Cell Press, Cell Host & Microbe, 2(14), p. 183-194, 2013
DOI: 10.1016/j.chom.2013.07.006
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Upon transit to colonization sites, bacteria often experience critical priming that prepares them for subsequent, specific interactions with the host; however, the underlying mechanisms are poorly described. During initiation of the symbiosis between the bacterium Vibrio fischeri and its squid host, which can be observed directly and in real time, ~5 V. fischeri cells aggregate along the mucociliary membranes of a superficial epithelium prior to entering host tissues. Here we show that these few early host-associated symbionts specifically induce robust changes in host gene expression that are critical to subsequent colonization steps. This exquisitely sensitive response to its specific symbiotic partner includes the upregulation of a host endochitinase, whose activity hydrolyzes polymeric chitin in the mucus into chitobiose, thereby priming the symbiont and also producing a chemoattractant gradient that promotes V. fischeri migration into host tissues. Thus, the host responds transcriptionally upon initial symbiont contact, which facilitates subsequent colonization.