Wei Yi, Deikus Gintaras, Powers Benjamin, Shelden Victor, Krulwich Terry A, Bechhofer David H
Department of Pharmacology and Biological Chemistry, Box 1603, Mount Sinai School of Medicine of New York University, New York, NY 10029, USA.
J Bacteriol. 2006 Oct;188(20):7090-100. doi: 10.1128/JB.00885-06.
The growth properties of a new panel of Bacillus subtilis tetL deletion strains and of a derivative set of strains in which tetL is restored to the chromosome support earlier indications that deletion of tetL results in a range of phenotypes that are unrelated to tetracycline resistance. These phenotypes were not reversed by restoration of a tetL gene to its native locus and were hypothesized to result from secondary mutations that arise when multifunctional tetL is deleted. Such genetic changes would temper the alkali sensitivity and Na(+) sensitivity that accompany loss of the monovalent cation/proton activity of TetL. Microarray comparisons of the transcriptomes of wild-type B. subtilis, a tetL deletion strain, and its tetL-restored derivative showed that 37 up-regulated genes and 13 down-regulated genes in the deletion strain did not change back to wild-type expression patterns after tetL was returned to the chromosome. Up-regulation of the citM gene, which encodes a divalent metal ion-coupled citrate transporter, was shown to account for the Co(2+)-sensitive phenotype of tetL mutants. The changes in expression of citM and genes encoding other ion-coupled solute transporters appear to be adaptive to loss of TetL functions in alkali and Na(+) tolerance, because they reduce Na(+)-coupled solute uptake and enhance solute uptake that is coupled to H(+) entry.
一组新的枯草芽孢杆菌tetL缺失菌株以及tetL基因恢复到染色体上的一组衍生菌株的生长特性支持了早期的研究结果，即tetL缺失会导致一系列与四环素抗性无关的表型。这些表型不会因tetL基因恢复到其天然位点而逆转，据推测是由于在多功能tetL缺失时产生的二次突变所致。这种基因变化会缓和伴随TetL单价阳离子/质子活性丧失而出现的碱敏感性和Na(+)敏感性。对野生型枯草芽孢杆菌、tetL缺失菌株及其tetL恢复的衍生物的转录组进行微阵列比较表明，缺失菌株中37个上调基因和13个下调基因在tetL恢复到染色体后并未恢复到野生型表达模式。编码二价金属离子偶联柠檬酸转运蛋白的citM基因的上调被证明是tetL突变体对Co(2+)敏感表型的原因。citM和编码其他离子偶联溶质转运蛋白的基因表达的变化似乎是为了适应TetL在碱耐受性和Na(+)耐受性方面功能的丧失，因为它们减少了Na(+)偶联溶质的摄取，并增强了与H(+)进入偶联的溶质摄取。
