NandaKafle Gitanjali, Seale Tarren, Flint Toby, Nepal Madhav, Venter Stephanus N, Brözel Volker S
Department of Biology and Microbiology, South Dakota State University.
Department of Microbiology and Plant Pathology, University of Pretoria.
Microbes Environ. 2017 Sep 27;32(3):226-233. doi: 10.1264/jsme2.ME17030. Epub 2017 Jul 27.
Escherichia coli is widely considered to not survive for extended periods outside the intestines of warm-blooded animals; however, recent studies demonstrated that E. coli strains maintain populations in soil and water without any known fecal contamination. The objective of this study was to investigate whether the niche partitioning of E. coli occurs between cattle and their pasture. We attempted to clarify whether E. coli from bovine feces differs phenotypically and genotypically from isolates maintaining a population in pasture soil over winter. Soil, bovine fecal, and run-off samples were collected before and after the introduction of cattle to the pasture. Isolates (363) were genotyped by uidA and mutS sequences and phylogrouping, and evaluated for curli formation (Rough, Dry, And Red, or RDAR). Three types of clusters emerged, viz. bovine-associated, clusters devoid of cattle isolates and representing isolates endemic to the pasture environment, and clusters with both. All isolates clustered with strains of E. coli sensu stricto, distinct from the cryptic species Clades I, III, IV, and V. Pasture soil endemic and bovine fecal populations had very different phylogroup distributions, indicating niche partitioning. The soil endemic population was largely comprised of phylogroup B1 and had a higher average RDAR score than other isolates. These results indicate the existence of environmental E. coli strains that are phylogenetically distinct from bovine fecal isolates, and that have the ability to maintain populations in the soil environment.
大肠杆菌被广泛认为在温血动物肠道外无法长时间存活;然而,最近的研究表明,大肠杆菌菌株在没有任何已知粪便污染的土壤和水中维持种群数量。本研究的目的是调查大肠杆菌在牛及其牧场之间是否存在生态位分化。我们试图阐明来自牛粪的大肠杆菌在表型和基因型上是否与在牧场土壤中越冬维持种群数量的分离株不同。在牛引入牧场前后采集土壤、牛粪和径流样本。通过uidA和mutS序列以及系统发育分组对363个分离株进行基因分型,并评估其卷曲形成(粗糙、干燥和红色,或RDAR)情况。出现了三种类型的聚类,即与牛相关的聚类、不含牛分离株且代表牧场环境特有分离株的聚类以及两者都有的聚类。所有分离株都与狭义大肠杆菌菌株聚类,与隐秘种进化枝I、III、IV和V不同。牧场土壤特有种群和牛粪种群的系统发育分组分布非常不同,表明存在生态位分化。土壤特有种群主要由系统发育分组B1组成,其平均RDAR得分高于其他分离株。这些结果表明存在与牛粪分离株在系统发育上不同的环境大肠杆菌菌株,并且它们有能力在土壤环境中维持种群数量。