The first engagement of partners in the Euprymna scolopes-Vibrio fischeri symbiosis is a two-step process initiated by a few environmental symbiont cells.
Altura MA, Heath-Heckman EA, Gillette A, Kremer N, Krachler AM, Brennan C, Ruby EG, Orth K, McFall-Ngai MJ. Environ Microbiol. 2013 Nov; 15(11):2937-50. Epub 2013 Jul 3.