Environmental factors determining the epidemiology and population genetic structure of the Bacillus cereus group in the field.
Environmental factors determining the epidemiology and population genetic structure of the Bacillus cereus group in the field.
复制标题
DOI：
10.1371/journal.ppat.1000905
复制
发表时间：
2010-05-20
期刊：
影响因子：
6.7
通讯作者：
Bonsall MB
中科院分区：
文献类型：
--
作者：
Raymond B;Wyres KL;Sheppard SK;Ellis RJ;Bonsall MB
苏云金芽孢杆菌（Bacillus thuringiensis, Bt）及其杀虫毒素被广泛应用于微生物生物农药和转基因作物中。然而，人们对其种群生物学知之甚少。安全、可持续利用Bt的重要问题包括了解自然选择如何维持杀虫毒素的表达，昆虫致病性Bt在生态上是否与蜡样芽孢杆菌群中的相关人类病原体不同，以及微生物农药的使用如何改变天然细菌种群。为了解决这些问题，我们采用了一种适用于田间试验的MLST方案，其中我们在析因设计中排除/添加了昆虫宿主和微生物农药。昆虫的存在增加了Bt/B的密度。土壤中蜡样菌及表达杀虫毒素菌株的比例。在喷虫和未喷虫的围场中发现了以单一昆虫致病基因型（ST8）为主的接近流行的种群结构。生物杀虫剂ST8在喷洒后在宿主体内增殖，但也发现与任何其他基因型相比，它与叶片的自然关联更大。在一项独立实验中，一些ST8菌株在土壤幼苗的内生和附生定植方面优于一系列非致病性STs。这是Bt作为一种特殊的昆虫病原体在该领域的首次实验证明。这些数据为了解Bt生态和人为因素对Bt种群的影响提供了基础。该Bt自然种群显示出栖息地关联和种群结构，与先前对生态一致性较低的蜡样芽孢杆菌样本收集的MLST研究明显不同。ST8的宿主特异性适应性、与其毒素质粒的密切关联以及在其进化支系中的高流行率与炭疽芽孢杆菌的生物学特性相似。这种流行率还表明，对ST8杀虫毒素的抗性选择将强于对其他毒素类别的抗性选择。苏云金芽孢杆菌是害虫管理中最有用的细菌之一：它被用作环境友好型生物农药，其杀虫毒素被纳入转基因作物中。对其正在进行的经济开发的关注包括昆虫对其毒素的抗性进化的速度，以及苏云金芽孢杆菌在生态和遗传上是否与引起人类和家畜感染的密切相关菌株不同。我们发现土壤和白菜叶上的天然细菌种群由一种昆虫-病原体专门基因型主导，该基因型比其近亲更容易在其宿主可能觅食的叶子上建立种群。喷洒微生物农药和添加昆虫宿主增加了昆虫病原体专家在细菌种群中的比例，证实了这些生物农药的应用是一种安全的昆虫控制手段。苏云金弧菌种群在植物材料上是短暂的，这表明抗性的选择压力也可能是短暂的。然而，在自然群落中占主导地位的基因型在经济上比其他任何基因型都得到了更多的利用，并且在使用苏云金芽孢杆菌进行病虫害防治之前，自然种群中可能已经发生了对该菌株的抗性选择。
Bacillus thuringiensis (Bt) and its insecticidal toxins are widely exploited in microbial biopesticides and genetically modified crops. Its population biology is, however, poorly understood. Important issues for the safe, sustainable exploitation of Bt include understanding how selection maintains expression of insecticidal toxins in nature, whether entomopathogenic Bt is ecologically distinct from related human pathogens in the Bacillus cereus group, and how the use of microbial pesticides alters natural bacterial populations. We addressed these questions with a MLST scheme applied to a field experiment in which we excluded/added insect hosts and microbial pesticides in a factorial design. The presence of insects increased the density of Bt/B. cereus in the soil and the proportion of strains expressing insecticidal toxins. We found a near-epidemic population structure dominated by a single entomopathogenic genotype (ST8) in sprayed and unsprayed enclosures. Biopesticidal ST8 proliferated in hosts after spraying but was also found naturally associated with leaves more than any other genotype. In an independent experiment several ST8 isolates proved better than a range of non-pathogenic STs at endophytic and epiphytic colonization of seedlings from soil. This is the first experimental demonstration of Bt behaving as a specialized insect pathogen in the field. These data provide a basis for understanding both Bt ecology and the influence of anthropogenic factors on Bt populations. This natural population of Bt showed habitat associations and a population structure that differed markedly from previous MLST studies of less ecologically coherent B. cereus sample collections. The host-specific adaptations of ST8, its close association with its toxin plasmid and its high prevalence within its clade are analogous to the biology of Bacillus anthracis. This prevalence also suggests that selection for resistance to the insecticidal toxins of ST8 will have been stronger than for other toxin classes. Bacillus thuringiensis is one of the most useful bacteria in insect pest management: it is used as an environmentally friendly biopesticide and its insecticidal toxins are incorporated into genetically modified crops. Concerns for its ongoing economic exploitation include the rapidity with which insects can evolve resistance to its toxins and whether B. thuringiensis is ecologically and genetically distinct from closely related strains that cause infections in humans and domestic animals. We found that natural bacterial populations in soil and on cabbage leaves were dominated by an insect-pathogen specialist genotype, and this genotype was better than its close relatives at establishing populations on leaves where its hosts were likely to be feeding. Spraying microbial pesticides and the addition of insect hosts increased the proportion of insect-pathogen specialists in the bacterial population, confirming that application of these biopesticides is a safe means of insect control. Populations of B. thuringiensis were transient on plant material, suggesting that selective pressure for resistance can be similarly transient. However, the genotype that dominates the natural community has been economically exploited more than any other, and selection for resistance to this strain may have occurred in natural populations of insects prior to the use of B. thuringiensis in pest control.
登录
查看更多内容
影响因子：
3.6
作者：
Bizzarri, M. F.;Bishop, A. H.
通讯作者：
Bishop, A. H.
影响因子：
3.3
作者：
Didelot, Xavier;Falush, Daniel
通讯作者：
Falush, Daniel
DOI：
10.1099/00221287-144-11-3049
发表时间：
1998-11-01
期刊：
MICROBIOLOGY-UK
影响因子：
--
作者：
Enright, MC;Spratt, BG
通讯作者：
Spratt, BG
DOI：
10.1073/pnas.0402414101
发表时间：
2004-06-01
影响因子：
11.1
作者：
Hoffmaster, AR;Ravel, J;Fraser, CM
通讯作者：
Fraser, CM
DOI：
10.1073/pnas.94.8.3519
发表时间：
1997-04-15
影响因子：
11.1
作者：
Gould, F;Anderson, A;Laster, M
通讯作者：
Laster, M