160
ROBINA B. SCHOLES AND J. M. SHEWAN
long been known that in these organisms it is thc + ions which are
absolutely required. In other words although C1- can be replaced to
some extent by SO,-- and NO,-, Na+ cannot be replaced by K+,
Rb+, Cs+ or Li+. The obvious explanation that some of the essential
enzymes are Na+ activated does not seem to have been proved (Larsen,
1962). Recent work by Drapeau and MacLeod (1963) seems to indicate
that Na ions are involved in the active transport of substrates into the
cell. They found that the uptake of l*Ca-amino isobutyrate by a marine
Pseudomow sp. was increased one hundred fold in the presence of
NaCl, 200 m M Na+ being the optimal concentration. Thus Na+ plays a
role in these bacterial species similar to that observed in certain animal
tissues (see Drapeau and MacLeod, 1963) and a halophile may be regarded as a bacterium having a Na+-dependent permease system.
The function of Ca and Mg in bacteria having absolute requirements
for these ions still remains unanswered but may be related to the structure and stability of the cell wall.
B. Barophiles
It is not surprising that in an environment where enormous hydrostatic pressures exist, some bacteria can be isolated which survive or
even prefer these unusual conditions. ZoBell and Johnson (1949) were
the first to describe such organisms and others have subsequently been
isolated or studied by ZoBell and his co-workers (ZoBell and Oppenheimer, 1950 ; ZoBell and Morita, 1967) ; and by Kriss (1963). As might
be expected bacteria isolated from or near the surface seem to have the
same tolerance to hydrostatic pressures as terrestrial strains, being
inhibited at pressures of about 200-400 atm, and killed by pressures
beyond 600 to 600 atm. Barophiles have been isolated both in sea
water and muds mainly from depths greater than lOOOm, as in the
various trenches in the Pacific. They appear to consist mostly of
Gram-negative rods of the Pseudomonas group (e.g. Pseudomonas
zunthrocus of ZoBell and Johnson, 1949). As Kriss (1963) points out,
many barotolerant forms exist not only in the sea but also in the soil,
and include not only Gram-negative asporogenous rods but also sporebearing Bacillus spp., cocci and mycobacteria. If true barophilic
microorganisms do exist, no explanation has yet been forthcoming of
the mechanism of their adaptation to high pressures.
C. Psychrophiles
It has long been known that many marine microorganisms such &8
the luminous bacteria (Forster, 1887) grow well at temperatures in the
region of 0°C even although their optima are near 20°C. The term
ROBINA B. SCHOLES AND J. M. SHEWAN
long been known that in these organisms it is thc + ions which are
absolutely required. In other words although C1- can be replaced to
some extent by SO,-- and NO,-, Na+ cannot be replaced by K+,
Rb+, Cs+ or Li+. The obvious explanation that some of the essential
enzymes are Na+ activated does not seem to have been proved (Larsen,
1962). Recent work by Drapeau and MacLeod (1963) seems to indicate
that Na ions are involved in the active transport of substrates into the
cell. They found that the uptake of l*Ca-amino isobutyrate by a marine
Pseudomow sp. was increased one hundred fold in the presence of
NaCl, 200 m M Na+ being the optimal concentration. Thus Na+ plays a
role in these bacterial species similar to that observed in certain animal
tissues (see Drapeau and MacLeod, 1963) and a halophile may be regarded as a bacterium having a Na+-dependent permease system.
The function of Ca and Mg in bacteria having absolute requirements
for these ions still remains unanswered but may be related to the structure and stability of the cell wall.
B. Barophiles
It is not surprising that in an environment where enormous hydrostatic pressures exist, some bacteria can be isolated which survive or
even prefer these unusual conditions. ZoBell and Johnson (1949) were
the first to describe such organisms and others have subsequently been
isolated or studied by ZoBell and his co-workers (ZoBell and Oppenheimer, 1950 ; ZoBell and Morita, 1967) ; and by Kriss (1963). As might
be expected bacteria isolated from or near the surface seem to have the
same tolerance to hydrostatic pressures as terrestrial strains, being
inhibited at pressures of about 200-400 atm, and killed by pressures
beyond 600 to 600 atm. Barophiles have been isolated both in sea
water and muds mainly from depths greater than lOOOm, as in the
various trenches in the Pacific. They appear to consist mostly of
Gram-negative rods of the Pseudomonas group (e.g. Pseudomonas
zunthrocus of ZoBell and Johnson, 1949). As Kriss (1963) points out,
many barotolerant forms exist not only in the sea but also in the soil,
and include not only Gram-negative asporogenous rods but also sporebearing Bacillus spp., cocci and mycobacteria. If true barophilic
microorganisms do exist, no explanation has yet been forthcoming of
the mechanism of their adaptation to high pressures.
C. Psychrophiles
It has long been known that many marine microorganisms such &8
the luminous bacteria (Forster, 1887) grow well at temperatures in the
region of 0°C even although their optima are near 20°C. The term