The chitin catabolic cascade in the marine bacterium Vibrio furnissii - Characterization of an N,N'-diacetyl-chitobiose transport system

The disaccharideN,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'-[H-3]diacetyl-thiochitobioside (Me-[H-3]TCB). Me-TCB and TCB substitute for (GlcNAc)(2) as chemoattractants and inducers of beta-N-acetylglucosaminidase activity. The [H-3]Me-TCB uptake system was induced only by (GlcNAc)(2) and by (GlcNAc)(n) that can be converted to (GlcNAc)(2). The K-m for [H-3]Me-TCB uptake was less than or equal to 1 mu M and was not affected by Na+ or K+, Uptake appeared to be unidirectional, and in 0.4 M sucrose (+/- K+) the cells accumulated [H-3]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+), [H-3]Me-TCB accumulation attained a constant steady state level because of efflux, a Na+-dependent process. The physiological implications of these results are considered.