U.S. Salinity Lab, ARS, USDA, Riverside, California, USA.
U.S. Salinity Lab, ARS, USDA, Riverside, California, USA
Appl Environ Microbiol. 2020 Aug 18;86(17). doi: 10.1128/AEM.00948-20.
Many studies have examined the role that conjugation plays in disseminating antibiotic resistance genes in bacteria. However, relatively little research has quantitively examined and modeled the dynamics of conjugation under growing and nongrowing conditions beyond a couple of hours. We therefore examined growing and nongrowing cultures of over a 24-h period to understand the dynamics of bacterial conjugation in the presence and absence of antibiotics with pUUH239.2, an IncFII plasmid containing multiantibiotic- and metal-resistant genes. Our data indicate that conjugation occurs after cells divide and before they have transitioned to a nongrowing phase. The result is that there is only a small window of opportunity for to conjugate with pUUH239.2 under both growing and nongrowing conditions. Only a very small percentage of the donor cells likely are capable of even undergoing conjugation, and not all transconjugants can become donor cells due to molecular regulatory controls and not being in the correct growth phase. Once a growing culture enters stationary phase, the number of capable donor cells decreases rapidly and conjugation slows to produce a plateau. Published models did not provide accurate descriptions of conjugation under nongrowing conditions. We present here a modified modeling approach that accurately describes observed conjugation behavior under growing and nongrowing conditions. There has been growing interest in horizontal gene transfer of antibiotic resistance plasmids as the antibiotic resistance crisis has worsened over the years. Most studies examining conjugation of bacterial plasmids focus on growing cultures of bacteria for short periods, but in the environment, most bacteria grow episodically and at much lower rates than in the laboratory. We examined conjugation of an IncFII antibiotic resistance plasmid in under growing and nongrowing conditions to understand the dynamics of conjugation under which the plasmid is transferred. We found that conjugation occurs in a narrow time frame when is transitioning from a growing to nongrowing phase and that the conjugation plateau develops because of a lack of capable donor cells in growing cultures. From an environmental aspect, our results suggest that episodic growth in nutrient-depleted environments could result in more conjugation than sustained growth in a nutrient rich environment.
许多研究都考察了接合在细菌中传播抗生素抗性基因的作用。然而，在超过几个小时的时间内，定量研究和模拟生长和非生长条件下的接合动态的研究相对较少。因此，我们在 24 小时内检查了生长和非生长的 培养物，以了解在存在和不存在抗生素的情况下，带有 pUUH239.2 的细菌接合的动态，pUUH239.2 是一种含有多抗生素和金属抗性基因的 IncFII 质粒。我们的数据表明，接合发生在 细胞分裂后，并且在它们过渡到非生长阶段之前。结果是，在生长和非生长条件下， 与 pUUH239.2 接合的机会窗口非常小。只有极少数供体细胞有可能进行接合，并且由于分子调控控制和不在正确的生长阶段，并非所有的转导子都能成为供体细胞。一旦生长培养物进入静止期，有能力的供体细胞数量迅速减少，接合速度减慢，达到平台期。已发表的模型不能准确描述非生长条件下的接合。我们在这里提出了一种改进的建模方法，可以准确描述生长和非生长条件下观察到的接合行为。随着多年来抗生素耐药性危机的加剧，人们对水平基因转移抗生素抗性质粒越来越感兴趣。大多数研究都集中在短时间内检查细菌质粒的接合，但在环境中，大多数细菌间歇性生长，生长速度比实验室中慢得多。我们检查了在生长和非生长条件下 中 IncFII 抗生素抗性质粒的接合，以了解质粒转移时的接合动态。我们发现，当 从生长阶段向非生长阶段过渡时，接合发生在一个狭窄的时间框架内，并且由于生长培养物中缺乏有能力的供体细胞，接合平台期发展。从环境方面来看，我们的结果表明，在营养匮乏的环境中间歇性生长可能会导致比在营养丰富的环境中持续生长更多的接合。
