Chitin degradation by Clostridium sp. strain 9.1 in mixed cultures with saccharolytic and sulfate‐reducing bacteria

The fermentation of chitin was studied in pure and cocultures of the chitinolytic Clostridium strain 9.1 and various non‐hydrolytic sugar‐fermenting and sulfate‐reducing bacteria. A 5‐ to 8‐fold enhancement of the rate of chitin degradation was observed, which was not due to the alleviation of inhibition of the chitinolytic enzyme system by polymer hydrolysis products. This was concluded from the observation that rates of chitinolysis and fermentation were unaffected by the addition of N ‐acetylglucosamine (NAG) or NAG‐oligomers to pure cultures of strain 9.1, and from the absence of an unequivocal relation between the ability of a secondary bacterium to consume potentially inhibitory hydrolysis products and its capacity to stimulate chitin degradation. The acceleration of chitin fermentation in the presence of sugar‐fermenting bacteria was the result of a release by these secondary populations of growth factors essential to strain 9.1. These factors comprised a high molecular, thioredoxin‐like compound responsible for enhanced chitinolytic activity [10], and various low molecular compounds necessary for optimal growth. The sulfate reducers (except Desulfovibrio sp. strain 20028) released primarily the high molecular growth factor in coculture with strain 9.1. NAG‐fermenting bacteria consumed approximately 10% of the hydrolysis products, whereas species capable of utilizing both mono‐ and oligomeric sugars fermented at least 50% of the sugars produced by strain 9.1. Nevertheless, the rate of chitinolysis in these cocultures proceeded at very similar rates. The observed interactions between Clostridium sp. strain 9.1 and the secondary populations are discussed in relation to the results from studies on mixed culture fermentations of cellulosic substrates reported in the literature.