Evolution of Fusarium graminearum A3/5 grown in a glucose-limited chemostat culture at a slow dilution rate

Abstract

The evolution of Fusarium graminearum A3/5 grown in a glucose-limited chemostat at a dilution rate of 0 0 5 h-l (doubling time of 13.9 h) was followed for 957 h or 69 generations. Periodic selection of advantageous mutants was monitored in the culture by determining increases and decreases in the concentration of cycloheximide-resistant macroconidia in the population. Six peaks in the concentration of cycloheximide-resistant macroconidia were observed representing five adaptive changes in the population; on average, an adaptive change occurred once every 148 _+ 22 h (mean & SE). The selection coefficient of strains present at the start of each increase in the concentration of cycloheximide-resistant macroconidia (i.e. after the establishment of a new advantageous strain) was determined relative to A3/5 and was found to increase progressively with time. When grown at a dilution rate of 0 0 5 h-l, the strain (A28-5) isolated from the last adaptive peak had a selection coefficient of 0.023 h-' relative to A3/5, but A28-S lost its selective advantage when grown at a dilution rate of about 0.11 h-' and was at a selective disadvantage when grown at a dilution rate higher than 0.1 1 h-l. The K,,, value (12 _+ 5 pM) for uptake of glucose by A 2 8 4 was significantly lower than that for A3/5. The spontaneous mutation rate from cycloheximide sensitivity to cycloheximide resistance was estimated to be 1.8 (k0.2) x generation-l.The culture initially contained about 1 x lo6 macroconidia ml-l but this decreased with time until, at about 800 h, the culture contained only about 1 x 104 macroconidia ml-l. No highly branched (colonial) mutants were observed in glucose-limited cultures at dilution rates of 0 0 5 h-l, even though the evolution of the population was followed for a further 1345 h in a second chemostat, making a total evolutionary period of 2207 h or 159 generations.h-l or 2.5 x

Transcriptional monitoring of steady state and effects of anaerobic phases in chemostat cultures of the filamentous fungus Trichoderma reesei

“…The filamentous growth form increases the viscosity of the culture, causing mass transfer limitations [ 11 , 12 ]. As with other organisms culture evolution as a result of mutations and selection occurs [ 13 ].…”

Development of Efficient Xylose Fermentation in Saccharomyces cerevisiae: Xylose Isomerase as a Key Component

“…Soon after the invention of the chemostat it was already established that prolonged cultivation in nutrient-limited chemostats leads to selection of spontaneous mutants with an improved affinity for the growth-limiting nutrient [52,53]. This principle, which has since been demonstrated for many micro-organisms and nutrients [40,58,72,73] was applied to improve the affinity of S. cerevisiae RWB 217 for d-xylose [44].…”