Toratani Tadayuki, Shoji Toshihiro, Ikehara Tomonori, Suzuki Kazushi, Watanabe Takeshi
Department of Applied Biological Chemistry, Faculty of Agriculture, Niigata University, 8050 Ikarashi-2, Niigata 950-2181, Japan.
Microbiology (Reading). 2008 May;154(Pt 5):1326-1332. doi: 10.1099/mic.0.2007/016246-0.
N,N'-diacetylchitobiose [(GlcNAc)(2)] is the main degradation product from chitin by the action of chitinases of Serratia marcescens 2170. Uptake of (GlcNAc)(2) via a (GlcNAc)(2)-specific enzyme II permease by this bacterium has been demonstrated previously. Here, we report the contribution of chitobiase and N-acetylglucosamine (GlcNAc) uptake to the utilization of (GlcNAc)(2). When S. marcescens 2170 was cultivated in a medium containing chitin, chitobiase activity was detected both inside and outside the cells; intracellular chitobiase was more abundant and suggested to be mainly located in the periplasm. Production of chitobiase was induced by GlcNAc and more effectively by (GlcNAc)(2). For induction of chitobiase, uptake of (GlcNAc)(2) was essential but ChiR, an essential regulator of chitinase induction, was not required. S. marcescens 2170 grew well on both GlcNAc and (GlcNAc)(2) but mutants defective in either chitobiase or NagE, the GlcNAc-specific enzyme II permease, showed reduced growth on (GlcNAc)(2). These results suggest that, in addition to uptake as (GlcNAc)(2), a proportion of the (GlcNAc)(2) is converted to GlcNAc by chitobiase, mainly in the periplasm, and incorporated into the cytoplasm by NagE. The mutant defective in chitobiase grew more slowly on (GlcNAc)(2) than on GlcNAc, indicating that (GlcNAc)(2) is less efficiently fermented by S. marcescens 2170 in the absence of chitobiase. Therefore, uptake as both (GlcNAc)(2) and GlcNAc is important for efficient utilization of (GlcNAc)(2) in S. marcescens.
N,N'-二乙酰壳二糖[（GlcNAc）₂]是粘质沙雷氏菌2170的几丁质酶作用于几丁质产生的主要降解产物。此前已证明该细菌通过一种（GlcNAc）₂特异性的酶II通透酶摄取（GlcNAc）₂。在此，我们报告了壳二糖酶和N - 乙酰葡糖胺（GlcNAc）摄取对（GlcNAc）₂利用的贡献。当粘质沙雷氏菌2170在含有几丁质的培养基中培养时，在细胞内外均检测到壳二糖酶活性；细胞内壳二糖酶含量更高，提示其主要位于周质空间。壳二糖酶的产生由GlcNAc诱导，而由（GlcNAc）₂诱导更有效。对于壳二糖酶的诱导，（GlcNAc）₂的摄取是必需的，但几丁质酶诱导的必需调节因子ChiR并非必需。粘质沙雷氏菌2170在GlcNAc和（GlcNAc）₂上均生长良好，但壳二糖酶或NagE（GlcNAc特异性的酶II通透酶）缺陷的突变体在（GlcNAc）₂上的生长表现出下降。这些结果表明，除了以（GlcNAc）₂形式摄取外，一部分（GlcNAc）₂主要在周质空间被壳二糖酶转化为GlcNAc，并通过NagE转运到细胞质中。壳二糖酶缺陷的突变体在（GlcNAc）₂上的生长比在GlcNAc上更缓慢，表明在没有壳二糖酶的情况下，粘质沙雷氏菌2170对（GlcNAc）₂的发酵效率较低。因此，以（GlcNAc）₂和GlcNAc两种形式摄取对于粘质沙雷氏菌有效利用（GlcNAc）₂很重要。
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