Summary. Clostridium thermocellum is well known for its ability to convert cellulose into ethanol and to hydrolyse hemicellulose. The present work shows its ability to hydrolyse model pectins and to use them for growth. The main products on these substrates as well as on sugar beet pulps were as follows: acetate, ethanol and methanol. Galacturonase and lyase activities were measured in the fermentation broths. As shown by the accumulation of methanol in the "medium, there is a pectin esterase activity but this one seems to be very low.

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SummaryA general model of the kinetics of microbial growth has been developed involving the kinet.ics of incorporat,ion of srtbstrat,e into biomass and t.he maintenance energy requiremetit,s.Results obt.ained from bat.ch cultures of the yeast Saccharo7tiyces cerevisiae growing in synthetic media at. pH 5.1 and 30°C permitted all biological parameters in the model to be calciilated.Values obtained for these pat ameters were: maximiim specific glricose ript8ake rate (ps,,,), 2.08 g/g biomassihr; apparent llichaelis constant, for glucose ( K s ) , . hlass balances for aerobic and anaerobic cnlt*iires confirmed the results obtained from the generalized model. Iles\ilts presented suggested Lhe operation of a mechanism for regulating energy-yielding met abolisni which illvolved an eqriilibrinm between the systems of oxidative phosphorylation and dephosphorylat,ion and was dependent iipon the level of cat abolite repression.

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