THE PRESENT STATUS OF SOME ASPEUTS OF MARINE MIOROBIOLOOY
149
least two groups of organisms, one consisting of Gram-negative, asporogenous, polar flagellated rods and generally classified aa Halobacteriurn
spp. ; the other belonging to the Hicrococcus or Sarcina groups. Their
exact taxonomic positions, particularly of the Halobacterium spp. are,
however, still in dispute.
Most marine bacteria, however, are either halotolerant or slightly to
moderately halophilic and comprise species belonging to most of the
genera mentioned earlier, but they grow best in sea water media or in an
isotonic mineral solution.
The questions why some bacteria can tolerate large amounts of
salts and why some have an absolute requirement for Na+ and possibly
other ions still remain unanswered. So far as the halotolerant and
extreme halophiles are concerned, it appears that with many species
Na+ and C1- can be replaced, in part a t least, by other ions, such &s
Kf or Mgff, SO,--, or Br-. Much work has been done on these problems since 1946, more particularly by Gibbons and his school with the
extreme halophiles, by MacLeod and his co-workers in Canada, and by
Pratt in U.S.A. with marine bacteria. The hypothesis that bacteria
tolerate high concentrations of salt owing to a property of the cell
wall which prevents the build up of salt concentration within the cell
was disproved by Gibbons and Baxter (1953) who found that using
both extreme and moderate halophiles the internal and external salts
concentrations were approximately equivalent. An important finding
(Christian, 1956) that K+ tends to accumulate preferentially within the
cell may be related to the importance of this ion in enzyme activation.
Later work by Gibbons and his co-workers in which a variety of enzyme
systems such as glycerol dehydrogenase, isocitric dehydrogenase,
and cytochrome oxidase, were investigated in both halophiles and nonhalophiles, showed that these enzyme systems were more active in the
halophiles at higher salt concentrations, and some would not function
in the absence of salt or were irreversibly inactivated in low concentrations of salt. It has been concluded, therefore, that the halotolerant
group can grow in the presence of high concentrations of salt because of
modifications and/or adaptation of the enzyme systems; and Baxter
(1959) believed, as a working hypothesis, that these enzymes differ from
others in being rather loosely held in the native, enzymically active
conformation, so that it is only when the intra-molecular electrostatic repulsions are reduced by the presence of salt that they are able
to assume the structure in which they act as catalysfs.
It still has to be explained, however, why some organisms have an
absolute requirement for certain salts and here again, while no complete
answer can yet be given, considerable progress has been made. It has
149
least two groups of organisms, one consisting of Gram-negative, asporogenous, polar flagellated rods and generally classified aa Halobacteriurn
spp. ; the other belonging to the Hicrococcus or Sarcina groups. Their
exact taxonomic positions, particularly of the Halobacterium spp. are,
however, still in dispute.
Most marine bacteria, however, are either halotolerant or slightly to
moderately halophilic and comprise species belonging to most of the
genera mentioned earlier, but they grow best in sea water media or in an
isotonic mineral solution.
The questions why some bacteria can tolerate large amounts of
salts and why some have an absolute requirement for Na+ and possibly
other ions still remain unanswered. So far as the halotolerant and
extreme halophiles are concerned, it appears that with many species
Na+ and C1- can be replaced, in part a t least, by other ions, such &s
Kf or Mgff, SO,--, or Br-. Much work has been done on these problems since 1946, more particularly by Gibbons and his school with the
extreme halophiles, by MacLeod and his co-workers in Canada, and by
Pratt in U.S.A. with marine bacteria. The hypothesis that bacteria
tolerate high concentrations of salt owing to a property of the cell
wall which prevents the build up of salt concentration within the cell
was disproved by Gibbons and Baxter (1953) who found that using
both extreme and moderate halophiles the internal and external salts
concentrations were approximately equivalent. An important finding
(Christian, 1956) that K+ tends to accumulate preferentially within the
cell may be related to the importance of this ion in enzyme activation.
Later work by Gibbons and his co-workers in which a variety of enzyme
systems such as glycerol dehydrogenase, isocitric dehydrogenase,
and cytochrome oxidase, were investigated in both halophiles and nonhalophiles, showed that these enzyme systems were more active in the
halophiles at higher salt concentrations, and some would not function
in the absence of salt or were irreversibly inactivated in low concentrations of salt. It has been concluded, therefore, that the halotolerant
group can grow in the presence of high concentrations of salt because of
modifications and/or adaptation of the enzyme systems; and Baxter
(1959) believed, as a working hypothesis, that these enzymes differ from
others in being rather loosely held in the native, enzymically active
conformation, so that it is only when the intra-molecular electrostatic repulsions are reduced by the presence of salt that they are able
to assume the structure in which they act as catalysfs.
It still has to be explained, however, why some organisms have an
absolute requirement for certain salts and here again, while no complete
answer can yet be given, considerable progress has been made. It has