Our results, obtained from shaken and agitated cultures
at high glucose concentrations, differed from those
described above. A. xylinum BRCS preferentially
metabolized glucose to gluconic acid during the lag and
initial growth phase, and cellulose was not produced during
these periods. After glucose was almost completely
consumed, cellulose began to be produced from the gluconic
acid accumulated, and was accompanied by cell
growth. Masaoka et al. (5) studied cellulose production
by A. xylinum IF0 13693. They reported that the yield
of cellulose, relative to the glucose consumed, decreased
with an increase in initial glucose concentration, and the
accumulated gluconic acid did not affect cellulose production.
Schramm et al. (12) also reported that A. xyiinum
oxidized a portion of glucose to gluconic acid, with
the accumulated gluconic acid lowering the pH of the
culture medium and inhibiting cellulose production.
The fermentation profile in a jar fermentor (Fig. 5)
was similar to that in a shaking flask culture (Fig. 1).
However, cell concentration in a jar fermentor was
much higher than that in a flask culture. This result was
probably due to the instability of A. xylinum, which may have resulted in CelP mutants under agitated conditions.
As described previously, Gel- mutants did not
appear at low shaking speed in this study. This result
suggests that low shear stress is not detrimental to the cellulose
production by strain BRCS; but in agitated culture
conditions, the appearance of non-producers apparently
occurred at a high frequency which was enough to shift
the population balance of a culture from celluloseproducing
to cellulose non-producing types during
growth. Gel- mutants were estimated to comprise over
50% of the cell population at the stationary phase in
fermentor cultures (data not shown). Cel- mutants in cultivation
were measured using the Valla and Kjosbakken
(4) method. Growth of mixed cultures of cellulose
producing and non-producing strains in agitated cultures
strongly favored Gel- mutants due to selective aggregation
of Gel+ cells, which results in the limitation of mass
transfer with respect to oxygen. This resulted in loss of
the ability to produce cellulose and the gradual overtaking
of Gel+ by Gel-.