The Chitin Catabolic Cascade in the Marine Bacterium Vibrio Furnissii. Characterization of an N,N'-diacetyl-chitobiose Transport System

The disaccharide N,N'-diacetyl-chitobiose, (GlcNAc)2, is critical in chitin dissimilation by Vibrio furnissii and, as reported here, is taken up by a specific permease. Since (GlcNAc)2 is rapidly catabolized by V. furnissii, a non-hydrolyzable thioglycoside analogue was used: methyl beta-N,N'-[3H]diacetyl-thiochitobioside (Me-[3H]TCB). Me-TCB and TCB substitute for (GlcNAc)2 as chemoattractants and inducers of beta-N-acetylglucosaminidase activity. The [3H]Me-TCB uptake system was induced only by (GlcNAc)2 and by (GlcNAc)n that can be converted to (GlcNAc)2. The Km for [3H]Me-TCB uptake was </=1 microM and was not affected by Na+ or K+. Uptake appeared to be unidirectional, and in 0.4 M sucrose (+/- K+) the cells accumulated [3H]Me-TCB until it was depleted from the medium, giving an internal concentration of 0.1 M and an internal/external ratio > 1,000. The only effective inhibitors of uptake were: (GlcNAc)n, n = 2-4 > cellobiose > (GlcNAc)5. In 50% artificial sea water (or sucrose/Na+), [3H]Me-TCB accumulation attained a constant steady state level because of efflux, a Na+-dependent process. The physiological implications of these results are considered.