Cellodextrin utilization by Bifidobacterium breve UCC2003. Bifidobacterium breve UCC2003

The transcription of the cldEFGC gene cluster of Bifidobacterium breve UCC2003 was shown to be induced upon growth on cellodextrins, implicating these genes in the metabolism of these sugars. Phenotypic analysis of a B. breve UCC2003::cldE insertion mutant confirmed that the cld gene cluster is exclusively required for cellodextrin utilization by this bacterium. HPAEC-PAD analysis of medium samples obtained during growth of B. breve UCC2003 on a mixture of cellodextrins revealed its ability to utilize cellobiose, cellotriose, cellotetraose and cellopentaose, with cellotriose representing the preferred substrate. The cldC gene of the cld operon of B. breve UCC2003 was shown to be the first described bifidobacterial β-glucosidase exhibiting hydrolytic activity towards various cellodextrins. Overall design: In order to investigate differences in gene expression patterns of B. breve UCC2003 when grown on cellobiose or cellodextrins as compared to growth on glucose, DNA microarray experiments were performed. Total RNA was isolated from B. breve UCC2003 cultures grown on cellobiose, cellodextrins, or glucose (see Materials and Methods). The cultures were harvested at the time points that ensured that B. breve UCC2003 was metabolizing cellobiose or cellodextrins as opposed to the residual glucose present in the cellodextrin preparation. Analysis of the DNA microarray data was obtained from two independent biological replicates.

研究显示，短双歧杆菌（Bifidobacterium breve）UCC2003的cldEFGC基因簇（cldEFGC gene cluster）在以纤维糊精（cellodextrins）为碳源生长时会被诱导转录，提示该基因簇参与了这类糖类的代谢过程。对一株短双歧杆菌UCC2003::cldE插入突变体的表型分析（phenotypic analysis）证实，该cld基因簇是该菌株利用纤维糊精的唯一必需基因簇。采用高效阴离子交换色谱-脉冲安培检测（HPAEC-PAD）对短双歧杆菌UCC2003在纤维糊精混合物中生长的培养基样本进行分析，结果表明该菌株可利用纤维二糖（cellobiose）、纤维三糖（cellotriose）、纤维四糖（cellotetraose）及纤维五糖（cellopentaose），其中纤维三糖为其优先利用的底物。短双歧杆菌UCC2003的cld操纵子（cld operon）中的cldC基因，是首个被报道的双歧杆菌来源的β-葡萄糖苷酶（β-glucosidase），可对多种纤维糊精展现水解活性。
实验设计概况：为探究短双歧杆菌UCC2003分别以纤维二糖、纤维糊精为碳源生长时，与以葡萄糖为碳源生长的基因表达模式差异，本研究开展了DNA微阵列（DNA microarray）实验。从分别以纤维二糖、纤维糊精或葡萄糖为碳源培养的短双歧杆菌UCC2003菌体中提取总RNA（total RNA），具体操作详见材料与方法（Materials and Methods）。研究人员在确保菌株正代谢纤维二糖或纤维糊精（而非纤维糊精制剂中残留的葡萄糖）的时间点收集培养物。DNA微阵列数据的分析基于两组独立的生物学重复（biological replicates）完成。