The Growth of Bacteria with a Constant Food Supply: I. Preliminary Observations on Bacterium coli

Simulating Genetic Circuits in Bacterial Populations with Growth Heterogeneity

We computationally study genetic circuits in bacterial populations with heterogeneities in the growth rate. To that end, we present a stochastic simulation method for gene circuits in populations of cells and propose an efficient implementation that we call the "Next Family Method". Within this approach, we implement different population setups, specifically Chemostat-type growth and growth in an ideal Mother Machine and show that the population structure and its statistics are different for the different setups whenever there is growth heterogeneity. Such dependence on the population setup is demonstrated, in the case of bistable systems with different growth rates in the stable states, to have distinctive signatures on quantities including the distributions of protein concentration and growth rates, and hysteresis curves. Applying this method to a bistable antibiotic resistance circuit, we find that as a result of the different statistics in different population setups, the estimated minimal inhibitory concentration of the antibiotic becomes dependent on the population setup in which it is measured.

Continuous culture techniques as simulators for standard cells: Jacques Monod's, Aron Novick's and Leo Szilard's quantitative approach to microbiology

Continuous culture techniques were developed in the early twentieth century to replace cumbersome studies of cell growth in batch cultures. In contrast to batch cultures, they constituted an open concept, as cells are forced to proliferate by adding new medium while cell suspension is constantly removed. During the 1940s and 1950s new devices have been designed-called "automatic syringe mechanism," "turbidostat," "chemostat," "bactogen," and "microbial auxanometer"-which allowed increasingly accurate quantitative measurements of bacterial growth. With these devices cell growth came under the external control of the experimenters and thus accessible for developing a mathematical theory of growth kinetics-developed mainly by Jacques Monod, Aron Novick and Leo Szilard in the early 1950s and still in use today. The paper explores the development of continuous culture devices and claims that these devices are simulators for standard cells following specific requirements, in particular involving mathematical constraints in the design and setting of the devices as well as experiments. These requirements have led to contemporary designs of continuous culture techniques realizing a specific event-based flow algorithm able to simulate directed evolution and produce artificial cells and microorganisms. This current development is seen as an alternative approach to today's synthetic biology.

Studies in the dynamics of disinfection: XI. The effect of lethal temperatures on standard cultures of Bact. coli. IV. An investigation of that portion of the population which survives prolonged exposure at pH 7.0

1. An attempt has been made to discover the origin and nature of the small proportion of the cells in standard cultures ofBact. coliwhich is able to withstand, apparently indefinitely, exposure to temperatures of 49, 51 and 53° C.

2. The method adopted was to allow these survivors to generate fresh cultures in the same flask merely by reducing the temperature to 35° C. and to subject the resulting cultures in turn to heat treatment. Only one process of regeneration and subsequent disinfection was carried out at 49 and 53° C., but at 51° C. the process was repeated four times. The disinfection curve was determined on each occasion and the permanent population allowed to become established.

3. Changes in the heat resistance of the cultures were judged by (a) the disinfection times (99·99 % mortality), (b) the maximum death-rates, (c) the levels of the surviving populations and (d) the variations in death-rate with time during each disinfection.

4. Marked fluctuation in numbers of viable cells was observed during each of the phases of permanent surviving population. The exact levels of survivors were therefore uncertain, but after exposure to 49° C. the mean values were not higher than when 53° C. was used, nor was there an increase in the mean numbers of survivors in the successively regenerated cultures.

5. The survivors did not grow when inoculated into either nutrient agar plates or tubes of broth held at the respective high temperatures, although they remained alive and developed readily on being transferred to 35° C.

6. The maximum death-rate decreased and the disinfection time increased markedly after one regeneration of the cultures. The increase in the latter was not wholly due to the decrease in the former, as the death-rates throughout the disinfection of the regenerated culture were lower.

7. After the second regeneration (at 51° C.) the maximum death-rate declined and the disinfection time rose still higher, but the process was reversed after the third and fourth regenerations.

8. The shape of the graph of log survivors against time altered markedly after the second regeneration at 51° C. The initial death-rate was higher but fell sharply to a minimum before rising again to the final maximum.

9. The experimental findings are discussed. An increase in the general heat resistance of these cultures may have occurred as a result of one regeneration, but the technique employed permitted the gradual alteration of the environmental conditions, and this appears to have exerted complex effects on the cultures so that the results of further regenerations are inconclusive.

The growth of bacterial colonies and their viable population

The numerical aspects of bacterial growth have hitherto been investigated chiefly in fluid media and the laws governing the development of bacterial populations in fluid cultures are known in some detail.

PRODUCTION AND PROPERTIES OF 2,3-BUTANEDIOL: XX. INFLUENCE OF THE INOCULUM ON THE AEROBACILLUS POLYMYXA FERMENTATION

Whole wheat fermentations were started with known numbers of Aerobacillus polymyxa in the range from 50 thousand to 4000 million per ml. of mash. Increasing the initial numbers of the bacteria decreased the lag phase and increased the maximum numbers obtained. Although the initial rate of fermentation was increased, all the fermentations were finished at the same time and gave similar yields of 2,3-butanediol.The effects of added nutrients, incubation temperature, aeration, and reduced pressure on bacterial growth in the inoculum media were investigated but none of the treatments used had an appreciable effect on the subsequent fermentation. The use of a backstocking technique appears to be a practical method of inoculation.