Pieterse Bart, Leer Rob J, Schuren Frank H J, van der Werf Mariët J
TNO Quality of Life, Utrechtseweg 48, 3700 AJ Zeist, The Netherlands.
Wageningen Centre for Food Sciences, Diedenweg 20, 6700 AN, Wageningen, The Netherlands.
Microbiology (Reading). 2005 Dec;151(Pt 12):3881-3894. doi: 10.1099/mic.0.28304-0.
The organic acid lactate is the predominant fermentation product of Lactobacillus plantarum. The undissociated form of this organic acid is a strong growth inhibitor for the organism. Different theories have been postulated to explain the inhibitory effects of lactic acid: (i) toxicity arising from the dissipation of the membrane potential, (ii) acidification of the cytosol, or (iii) intracellular anion accumulation. In general, organic acid stresses are complex to study, since their toxicity is highly dependent on their degree of dissociation and thus on the pH. In this study, transcription profiles of L. plantarum grown in steady-state cultures that varied in lactate/lactic acid concentration, pH, osmolarity and absolute and relative growth rate, were compared by microarray analysis. By doing so, the differential expression of multiple groups of genes could specifically be attributed to the different aspects of lactic acid stress. A highly coherent group of lactic acid-responsive, cell surface protein-encoding genes was identified, to which no function has previously been assigned. Moreover, a group of genes that showed increased expression in response to the combination of lactic acid and a lower growth rate is expected to be involved in the formation of the alternative fermentation end-products malate, acetate and ethanol. One of these pathways is the phosphoketolase by-pass that is typical for bifidobacteria.
有机酸乳酸是植物乳杆菌的主要发酵产物。这种有机酸的未解离形式是该生物体的一种强效生长抑制剂。人们提出了不同的理论来解释乳酸的抑制作用：（i）膜电位耗散引起的毒性，（ii）细胞质酸化，或（iii）细胞内阴离子积累。一般来说，有机酸胁迫很难研究，因为它们的毒性高度依赖于它们的解离程度，进而依赖于pH值。在本研究中，通过微阵列分析比较了在乳酸/乳酸浓度、pH值、渗透压以及绝对和相对生长速率不同的稳态培养物中生长的植物乳杆菌的转录谱。通过这样做，多组基因的差异表达可以具体归因于乳酸胁迫的不同方面。鉴定出了一组高度相关的乳酸反应性、编码细胞表面蛋白的基因，此前尚未赋予其任何功能。此外，一组在乳酸和较低生长速率共同作用下表达增加的基因预计参与替代发酵终产物苹果酸、乙酸和乙醇的形成。这些途径之一是双歧杆菌特有的磷酸酮醇酶旁路。
