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.