82
EDWARD C. CANTINO AND JAMES S. LOVETT
manipulatable system for manufacture of chitin will be of obvious
significance.
Finally, let us compare the 36-48 hour period in the ontogeny of an
RS cell—a period during which it has become committed but has not yet
come of age—with the pre-sporulation stage in a bacterial cell. Just as
chemical changes occur in the differentiating RS cell during this period,
alterations are also detectable in Bacillus mycoides when it undergoes its
early stage of sporulation (Foster and Perry, 1954). From isotopic and
other analyses, it was concluded that considerable breakdown and
resynthesis occurred during this interval which preceded actual formation of the endospore. Although isotopic evidence for turnover in
Blastocladiella
is not available, a considerable body of circumstantial
evidence is.
During this "pre-sporulation' period in RS ontogeny, insoluble
nitrogen steadily increases; it is only partially accounted for by
sedimentable constituents such as chitin, DNA, and a certain fraction of
the RNA. Simultaneously, the cell's pool of soluble nitrogen is cut in
half, and most if not all of this is due to loss of free amino-acids (Lovett
and Cantino, 1960b). This depletion of the amino-acid pool does not
reflect the magnitude of the conversion of nitrogenous constituents to
insoluble materials however, because the increase in the latter is ca.
1-4-fold greater than the decrease in size of the soluble nitrogen pool;
thus, a substantial portion of it is derived from the external medium.
Since total soluble-protein does not change during this time, synthesis
of macromolecular material must take place, along with an unknown
amount of turnover (as reflected, for example, in altered levels of
activities of specific enzymes). The degree to which new synthesis results
from turnover, as distinct from continued uptake from the medium, can
only be determined by appropriate labelling experiments which have
not yet been done. The nature of the insoluble nitrogenous material is
still uncertain. Its suspected fate will be discussed shortly; suffice it to
say for now that it may originate by absorption, dehydration, or
complexing of proteins associated with the RS cell's transition to the
dormant state. All these mechanisms have been proposed in relation to
the genesis of bacterial spores (Doi, 1961, and refs. therein). There is,
however, one obvious difference between the 36-48 hour RS cell and the
pre-sporulating cell of B. mycoides; the former has already become
irreversibly committed to sporulation, while the latter either precedes
or results in the stage of irreversibility.
Clearly, despite some obvious and important differences, the resistant
sporangium of Blastocladiella
shares certain basic characteristics with
the spore of a bacterium. We are regrettably far removed from a satisfactory explanation of dormancy in either case, but the similarities
EDWARD C. CANTINO AND JAMES S. LOVETT
manipulatable system for manufacture of chitin will be of obvious
significance.
Finally, let us compare the 36-48 hour period in the ontogeny of an
RS cell—a period during which it has become committed but has not yet
come of age—with the pre-sporulation stage in a bacterial cell. Just as
chemical changes occur in the differentiating RS cell during this period,
alterations are also detectable in Bacillus mycoides when it undergoes its
early stage of sporulation (Foster and Perry, 1954). From isotopic and
other analyses, it was concluded that considerable breakdown and
resynthesis occurred during this interval which preceded actual formation of the endospore. Although isotopic evidence for turnover in
Blastocladiella
is not available, a considerable body of circumstantial
evidence is.
During this "pre-sporulation' period in RS ontogeny, insoluble
nitrogen steadily increases; it is only partially accounted for by
sedimentable constituents such as chitin, DNA, and a certain fraction of
the RNA. Simultaneously, the cell's pool of soluble nitrogen is cut in
half, and most if not all of this is due to loss of free amino-acids (Lovett
and Cantino, 1960b). This depletion of the amino-acid pool does not
reflect the magnitude of the conversion of nitrogenous constituents to
insoluble materials however, because the increase in the latter is ca.
1-4-fold greater than the decrease in size of the soluble nitrogen pool;
thus, a substantial portion of it is derived from the external medium.
Since total soluble-protein does not change during this time, synthesis
of macromolecular material must take place, along with an unknown
amount of turnover (as reflected, for example, in altered levels of
activities of specific enzymes). The degree to which new synthesis results
from turnover, as distinct from continued uptake from the medium, can
only be determined by appropriate labelling experiments which have
not yet been done. The nature of the insoluble nitrogenous material is
still uncertain. Its suspected fate will be discussed shortly; suffice it to
say for now that it may originate by absorption, dehydration, or
complexing of proteins associated with the RS cell's transition to the
dormant state. All these mechanisms have been proposed in relation to
the genesis of bacterial spores (Doi, 1961, and refs. therein). There is,
however, one obvious difference between the 36-48 hour RS cell and the
pre-sporulating cell of B. mycoides; the former has already become
irreversibly committed to sporulation, while the latter either precedes
or results in the stage of irreversibility.
Clearly, despite some obvious and important differences, the resistant
sporangium of Blastocladiella
shares certain basic characteristics with
the spore of a bacterium. We are regrettably far removed from a satisfactory explanation of dormancy in either case, but the similarities