean floor [38, 39]. Since then, microbiologists have
been isolating various strictly and facultatively aerobic alkaliphiles including the
obligate aerobes Oceanobacillus, O. profundus [40], O. pacificus [41], and an extreme
halotolerant (0–21% (v/w) NaCl) O. iheyensis [42] and species of aerotolerant
Alkalibacterium, A. thalassium, A. pelagium, A. putridalgicola, A. kapii [43], and
A. subtropicum [44]. Alkalibacterium species are often referred to as marine lactic
acid bacteria (lactate is a main product in anaerobic growth) and can be isolated from
decaying marine algae, seagrass, and raw and salted fish. By their alkaliphilicity, they
are distinctly different from common terrestrial lactic acid bacteria, which are acid
tolerant or neutralophilic. To them, one can add psychrotolerant, collagenolytic
Alkalimonas collagenimarina [45]; alkalitolerant, urea-lytic Bacillus nanhaiisediminis
[46]; alkalitolerant species of Idiomarina (all are former Pseudidiomarina),
I. donghaiensis, I. maritima [47], and I. sediminum [48]; and haloalkaliphilic species
of Aliidiomarina, A. taiwanensis [49], non-valid “A. haloalkalitolerans” [50],
A. iranensis [51], A. sedimenti [52], and Salinispirillum marinum [53]. The latter
three species were isolated from a Gomishan wetland located along the eastern shore
of the Caspian Sea in Iran. This area, although of marine origin, is characterized by pH
8.5–9.3. Other examples include facultatively anaerobic Alkalimarinus sediminis [54]
and strictly aerobic, alkalitolerant Alkalimicrobium pacificum [55]. Strictly anaerobic
alkaliphiles of marine origin except for those who inhabit submarine serpentinization
sites has not been isolated yet. Considering the global scale of the world oceans, we
should expect more descriptions of new marine alkaliphiles.
60
V. V. Kevbrin
phototrophic communities of soda lakes. For “alkalimicrobiologists,” these habitats
are less studied compared to soda lakes, and, obviously, one can expect isolation of
new microbes in the future. Moreover, interest to sites of serpentinization is warmed
up by the observation that their physicochemical conditions resemble to those that are
proposed to exist in the early Earth. Previously, the possible participation of
serpentinization process in the origin of life has been proposed [35–37].
2.2 Ocean
Another geochemical system that has a pH on the alkaline side, although not so high, is
the sea. In public consciousness, the sea is usually not regarded as an alkaline
environment; however, seawater has a pH value of near 8.3, and, formally, sea is a
slightly alkaline environment and, hence, can also be the source of alkaliphiles.
Although the alterations of the pH of seawater in course of the Earth’s evolution is
still a matter of debates, nowadays, the World Ocean secures a slightly alkaline but
rather stable environment, comparable with those in low-mineralized soda lakes. The
first evidence of the presence of alkaliphiles in deep-sea mud samples had been
collected by Horikoshi in the late 1990s of the twentieth century in course of search
for extremophiles living on the ocean floor [38, 39]. Since then, microbiologists have
been isolating various strictly and facultatively aerobic alkaliphiles including the
obligate aerobes Oceanobacillus, O. profundus [40], O. pacificus [41], and an extreme
halotolerant (0–21% (v/w) NaCl) O. iheyensis [42] and species of aerotolerant
Alkalibacterium, A. thalassium, A. pelagium, A. putridalgicola, A. kapii [43], and
A. subtropicum [44]. Alkalibacterium species are often referred to as marine lactic
acid bacteria (lactate is a main product in anaerobic growth) and can be isolated from
decaying marine algae, seagrass, and raw and salted fish. By their alkaliphilicity, they
are distinctly different from common terrestrial lactic acid bacteria, which are acid
tolerant or neutralophilic. To them, one can add psychrotolerant, collagenolytic
Alkalimonas collagenimarina [45]; alkalitolerant, urea-lytic Bacillus nanhaiisediminis
[46]; alkalitolerant species of Idiomarina (all are former Pseudidiomarina),
I. donghaiensis, I. maritima [47], and I. sediminum [48]; and haloalkaliphilic species
of Aliidiomarina, A. taiwanensis [49], non-valid “A. haloalkalitolerans” [50],
A. iranensis [51], A. sedimenti [52], and Salinispirillum marinum [53]. The latter
three species were isolated from a Gomishan wetland located along the eastern shore
of the Caspian Sea in Iran. This area, although of marine origin, is characterized by pH
8.5–9.3. Other examples include facultatively anaerobic Alkalimarinus sediminis [54]
and strictly aerobic, alkalitolerant Alkalimicrobium pacificum [55]. Strictly anaerobic
alkaliphiles of marine origin except for those who inhabit submarine serpentinization
sites has not been isolated yet. Considering the global scale of the world oceans, we
should expect more descriptions of new marine alkaliphiles.
60
V. V. Kevbrin