ADVANCES IN APPLIED MICROBIOLOGY,
VOLUME 56, 215-261
Extracellular glycosyl hydrolases from clostridia
WOLFGANG
H. SCHWARZ, VLADIMIR V. ZVERLOV AND HUBERT BAHL
Summary
(Concluding Remarks)
Clostridia are
very important organisms for modern biotechnology. In the past, they were used
for the production of acetone and butanol from biomass, and for flax retting
and indigo dyeing. In this article the features of some of the extracellular
enzymes produced by these bacteria to hydrolyze biopolymers are highlighted.
After an introductory overview on the role of anaerobic bacteria and their enzymes
in the digestion of biomass, the unique strategies of the clostridia to cope
with the degradation of insoluble components of biomass, including crystalline cellulose,
hemicellulose, and starch are discussed. This chapter focuses on the modular
structure of these enzymes and the function of non-catalytic modules. The
latter are, e.g., involved in the binding of the substrate or the cell wall.
The last part of this review is a detailed description and comparison of the
different enzyme systems which have been found in clostridia, including
mesophilic and thermophilic species. Some of these enzymes or enzyme systems
are unique among microorganisms and the enormous potential of clostridia as
producers of industrially important enzymes is obvious. In the last decade
significant progress has been achieved in the understanding of the
structure-function relationship of the clostridial type of enzymes and their
modules. The method of enzyme modification by adding modules or the increase in
enzyme activity by complex formation will be a great stimulus for modern
enzymology to customize newly engineered production strains. Thus, it seems to
be possible now to engineer enzymes with optimal features for a given purpose
or even to create a special Clostridium
strain which is able to convert cheap renewable biomass into desired valuable
products. Thus, it is not utopian to believe that, e.g., Clostridium acetobutylicum one day will transform cellulosic wastes
directly to solvents.