Phenotypic Diversity Caused by Differential RpoS Activity among Environmental Escherichia coli Isolates
Phenotypic Diversity Caused by Differential RpoS Activity among Environmental Escherichia coli Isolates
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DOI：
10.1128/aem.05274-11
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发表时间：
2011-11-01
影响因子：
4.4
通讯作者：
Schellhorn, Herb E.
中科院分区：
文献类型：
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作者：
Chiang, Sarah M.;Dong, Tao;Schellhorn, Herb E.
由动物宿主沉积到环境中的肠道细菌受到不同的选择压力。这些压力可能作用于细菌群体的表型差异，并选择适应性突变以在压力中生存。作为研究环境细菌表型多样性的模型，我们研究了环境大肠杆菌分离株中应激反应σ因子RpoS的突变。通过检查琥珀酸和过氧化氢酶活性（两种RpoS依赖表型）的生长，对来自安大略（加拿大）城市海滩和附近粪便污染源的共2,040株RpoS功能进行了筛选。确定了45个分离株的rpoS序列，包括所有候选RpoS突变体，其中6个分离株被确认为RpoS功能完全丧失的突变体。与实验室菌株相似，这些环境分离株的RpoS表达是稳定期依赖性的。然而，RpoS调节子成员KatE和AppA的表达与实验室菌株相比，在几种环境分离株中的表达水平不同。此外，将rpoS（+）菌株接种于琥珀酸盐培养基上，可以从环境E.杆菌自然分离和琥珀酸选择的RpoS突变体在贫碳源上的世代时间较短，并且比其rpoS（+）等基因亲本菌株具有较低的抗逆性。这些结果表明，RpoS突变体存在于环境中（在分离株中的频率为0.003），并且与实验室和致病菌株类似，在贫碳源上生长选择环境E中的rpoS突变。杆菌RpoS选择可能是表型多样化的重要决定因素，因此，E。环境中的大肠杆菌。
Enteric bacteria deposited into the environment by animal hosts are subject to diverse selective pressures. These pressures may act on phenotypic differences in bacterial populations and select adaptive mutations for survival in stress. As a model to study phenotypic diversity in environmental bacteria, we examined mutations of the stress response sigma factor, RpoS, in environmental Escherichia coli isolates. A total of 2,040 isolates from urban beaches and nearby fecal pollution sources on Lake Ontario (Canada) were screened for RpoS function by examining growth on succinate and catalase activity, two RpoS-dependent phenotypes. The rpoS sequence was determined for 45 isolates, including all candidate RpoS mutants, and of these, six isolates were confirmed as mutants with the complete loss of RpoS function. Similarly to laboratory strains, the RpoS expression of these environmental isolates was stationary phase dependent. However, the expression of RpoS regulon members KatE and AppA had differing levels of expression in several environmental isolates compared to those in laboratory strains. Furthermore, after plating rpoS(+) isolates on succinate, RpoS mutants could be readily selected from environmental E. coli. Naturally isolated and succinate-selected RpoS mutants had lower generation times on poor carbon sources and lower stress resistance than their rpoS(+) isogenic parental strains. These results show that RpoS mutants are present in the environment (with a frequency of 0.003 among isolates) and that, similarly to laboratory and pathogenic strains, growth on poor carbon sources selects for rpoS mutations in environmental E. coli. RpoS selection may be an important determinant of phenotypic diversification and, hence, the survival of E. coli in the environment.