Gut-Colonizing Bacteria Promote C. elegans Innate Immunity by Producing Nitric Oxide

Publication date: Available online 4 February 2016
Source:Cell Reports
Author(s): Yi Xiao, Fang Liu, Zhigang Zhang, Jie Tang, Cheng-Gang Zou, Ke-Qin Zhang
Many commensal bacteria in the gut are beneficial to the host immune system, but the underlying mechanisms are largely unclear. Using culture-independent Illumina MiSeq sequencing of the bacterial 16S rRNA gene amplicons, we show that bacterial diversity in the intestine of Caenorhabditis elegans, the free-living nematode, is distinct from that in soil. Of these bacteria, Bacillus subtilis is the most prominent species in the worm gut. We demonstrate that B. subtilis confers worm resistance to infection by pathogenic bacteria, such as Pseudomonas aeruginosa, Salmonella enterica, and Enterococcus faecalis, by producing nitric oxide (NO). Deletion of the nos gene, which encodes an NO synthase, reduces the protective effect. NO promotes innate immune responses to P. aeruginosa PA14 by activating a conserved p38 mitogen protein kinase (MAPK) in C. elegans. Our work provides an example of antagonism of commensal bacteria against pathogens and illustrates the importance of commensal bacteria in host immunity.

Graphical abstract

Teaser

B. subtilis is a symbiont that resides in the gut of C. elegans and generates nitric oxide that is essential for the host. Xiao et al. demonstrate that nitric oxide promotes defense against pathogenic bacteria by activating p38 MAPK, demonstrating the importance of commensal bacteria in host immunity.


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