Vadyvaloo Viveka, Snoep Jacky L, Hastings John W, Rautenbach Marina
Department of Biochemistry, University of Stellenbosch, Private Bag X1, 7602 Matieland, South Africa.
Microbiology (Reading). 2004 Feb;150(Pt 2):335-340. doi: 10.1099/mic.0.26731-0.
High-level resistance to class IIa bacteriocins has been directly associated with the absent EIIAB(Man) (MptA) subunit of the mannose-specific phosphoenolpyruvate-dependent phosphotransferase system (PTS) (EIIt(MAN)) in Listeria monocytogenes strains. Class IIa bacteriocin-resistant strains used in this study were a spontaneous resistant, L. monocytogenes B73-MR1, and a defined mutant, L. monocytogenes EGDe-mptA. Both strains were previously reported to have the EIIAB(Man) PTS component missing. This study shows that these class IIa bacteriocin-resistant strains have significantly decreased specific growth and glucose consumption rates, but they also have a significantly higher growth yield than their corresponding wild-type strains, L. monocytogenes B73 and L. monocytogenes EGDe, respectively. In the presence of glucose, the strains showed a shift from a predominantly lactic-acid to a mixed-acid fermentation. It is here proposed that elimination of the EIIAB(Man) in the resistant strains has caused a reduced glucose consumption rate and a reduced specific growth rate. The lower glucose consumption rate can be correlated to a shift in metabolism to a more efficient pathway with respect to ATP production per glucose, leading to a higher biomass yield. Thus, the cost involved in obtaining bacteriocin resistance, i.e. losing substrate transport capacity leading to a lower growth rate, is compensated for by a higher biomass yield.
对IIa类细菌素的高水平抗性已直接与单核细胞增生李斯特菌菌株中甘露糖特异性磷酸烯醇丙酮酸依赖性磷酸转移酶系统（PTS）（EIIt（MAN））缺失的EIIAB（Man）（MptA）亚基相关。本研究中使用的IIa类细菌素抗性菌株包括一株自发抗性菌株——单核细胞增生李斯特菌B73-MR1，以及一株特定突变体——单核细胞增生李斯特菌EGDe-mptA。先前报道这两种菌株均缺失EIIAB（Man）PTS组分。本研究表明，这些IIa类细菌素抗性菌株的比生长速率和葡萄糖消耗速率显著降低，但它们的生长产量也分别比其相应的野生型菌株——单核细胞增生李斯特菌B73和单核细胞增生李斯特菌EGDe高得多。在有葡萄糖存在的情况下，这些菌株显示出从主要的乳酸发酵向混合酸发酵的转变。本文提出，抗性菌株中EIIAB（Man）的缺失导致葡萄糖消耗速率降低和比生长速率降低。较低的葡萄糖消耗速率可能与代谢转变为关于每葡萄糖产生ATP更有效的途径相关，从而导致更高的生物量产量。因此，获得细菌素抗性所涉及的代价，即失去底物转运能力导致生长速率降低，被更高的生物量产量所补偿。
