Evolution of Bacillus subtilis to Enhanced Growth at Low Pressure: Up-Regulated Transcription of des-desKR, Encoding the Fatty Acid Desaturase System
Evolution of Bacillus subtilis to Enhanced Growth at Low Pressure: Up-Regulated Transcription of des-desKR, Encoding the Fatty Acid Desaturase System
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DOI：
10.1089/ast.2011.0728
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发表时间：
2012-03-01
期刊：
影响因子：
4.2
通讯作者：
Nicholson, Wayne L.
中科院分区：
文献类型：
--
作者：
Fajardo-Cavazos, Patricia;Waters, Samantha M.;Nicholson, Wayne L.
火星上的气压范围为1-10毫巴，约为地球气压的1%（类似于1013毫巴）。低压是火星上陆地微生物的生长抑制因素，并且已经假定了类似于25毫巴的地球细菌生长的假定低压屏障。在先前的通信中，我们描述了枯草芽孢杆菌菌株的分离，该菌株在50毫巴的近抑制性低压下进化出增强的生长能力。为了探索能够使低压适应菌株生长的机制，通过微阵列分析鉴定了在50 mbar下祖先菌株WN 624和低压进化菌株WN 1106之间差异转录的许多基因。在这些基因中有一簇三个候选基因（des、desK和desR），其mRNA水平在WN 1106中高于微阵列上的祖先。通过定量逆转录聚合酶链反应（qRT-PCR）分析证实了这些基因的上调。des、desK和desR基因分别编码Des膜脂肪酸（FA）去饱和酶、DesK传感器激酶和DesR反应调节剂，其功能是在对温度降档的急性反应中维持膜流动性。压力降档仅在WN 1106中引起des mRNA水平的上调，但des-lacZ转录融合体的表达不受影响，这表明des调节对温度与压力降档的响应不同。竞争实验表明，des基因的失活导致轻微的，但统计学上显着的，在50毫巴的菌株WN 1106的健身损失。此外，在1013与50毫巴下生长的细胞的膜FA组合物的分析显示，不饱和脂肪酸与饱和脂肪酸的比率降低，但反异构脂肪酸与异构脂肪酸的比率增加。目前的研究是确定B.枯草芽孢杆菌能够感知并响应新的低压环境胁迫。
The atmospheric pressure on Mars ranges from 1-10 mbar, about 1% of Earth pressure (similar to 1013 mbar). Low pressure is a growth-inhibitory factor for terrestrial microorganisms on Mars, and a putative low-pressure barrier for growth of Earth bacteria of similar to 25 mbar has been postulated. In a previous communication, we described the isolation of a Strain of Bacillus subtilis that had evolved enhanced growth ability at the near-inhibitory low pressure of 50 mbar. To explore mechanisms that enabled growth of the low-pressure-adapted strain, numerous genes differentially transcribed between the ancestor strain WN624 and low-pressure-evolved strain WN1106 at 50 mbar were identified by microarray analysis. Among these was a cluster of three candidate genes (des, desK, and desR), whose mRNA levels in WN1106 were higher than the ancestor on the rnicroarrays. Up-regulation of these genes was confirmed by quantitative reverse transcription polymerase chain reaction (qRT-PCR) analysis. The des, desK, and desR genes encode the Des membrane fatty acid (FA) desaturase, the DesK sensor kinase, and the DesR response regulator, respectively, which function to maintain membrane fluidity in acute response to temperature downshift. Pressure downshift caused an up-regulation of des mRNA levels only in WN1106, but expression of a des-lacZ transcriptional fusion was unaffected, which suggests that des regulation was different in response to temperature versus pressure downshift. Competition experiments showed that inactivation of the des gene caused a slight, but statistically significant, loss of fitness of strain WN1106 at 50 mbar. Further, analysis of membrane FA composition of cells grown at 1013 versus 50 mbar revealed a decrease in the ratio of unsaturated to saturated FAs but an increase in the ratio of anteiso- to iso-FAs. The present study represents a first step toward identification of molecular mechanisms by which B. subtilis could sense and respond to the novel environmental stress of low pressure.