CSs
Compatible solutes
EMP
Embden–Meyerhof–Parnas
EPS
Exopolysaccharides
HMP
Hexose monophosphate
MRSA
Methicillin-resistant Staphylococcus aureus
NAD(P) Nicotinamide adenine dinucleotide (phosphate)
NMR
Nuclear magnetic resonance
OFAT
One-factor-at-a-time technique
PHA
Polyhydroxyalkanoate
PHB
Poly-beta-hydroxybutyrate
pH i
Intracellular pH
pH o
Outside (extracellular) pH
TCA
Tricarboxylic acid
WIPO
World Intellectual Property Organization
1 Introduction
The group of alkaliphilic microbes growing well above pH 9 is practically as diverse
as microbes living in neutral habitats: there are facultative and obligate, aerobic and
anaerobic, methanogens, cyanobacteria, and sulfur-oxidizing alkaliphiles. However,
the diversity of alkaliphiles on earth may account for only a few percentages of the
total microbes. Some alkaliphiles are adapted to other environmental extremes (dual
or poly extremophiles) like groups referred to as halo-, thermo-, psychrophilic, and
alkaliphilic photosynthetic microbes as reviewed by Horikoshi [1]. To keep the
present overview focused to biotechnological aspects, alkaliphiles are dealt here
with seemingly as one group, despite their enormous diversity.
The intracellular pH (pH i ) of alkaliphiles can be 1–3 units lower than that of the
outside (extracellular) pH (pH o ). Therefore, the chemical milieu for biomolecules
inside and outside of the microbial cell can be very different. The pH optimums of
many internal enzymes of alkaliphiles are, however, higher than those from
neutralophiles, showing that also internal metabolism has adapted to functioning at
higher pH, up to 9.5 [1] which means that the inside proton concentration can be
>100 times less than that of the neutral (and hydroxide ions correspondently higher)
condition. Most enzyme reactions involve protons in one or another form. Thus,
enzymes of internal metabolism must have adapted to function in a low proton
concentration. Without such adaptation, they should have had to accept drastically
lower specific activity, which should be seen in retardation of the growth and other
metabolic activities; the fact that does not seem to be valid. The cells of alkaliphiles
shall communicate chemically with their environment. This means that nutrients
must be transferred from higher to lower pH and products to opposite direction. In
the growth medium, there lie potential problems, as well. For example, amino groups
are fully deprotonated at pH, say, 10–12 and exist as very reactive nucleophiles,
Metabolites Produced by Alkaliphiles with Potential Biotechnological. . .
159
Compatible solutes
EMP
Embden–Meyerhof–Parnas
EPS
Exopolysaccharides
HMP
Hexose monophosphate
MRSA
Methicillin-resistant Staphylococcus aureus
NAD(P) Nicotinamide adenine dinucleotide (phosphate)
NMR
Nuclear magnetic resonance
OFAT
One-factor-at-a-time technique
PHA
Polyhydroxyalkanoate
PHB
Poly-beta-hydroxybutyrate
pH i
Intracellular pH
pH o
Outside (extracellular) pH
TCA
Tricarboxylic acid
WIPO
World Intellectual Property Organization
1 Introduction
The group of alkaliphilic microbes growing well above pH 9 is practically as diverse
as microbes living in neutral habitats: there are facultative and obligate, aerobic and
anaerobic, methanogens, cyanobacteria, and sulfur-oxidizing alkaliphiles. However,
the diversity of alkaliphiles on earth may account for only a few percentages of the
total microbes. Some alkaliphiles are adapted to other environmental extremes (dual
or poly extremophiles) like groups referred to as halo-, thermo-, psychrophilic, and
alkaliphilic photosynthetic microbes as reviewed by Horikoshi [1]. To keep the
present overview focused to biotechnological aspects, alkaliphiles are dealt here
with seemingly as one group, despite their enormous diversity.
The intracellular pH (pH i ) of alkaliphiles can be 1–3 units lower than that of the
outside (extracellular) pH (pH o ). Therefore, the chemical milieu for biomolecules
inside and outside of the microbial cell can be very different. The pH optimums of
many internal enzymes of alkaliphiles are, however, higher than those from
neutralophiles, showing that also internal metabolism has adapted to functioning at
higher pH, up to 9.5 [1] which means that the inside proton concentration can be
>100 times less than that of the neutral (and hydroxide ions correspondently higher)
condition. Most enzyme reactions involve protons in one or another form. Thus,
enzymes of internal metabolism must have adapted to function in a low proton
concentration. Without such adaptation, they should have had to accept drastically
lower specific activity, which should be seen in retardation of the growth and other
metabolic activities; the fact that does not seem to be valid. The cells of alkaliphiles
shall communicate chemically with their environment. This means that nutrients
must be transferred from higher to lower pH and products to opposite direction. In
the growth medium, there lie potential problems, as well. For example, amino groups
are fully deprotonated at pH, say, 10–12 and exist as very reactive nucleophiles,
Metabolites Produced by Alkaliphiles with Potential Biotechnological. . .
159