In this step, successive subcultivation under selective enrichment
conditions was used in order to establish the structurally
stable microbial consortium with high cellulose degrading capability.
A number of microbial communities capable of filter paper
degradation with different degradation rates were obtained from
subcultivation of seed cultures from high-temperature sugarcane
bagasse compost under aerobic static conditions. After several
subcultivations, the most active microbial community, designated
MC3F, was capable of extensive filter paper degradation (>50%)
within 7 d at 50◦C. Based on DGGE patterns, the microbial consortium’s
community structure of MC3F tended to stabilize after
successive subcultivations for more than 20 generations (typical
incubation time of 7 d for each batch cycle). In order to assess the
structural stability of the microbial consortium during subcultivation,
the 16S rDNA PCR products amplified from MC3F collected
from different generations were analyzed by denaturing gradient
gel electrophoresis to compare the community DGGE profiles
[6,25]. In overall, similar DGGE patterns among six generations
(between subcultivations 32 and 42) were observed, indicating
structural stability of the composite microbes co-existing in the
consortium, which comprised mainly of approx. 8 major composite
members (Fig. 1). MC3F could be subcultivated for more than 90
generations with high structural and functional stabilities, i.e. >50%
filter paper degradation after the 7-d incubation period in every
generations with no alteration in DGGE patterns (data not shown).
The result thus suggested that MC3F was stable in terms of microbial
community structure and its cellulolytic activity. The microbial
community was tolerant to freezing at -80 ◦C in PCS medium containing
20% glycerol for at least 1 year with no change in microbial
composition as shown by DGGE patterns of the revived community.
This illustrates the high stability of the microbial community
and allows long-term storage of the seed culture for further experimental
studies and application.