Biomedical Engineering Reference
In-Depth Information
11.2.2.3
Research Methods for the Relationships
of the Cellulose-Degrading Microorganism Community [
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36
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Microbial ecology studies often take macromolecules, such as fatty acids, nucleic
acids, proteins, and metabolites, related to microbes as life markers. These markers
contain much information to reflect the characteristics of microbial populations from
different aspects.
(1) Phospholipid Fatty Acids
Phospholipid fatty acids (PLFAs) are the cell membrane constant component
of living microorganisms. So, they are sensitive to environmental factors and
significantly different among species. The PLFA number and type and the ratio
between different fatty acids may reflect the in situ microbial community structure
and vitality in soil. PLFAs with different chemical structures characterize different
microorganisms. Mcmahon analyzed PLFA labeled with stable
13
C and found that
the content of 18:2
6 fatty acids was high in the process of ryegrass degradation
in soil, which revealed that fungi played a major role in the ryegrass degradation
process. PLFAs can only provide a rough generalization for microbial populations.
Other methods should be applied for the analysis of microbial systems.
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(2) Ribosomal RNA
Ribosomal RNA is conserved in evolution. Not only a conserved region but also
some variation districts are contained in rRNA, which provides the foundation for
positioning and analysis of the genetic relationship for a system. It is fairly common
to analyze system characteristics of microorganisms such as bacteria, archaea, and
fungi by 16S rRNA and 18S rRNA as molecular markers. The rRNA database
continues to be supplemented and improved, and many ribosomal sequence analyses
from microorganisms are related to cellulose degradation. Conserved primers
could be designed by finding microorganisms with similar genetic relationship
characteristics in the system. Then, a nucleic acid sequence could be amplified by
PCR to study corresponding microorganisms. The composition of the cellulose-
degrading bacteria in soil was analyzed by amplifying with specific primers from
Clostridium
genus degrading cellulose.
(3) Functional gene research methods
Cellulase is a critical functional protein for cellulose-degrading microbes to degrade
cellulosic biomass. According to the cellulase gene as a reference sequence,
primers can be designed to investigate the distribution of cellulose degradation
microorganisms and their phylogenetic relationship. This way, actual functional
characteristics could be better reflected because a functional protein enzyme is
involved. Starting from a functional gene is more targeted and clear. Jacobsen used
cellulase functional gene primers to amplify and analyze cellulase gene diversity
and designed gene-specific primers for the cellulose exoglucosidase 7 family, as
well as for the endoglucosidase of family 45. The results showed that cornstalk
