ABSTRACT
C o ld -a d a p te d m ic ro o rg a n is m s a re g o o d so u rc e s o f c o ld -a c tiv e e n z y m e s a n d c a n b e c la ssifie d in to tw o m a jo r c la sse s , p s y c h ro p h ile s a n d p s y c h ro tro p h s , o n th e b a s is o f th e ir w a y s o f co ld a d a p ta tio n . A p sy ch ro p h ile is a m ic ro o rg a n is m w ith o p tim a l g ro w th a t 1 5 °C o r lo w er, w h e re a s a p s y c h ro tro p h (o r a lso ca lle d "p s y c h ro to le ra n t" ) is e sse n tia lly a m e so p h ilic m ic ro o rg a n is m th a t c a n a ls o g ro w u n d e r co ld co n d itio n s b e lo w 1 5 °C (M o rita 1 9 7 5 ,1 9 7 6 ) . S u ch lo w te m p e ra tu re co n d itio n s m a y n o t n e c e s s a rily b e "e x tre m e " o n e s for m o s t m icro o rg a n ism s b e ca u s e th ey re m a in v iab le (b u t d o n o t g ro w ) u n d e r s u c h co n d itio n s . N o n e th e le ss , p sy ch ro p h ile s a n d p s y ch ro tro p h s a re r e g a rd e d a s a c la ss o f "e x tre m o p h ile s " d u e to th e ir d is tin ctiv e a b ility to ra p id ly g ro w a t s u ch lo w te m p e ra tu re s . T h e re is p ro b a b ly a c o n tin u ity in th e d is trib u tio n o f o rg a n ism s w h o se h ig h e st g ro w th te m p e ra tu re ra n g e s fro m n e a r 0 ° C to 110 °C , s u ch as p sy ch ro p h ile s , p s y c h ro tro p h s , m e so p h ile s , m o d e ra te th e rm o p h ile s , a n d h y p e rth e rm o p h ile s (A g u ila r 1 9 9 6 , G e rd a y et al. 2 0 0 0 ) .
