Maintenance requirements for bacteria growing on C1-compounds

The maintenance coefficient, ms (mmol substrate/g cell dry wt hr), of two distinct groups of C1-utilizing bacteria has been determined by growing the organisms in an aerobic continuous culture limited by different C1 growth substrates. For growth on methanol, ms = 2.5 +/- 0.3 for Pseudomonas C; 3.9 +/- 0.7 for Ps. methylotropha (these bacteria utilize methanol via the ribulose monophosphate pathway of formaldehyde fixation); 1.5 +/- 0.2 for Pseudomonas 1, and 2.3 +/- 0.4 for Pseudomonas 135 (the latter bacteria utilize C1-compounds via the serine pathway). For growth on formaldehyde, ms = 1.5 +/- 0.3 for Pseudomonas 1 and 2.7 +/- 0.7 for Pseudomonas 135, whereas on formate the values for ms are 1.0 +/- 0.2 and 4.4 +/- 1.3; respectively. Although the maintenance coefficients did not differ systematically between the two groups of bacteria, the maintenance requirements per generation of the serine pathway bacteria were considerably higher (8.7 vs. 3.9) owing to their slower growth rate. The maximum molar yield values, YMmax (g cell dry wt/mol substrate utilized), corrected for the maintenance energy of bacteria which utilize C1-compounds via the ribulose monophosphate pathway averaged 19.1 when grown on methanol, while the values for bacteria which use the serine pathway averaged 13.5. On formaldehyde an average value of 11.5 is obtained and on formate the average value was 7.4 in the serine pathway bacteria.     

Transient response of continuous cultures to changes in temperature

The purpose of this experimental study was to examine the transient response of a chemostat-type continuous culture of Escherichia coli B to step changes in temperature by following transient limiting substrate concentration and calculating from it the transient growth rate. The transient response to step changes of temperature was tested for four different situations. In the first two cases, temperature was shifted down from 37 to 27°C., and 37 to 32°C. In the last two, it was shifted up from 32 to 37°C., and 27 to 37°C. When the temperature was shifted up, the growth rate increased rather rapidly to its transient maximum value and then decreased slowly until it, settled back into the steady-state value. On the other hand, when the temperature was shifted down, the growth rate decreased relatively rapidly to its transient minimum and then it slowly increased and returned gradually to the steady-state value. The magnitude of the transients was less than would be expected if the transient growth rates followed an Arrhenius function.     

The effect of exogenous catalase on the aerobic growth of clostridia

The results obtained by Holman (1955) indicating a marked protective effect of catalase on clostridia growing aerobically were shown to be due to impurities in the catalase preparation used. In aerobic liquid shake flask cultures, no stimulation of growth by crystalline catalase could be demonstrated, although withLactobacillus acidophilus andL. leichmannii a marked effect was observed.Contribution no. 530 from the Department of Nutrition and Food Science, Massachusetts Institute of Technology.     

Measurement of heat evolution and correlation with oxygen consumption during microbial growth

A procedure for measuring the rate of heat production from a fermentation has been developed. The method is based on measuring the rate of temperature rise of the fermentation broth resulting from metabolism, when the temperature controller is turned off. The heat accumulation measured in this manner is then corrected for heat losses and gains. A sensitive thermistor is used to follow the temperature rise with time. This procedure is shown to be as accurate as previous methods but much simpler in execution. Using this technique, the rate of heat production during metabolism was found to correlate with the rate of oxygen consumption. Experiments were performed using bacteria (E. coli and B. subtilis), a yeast (C. intermedia), and a mold (A. niger). The substrates investigated included glucose, molasses, and soy bean meal. The proportionality constant for the correlation is independent of the growth rate, slightly dependent on the substrate, and possibly dependent On the type of organism growth. This correlation has considerable potential for predicting heat evolution from the metabolism of microorganisms on simple or complex substrates and providing quantitative parameters necessary for heat removal calculations.     

Tryptophan- and indole-excreting prototrophic mutant of Escherichia coli

Lim, P. G. (Massachusetts Institute of Technology, Cambridge), and R. I. Mateles. Tryptophan- and indole-excreting prototrophic mutant of Escherichia coli. J. Bacteriol. 87:1051-1055. 1964.-A mutant of Escherichia coli K-12, capable of excreting 350 mg of indole and 50 mg of tryptophan per liter when grown on minimal medium, was found to have a level of 3-deoxy-d-arabino-heptulosonic acid-7-phosphate (DAHP) synthetase 60% higher than the parent, and to have a 10- to 15-fold elevation of the levels of enzymes in the tryptophan branch of the pathway for aromatic amino acid biosynthesis. Contrary to what previous investigators found in E. coli W, the presence of a tyrosine-repressible component of DAHP synthetase sensitive to end-product inhibition by tyrosine could not be demonstrated in either strain K-12 or the mutant. The mutant strain is an example of a microorganism which excretes biosynthetic end products solely because of genetic derepression, as opposed to most previously reported amino acid accumulators which require a combination of genetic and physiological manipulation to achieve derepression.