Molecular and biochemical analysis of the galactose phenotype of dairy Streptococcus thermophilus strains reveals four different fermentation profiles
Molecular and biochemical analysis of the galactose phenotype of dairy Streptococcus thermophilus strains reveals four different fermentation profiles
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DOI：
10.1128/aem.71.7.3659-3667.2005
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发表时间：
2005-07-01
影响因子：
4.4
通讯作者：
De Vuyst, L
中科院分区：
文献类型：
--
作者：
de Vin, F;Rådström, P;De Vuyst, L
乳糖限制发酵的49个乳制品嗜热链球菌菌株显示四个不同的发酵曲线相对于乳糖消耗后的乳糖耗尽。所有菌株在乳糖上生长期间将半乳糖分泌到培养基中，除了菌株IMDOST 40，其也显示极高的半乳糖激酶（GalK）活性。在该菌株中发现了8个半乳糖阳性表型，并测定了它们的发酵特性和Leloir酶活性。由于gal启动子似乎在半乳糖表型中起重要作用，因此对所有菌株的galR-galK基因间区域进行测序，得到8个不同的核苷酸序列（NS 1至NS 8）。Gal启动子在Gal阳性表型中起重要作用，但并不完全决定它。虽然GalT和GalE活性检测到所有的Gal阳性菌株，GalK活性只能检测到两个八个Gal阳性菌株。这一发现表明，其他六个S。嗜热菌菌株通过另一途径代谢半乳糖。对于获得的每种类型的发酵谱，选择代表性菌株并对四个完整的Leloir基因簇进行测序。事实证明，Gal阳性菌株比Gal阴性菌株在其Gal基因中包含更多的氨基酸差异。最后，研究了不同乳杆菌对乳糖-半乳糖利用的多样性。本研究所用的嗜热菌菌株经RAPD-PCR鉴定。5株在galR-galK基因间隔区含有NS 2核苷酸序列的Gal阳性菌株亲缘关系较近。
Lactose-limited fermentations of 49 dairy Streptococcus thermophilus strains revealed four distinct fermentation profiles with respect to galactose consumption after lactose depletion. All the strains excreted galactose into the medium during growth on lactose, except for strain IMDOST40, which also displayed extremely high galactokinase (GalK) activity. Among this strain collection eight galactose-positive phenotypes sensu stricto were found and their fermentation characteristics and Leloir enzyme activities were measured. As the gal promoter seems to play an important role in the galactose phenotype, the galR-galK intergenic region was sequenced for all strains yielding eight different nucleotide sequences (NS1 to NS8). The gal promoter played an important role in the Gal-positive phenotype but did not determine it exclusively. Although GalT and GalE activities were detected for all Gal-positive strains, GalK activity could only be detected for two out of eight Gal-positive strains. This finding suggests that the other six S. thermophilus strains metabolize galactose via an alternative route. For each type of fermentation profile obtained, a representative strain was chosen and four complete Leloir gene clusters were sequenced. It turned out that Gal-positive strains contained more amino acid differences within their gal genes than Gal-negative strains. Finally, the biodiversity regarding lactose-galactose utilization among the different S. thermophilus strains used in this study was shown by RAPD-PCR. Five Gal-positive strains that contain nucleotide sequence NS2 in their galR-galK intergenic region were closely related.