Page 318 - Advances in Textile Biotechnology

Chitin, chitosan and bacterial cellulose for textiles 299

of the long cultivation time and expensive carbon source. To date, fermen-
tation processes using stirred-tanks or airlift reactors have been reported
as the most effective way to produce microbial cellulose on a large scale.
Although agitated culture, where cellulose is synthesized in the form of

fibrous suspensions, pellets or irregular masses (Czaja et al., 2004), causes
some problems such as strain instability, non-Newtonian behavior or proper
oxygen supply (Kouda et al., 1996, 1997a,b), this process has been proposed
as the most suitable technique for economical scale production. One of the
most important problems of agitated culture of bacteria is the generation
of non-producing mutants. The addition of ethanol to the medium has been
found to be effective to repress this spontaneous mutation (Park et al.,
2003). However, to raise a large-scale production, the selection of stable
strains is indispensable (Toyosaki et al., 1995). There have been many studies
on bacterial cellulose production in stirred-tank reactors. Various parame-
ters including reactor design (Kouda et al., 1997b), carbon and nitrogen
sources (Bae and Shoda, 2005a; Naritomi et al., 1998), and pH and dissolved
oxygen (Hwang et al., 1999) have been studied in order to optimize bacte-
rial cellulose production. The addition of water-soluble polysaccharides
such as agar has also been found to enhance the productivity (Bae et al.,
2004). For the optimization of all the experimental parameters that affect
bacterial cellulose production statistical methods have also been described
(Bae and Shoda, 2005b). In addition to bacterial cellulose production in
stirred-tanks, an intensive investigation on production using airlift reactors
has been made in last years. This type of reactor has a low power consump-

tion but requires the supply of oxygen-fortified air to improve the oxygen
transfer in the culture (Chao et al., 2001; Zuo et al., 2006). As for stirred-
tanks, culture conditions, including pH, carbon and nitrogen sources (Noro
et al., 2004), and the presence of water-soluble polysaccharides (Ishida
et al., 2003) have been studied for airlift reactors. The main advantage of
the stirred-tank reactor is its ability to prevent the inhomogeneity of the
culture broth by strong mechanical agitation, whereas the disadvantage is
−1
−1
its high energy cost (0.66 kW h for 1 g L ) for generating the mechanical
−1
power. Conversely, an airlift reactor has a low energy cost (0.11 kW h for
−1
1 g L ) but its agitation power is limited, resulting in low fluidity of the

culture broth, especially at high bacterial cellulose concentrations.
One example of a large-scale production of bacterial cellulose is Cellu-

lon® fibre. This cellulosis fibre, acquired by Monsato (US) in the mid-1990s,
was first developed by two US-based companies, Weyerhaeuser Co. and

Cetus Co. using a deep-tank fermentation technique and a patented, gene-
tically improved Acetobacter strain. The Cellulon® fibres produced by

agitated aerobic bacterial fermentation, are approximately 0.1 μm wide and
of indeterminate length, providing a large surface area.

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