Civil Engineering Reference
In-Depth Information
precursor) in the cytoplasmic membrane, and is extruded from the pores as micro-
i brils of approximately 1.5 nm in width [15]. h e microi brils aggregate into ribbon-
shaped i brils approximately 40 nm in width [31].
Bacterial cellulose forms as a thick mat, called a pellicle, at the air/surface interface
when grown statically in liquid culture (Figure 4.2) [32, 33]. h e pellicle is composed
of randomly associated i brils from the cells in the culture [15]. It is believed that cel-
lulose production is roughly proportional to cell growth. However, when cultures are
agitated and aerated, cell growth increases and cellulose production decreases. It has
also been found that shaken and agitated cultures result in macroscopic changes to
the cellulose. Rather than forming as a smooth pellicle on the surface of the culture,
the cellulose can accumulate as spherical pellets (Figure 4.3) [32, 34]. Microscopic dif-
ferences in the cellulose also occur depending on the culture conditions, as described
below. It is likely that the increased exposure to oxygen under agitated conditions
Figure 4.2
Bacterial cellulose pellicle grown across the top of liquid culture. Reproduced from [33] with
permission from Wiley.
Figure 4.3
Bacterial cellulose pellets grown in agitated culture. Reproduced from [34] with permission
from Springer. Scale bar is 5 mm.
