Influence of age of parent culture on size of cells of Bacillus megatherium.

Abstract

In a previous communication 1 I have pointed out that during the early hours of a culture the cells of Bacillus megatherium become greatly increased in size and then rapidly decrease; that the increase in size is accompanied by increased variability, the frequency curves showing skewness and a tendency to bimodality; and that the degree of duration of the increase in size is greater with smaller seedings. These observations were made on cultures inoculated from a culture 12 hours old, i. e., one which had already reached the maximum of growth. In the present study I have observed the variations in size in cultures transplanted from a parent culture after 2, 4, 6 and 8 hours of growth, i. e., during the period when the cells were increasing and decreasing in size.

In the accompanying graphs the solid lines indicate the average length of the cells, the broken lines the coefficient of variation. The abscissæ indicate the age of the cultures in hours, the ordinates to the left length of cells in microns, those to the right coefficients of variation. The curves for the parent culture are repeated in the graphs for the various subcultures up to the time of transplanting.

When transplanted during the period of increasing size, at 2 hours, or at the time of maximum size, at 4 hours, the organisms continued to increase in size. It is noteworthy that the greatest decrease in size in these subcultures occurred between the 5th and 6th hours, as was also the case with the parent culture. The entire curves for these two subcultures, including the time spent in the parent culture, bear the same relationship to the parent culture as do curves obtained from cultures with small inoculums to cultures more heavily seeded; there is a greater increase in size over a longer period of time.