Single-stage Continuous Culture Research Articles

The macromolecular composition of Geotrichum candidum grown on whiskey distillery spent wash

Biomass harvested from batch and single-stage continuous cultures of the fungus Geotrichum candidum, growing on the spent wash from an Irish malt whiskey distillery, was analysed for macromolecular components. The ‘true’ protein content was on average more than 47% (w/w), while ‘crude’ protein levels of as much as 61% were found. The protein was not deficient in any amino acid when compared to the FAO standard. The effects of varying growth temperature and dilution rate on the composition of the organism are discussed, and also the problem of its accumulation of copper from the medium.

Exopolysaccharide production by Pseudomonas NCIB11264 grown in continuous culture.

Exopolysaccharide formation by Pseudomonas NCIB11264 in a single-stage continuous culture was maximal under nitrogen limitation with excess carbohydrate substrate at 30 +/- 1 degrees C and pH 7.0 +/- 0.1. Polysaccharide production was not enhanced by phosphate limitation but was dependent on the dilution rate. Steady states were maintained for up to 500 h without deterioration of the culture or the development of mutant strains. The efficiency of conversion of the glucose substrate utilized into exopolysaccharide by the chemostat cultures was as high as 73%.

Lipid accumulation in an oleaginous yeast (Candida 107) growing on glucose in single-stage continuous culture.

Lipid accumulation of Candida 107, grown at dilution rates from 0.03 to the maximum of 0.21/h, with carbon, nitrogen, phosphate, and magnesium limitations in a chemostat, was maximal at about 40% (wt/wt) with nitrogen-limited medium at a dilution rate of 0.06/h, giving an efficiency of substrate conversion of 22 g of lipid per g of glucose consumed. At higher dilution rates the lipid content decreased. With carbon-limited growth, the highest lipid content (14%, wt/wt) was at the maximum dilution rate. High lipid contents also occurred with phosphate + nitrogen as double limitations of growth, with the lipid content of the yeast (about 35%, wt/wt) continuing to be near maximum at dilution rates also near maximum (0.17/h), thus giving the highest specific rate of lipid formation of any growth conditions (0.59 g of lipid/g of yeast per h). However, the efficiency of substrate utilization was only 5.2 g of lipid formed per 100 g of glucose consumed. The composition of the fatty acyl residues within the lipid remained constant over many weeks if the steady-state conditions remained unchanged. With carbon-limited growth, the degree of unsaturation of the fatty acids markedly decreased as the dilution rate was increased, but with nitrogen limitation the reverse trend was seen. In all cases, linoleic and oleic acids were the principal fatty acyl residues affected, and their relative proportions always varied in opposite directions. When magnesium was a limiting nutrient, there was a considerable increase in the proportion of myristic acid produced within the lipid. Neutral lipids (predominantly triglycerides) varied from 66 to 92% of the total lipid from carbon- and nitrogen-limited growth; phospholipids (varying from 2 to 25%) were highest in nitrogen-limited growth. The fatty acyl residues within each lipid fraction showed the same variations with changing growth rates.

Production of gramicidin S in batch and continuous culture.

AbstractA mathematical model for the production of gramicidin S in batch and continuous culture is proposed. It is based on the division of the age of a cell into two phases—an immature and a mature one. A nongrowth associated product, such as an antibiotic, is assumed to be produced when the organism is in the older of these two phases, the mature state. The parameters describing the model were evaluated from batch and single stage transient continuous culture of Bacillus brevis, which produces the antibiotic gramicidin S. The predictive value of the model was studied in steady‐state single stage continuous culture and in a transient two stage system. Good agreement between the theoretical curves and the experimental results was found in the transient response of both the first and second stage systems, although at high dilution rates (0.34 hr−1) in the first stage, deviations from the predicted response were observed in the second stage. These may have been due to chemostat instability at dilution rates close to washout, lags in cell growth, and a metabolic lag on going from stage one to stage two.

Growth and physiology of a yeast cultivated in batch and continuous culture systems.

Inoculum size has been found to affect significantly the maximum attainable specific growth rate during batch cultivation ofCandida utilis. Lower inoculum size resulted in an increased growth rate and relatively longer lag. The culture is found to be most active in the beginning of the exponential phase as regards its RNA synthesis rate. Batch data were used for predicting the conditions of the yeast population in single-stage continuous culture system. Predicted and the experimental values showed a reasonable agreement. In single-stage chemostat the physiology of the yeast was studied on the basis RNA, DNA and protein synthesis rates at various growth rates. The results indicate that the productivity of cells and the rate of synthesis of macromolecules is highest at the dilution rate values of 0.33 to 0.35 hr−1. In order to attain so-called unrestricted conditions of growth a pluristage pluristream continuous system was employed. It is assumed that under such conditions the specific growth rate and the synthetic activity of yeasts may reach its maximum on a given medium. The results presented do not show such conditions of growth under the experimental conditions employed (D1=0.35 hr−1 andD2=0.2 to 1.7 hr−1) withCandida utilis cultivated on beet molasses medium. Second stage of a two-stage two-stream continuous system is constantly fed with the cells from the foregoing stage; this category of cells on entering the new conditions of the second stage is expected to show some adaptation period. Experiments are reported to this effect.