Periodic selection in longterm continuous-flow cultures of the filamentous fungus Fusarium graminearum

Abstract

By monitoring increases and decreases in the proportion of cycloheximide-resistant macroconidia, periodic selection was observed in populations of the filamentous fungus Fusarium graminearurn, grown in glucose-limited chemostat cultures. The results indicated that periodic selection of advantageous mutants of F. graminearurn occurred at intervals of about 124 h at both high (D = 0.19 h-', approximately 34 generations) and low (D = 0-06 h-', approximately 11 generations) dilution rates. Several 'adaptive' peaks (each indicating the appearance of an advantageous mutation) were observed before morphological (highly branched) mutants appeared in the populations; these mutants have previously been observed to have a selective advantage over the parental strain. At intervals, macroconidia harvested from the chemostat were used to inoculate plates of non-antibioticcontaining agar medium, and it was possible to monitor periodic selection in the original chemostat culture using second generation macroconidia harvested from these cultures. The proportion of cycloheximide-, potassium chlorate-, and p-fluoro-DL-phenylalanine-resistant macroconidia in these second generation macroconidia changed in a pattern similar to that observed when monitoring the proportion of cycloheximide-resistant macroconidia in the first generation population harvested directly from the chemostat. The experiments demonstrated that populations of filamentous fungi are heterogeneous and that much of this heterogeneity may already be present at the end of batch growth, i.e. before the onset of continuous cultivation.

Improvement of antibiotic titers fromStreptomyces bacteria by interactive continuous selection

“…Dykhuizen and Hartl13 showed this to be the case by numerical simulation. Wiebe et al 42 used a similar analysis to investigate the selection and origin of colonial mutants of the filamentous fungus Fusarium grarninarium during chemostat culture.…”

Isolation of a fluffy mutant of Aspergillus niger from chemostat culture and its potential use as a morphologically stable host for protein production

“…A major problem in the use of continuous cultures is the rapid appearance of morphological mutants, often leading to a reduction in protein production and altered growth characteristics (Christensen et al, 1995;Mainwaring et al, 1999;Wiebe et al, 1994;Withers et al, 1998). The mutants were affected in sporulation, branching, or both Wiebe et al, 1993;Withers et al, 1995) and were often demonstrated to have a selective advantage over the parental strain. Also, nonmorphological mutations with altered production characteristics may occur (Mainwaring et al, 1999;Pederson et al, 2000;Wiebe et al, 1996).…”

Use of a series of chemostat cultures to isolate 'improved' variants of the Quorne myco-protein fungus, Fusarium graminearum A3/5

“…In glucose-limited chemostat culture, the interval between the onset of continuous flow and the first (adaptive) peak of cycloheximide-resistant macroconidia was longer (384 h) for A23-S than that observed in the parental strain (longest interval = 171 h, Wiebe et a/., 1993), suggesting that the former culture was more homogenous at the onset of continuous medium flow than the latter. Similarly, a long first interval before the first (adaptive) peak of cycloheximide-resistant macroconidia was observed in both A24-S fermentations.…”

“…Fluctuations in the concentration of cycloheximideresistant macroconidia were monitored during the first A24-S experiment and seven peaks of cycloheximide were observed (data not shown). After the first interval, which lasted about 336 h or 87 generations, the average interval between peaks in the concentration of cycloheximide-resistant macroconidia was 208 f 28 h or about 54 generations, and was significantly ( P < 0.05, t-test) longer than the intervals observed for either the A3/5 (Wiebe et a/., 1993) or the A23-S chemostat populations (124 f 12 h and 160 f 12 h, respectively).…”