ABSTRACT
FRED J . STUTZENBERGER Clemson U n ivers ity , Clemson, Sou th Carolina
I. INTRODUCTION
Cellulose is th e w orld’s most ab u n d an t o rgan ic m aterial (1 ) . T h e re fo re , enzym atic deg rad a tio n of th is polym er is c ruc ia l to th e cycling of ca rbon within bo th th e marine and te r r e s tr ia l h a b ita ts . M icroor ganism s (bo th aerobic species su ch as tho se found in w ell-aerated soils and com posts, and anaerobes su ch as tho se active in th e h e r b ivo re rum en) a re respo n sib le fo r most o f th e cellulose carbon r e cycling (2 ) . A lthough th e ecological im portance of cellulose decom position has long been reco g n ized , most of th e re c e n t in te re s t in cellulolytic system s h as been stim ulated b y th e p ro sp e c ts fo r com mercial u tilization of cellu lases in b ioconversion p ro c e sse s . The ma jo rity of th ese s tu d ie s on cellu lase b io sy n th es is and ac tiv ity have dealt w ith th e mesophilic fu n g i, o f which Trichoderm a reese i h as been th e c e n te r of a tten tio n (rev iew ed in R ef. 3 ). H ow ever, a s e rious lim itation env isioned in th e la rg e -sca le application o f m esophil ic fungal cellu lases in biom ass conversion may be th e ir re la tiv e ly poor tem p era tu re s tab ility u n d e r u sage and recy c lin g conditions ( 4 ,5 ) . The ad v an tag es o f u s in g therm ophiles fo r cellu lase p ro d u c tion (rev iew ed in R ef. 6 ) can be b rie fly lis ted as follows: (1) lower cooling co s ts in la rg e -sca le c u ltu re s ; ( 2 ) in c reased mass tr a n s fe r due to dec reased fluid v iscosity a t h ig h e r te m p e ra tu re s ; (3) red u ced r isk of contam ination; (4) enhanced volitalization o f p ro d u c ts ( e . g . ,
ethano l) at h ig h e r te m p e ra tu re s ; (5) nonpathogen ic ity of therm o p h ile s , which in most cases cannot grow at 37°C; and ( 6 ) a le s se r d eg ree of enzyme inactivation d u rin g re c o v e ry , m anipulation, and s to rag e of enzym es. D isadvan tages inc lude: (1) g re a te r s tr e s s on bio technology hardw are such as con tro l se n so rs ; ( 2 ) excessive ev a p ora tion (may be advan tageous for co n cen tra tion o f p ro d u c ts ) ; (3) lower to lerance to p ro d u c ts such as alcohol; and (4) d ecreased o x y gen so lubility a t h igh te m p e ra tu re s . T h is la s t po in t is of p a r tic u la r significance for th e ob ligately aerobic therm ophiles, since oxygen so lub ility at 50°C is only about th re e - fo u r th s th a t a t room tem pera tu re ( 7 ).
