SYMPOSIUM ON INITIATION OF BACTERIAL GROWTH1 IV. DORMANCY, GERMINATION, AND OUTGROWTH

The bacterial spore is the most nearly inert icals are also released to the surrounding meliving cell known, and yet it responds rapidly to dium, notably the spore peptide, a number of unique trigger mechanisms that initiate growth. amino acids, and other substances as yet unidenIt is intended to discuss here some of the charactified. The DPA is therefore probably complexed teristics of these cells as well as some factors with the peptide and other substances in the involved in the trigger mechanism and the initial spore. growth that results. Church and Halvorson (8) and unpublished The resistance of these unique cells to heat and results of the writer and G. G. K. Murty have injurious chemicals is well known and needs no been able to produce sporelike structures that comment. However, the fact that the mechado not contain DPA, or that contain less than nism of resistance is so little understood reflects the normal amount. Cells having no DPA are our lack of knowledge of the composition and as heat sensitive as vegetative cells, and those organic structure of the cells. Some progress in having reduced amounts have a reduced heat this connection is evident from recent researches resistance. In fact, over a certain range of conwhich have revealed a few substances that are centration, there appears to be a direct correlaabundantly present in spores but absent in the tion between heat resistance and the DPA concorresponding vegetative cells. Notable among tent. These facts indicate that this acid, as it is these are dipicolonic acid (DPA) revealed by complexed in the cell, is somehow responsible Powell (1), a special spore peptide revealed by for the resistance of the spores. To date little Strange and Powell (2), and several heat-reprogress has been made in elucidating the nature sistant enzymes reported by the Illinois group, of this complex because mechanical rupture of Stewart and Halvorson (3), Lawrence and Halthe cell produces the same result as germination, vorson (4), Lawrence (5), and Nakata (6). and no one has yet found a way of preserving DPA has been demonstrated in all spores, both the complex while mechanically rupturing the aerobic and anaerobic, that have been studied cell. to date. It has never been found in vegetative Cytological studies on the spore have revealed a cells, but is present in spores to the extent of structure quite different from that of the vegefrom 6 to 12 per cent of the dry weight of the tative cell. This has been studied extensively by cells. Although DPA itself is readily water Robinow and Fitz-James (9) but time does not soluble, it can be extracted from spores only by permit a review of their work here. Suffice it to means of digestion with strong mineral acid. say that marked changes take place in the spore It is synthesized late in the process of sporulation. structure during germination and during the In the case of anaerobic sporeformers, Collier release of the DPA and spore peptide, indicating (7) has shown that it is produced after the sporea relationship between the structure as seen in like structure is formed. When the spore germicytological studies and the biochemical changes nates, the DPA is released into the medium. occurring during germination. It is apparent, therefore, that the DPA must Although the spores are in most respects inert, be tied up in some insoluble structure. When several active enzymes have been clearly demongermination takes place, a number of other chemstrated in the intact heat-resistant cell. Stewart