Department of Integrative Biology, University of California, Berkeley, Berkeley, CA, USA.
Infect Immun. 2013 Feb;81(2):514-20. doi: 10.1128/IAI.00653-12. Epub 2012 Dec 10.
The importance of our inner microbial communities for proper immune responses against invading pathogens is now well accepted, but the mechanisms underlying this protection are largely unknown. In this study, we used Caenorhabditis elegans to investigate such mechanisms. Since very little is known about the microbes interacting with C. elegans in its natural environment, we began by taking the first steps to characterize the C. elegans microbiota. We established a natural-like environment in which initially germfree, wild-type larvae were grown on enriched soil. Bacterial members of the adult C. elegans microbiota were isolated by culture and identified using 16S rRNA gene sequencing. Using pure cultures of bacterial isolates as food, we identified two, Bacillus megaterium and Pseudomonas mendocina, that enhanced resistance to a subsequent infection with the Gram-negative pathogen Pseudomonas aeruginosa. Whereas protection by B. megaterium was linked to impaired egg laying, corresponding to a known trade-off between fecundity and resistance, the mechanism underlying protection conferred by P. mendocina depended on weak induction of immune genes regulated by the p38 MAPK pathway. Disruption of the p38 ortholog, pmk-1, abolished protection. P. mendocina enhanced resistance to P. aeruginosa but not to the Gram-positive pathogen Enterococcus faecalis. Furthermore, protection from P. aeruginosa was similarly induced by a P. aeruginosa gacA mutant with attenuated virulence but not by a different C. elegans-associated Pseudomonas sp. isolate. Our results support a pivotal role for the conserved p38 pathway in microbiota-initiated immune protection and suggest that similarity between microbiota members and pathogens may play a role in such protection.
我们的内部微生物群落对于对抗入侵病原体的适当免疫反应非常重要，这一点现在已经得到广泛认可，但这种保护的机制在很大程度上还不清楚。在这项研究中，我们使用秀丽隐杆线虫来研究这种机制。由于人们对在其自然环境中与秀丽隐杆线虫相互作用的微生物知之甚少，因此我们首先着手描述秀丽隐杆线虫的微生物组。我们建立了一个类似于自然的环境，最初无菌的野生型幼虫在富含土壤的环境中生长。通过培养分离成年秀丽隐杆线虫微生物组的细菌成员，并使用 16S rRNA 基因测序进行鉴定。使用细菌分离物的纯培养物作为食物，我们鉴定出两种细菌，巨大芽孢杆菌和门多萨假单胞菌，它们增强了对随后革兰氏阴性病原体铜绿假单胞菌感染的抵抗力。虽然巨大芽孢杆菌的保护作用与产卵减少有关，这与生育力和抵抗力之间的已知权衡有关，但门多萨假单胞菌赋予的保护机制依赖于 p38 MAPK 途径调节的免疫基因的弱诱导。p38 直系同源物 pmk-1 的破坏消除了保护作用。门多萨假单胞菌增强了对铜绿假单胞菌的抵抗力，但对革兰氏阳性病原体粪肠球菌没有作用。此外，铜绿假单胞菌 gacA 突变体（毒力减弱）同样诱导了对铜绿假单胞菌的抵抗力，但不同的与秀丽隐杆线虫相关的假单胞菌分离物则没有。我们的结果支持保守的 p38 途径在微生物群引发的免疫保护中的关键作用，并表明微生物群成员与病原体之间的相似性可能在这种保护中发挥作用。
