23.1 Wednesday, Jan. 4 Language barriers among bacteria: Cooperation and cheating in a squid-Vibrio symbiosis CASTLE, Wendy; NISHIGUCHI, Michele K.*; New Mexico State University; New Mexico State University email@example.com
The sepiolid squid-Vibrio fischeri symbiosis is a well developed model for the study of mutualistic associations. Bioluminescent bacteria are housed in specialized light organs in the mantle cavity of the squid where light is used by for silhouette reduction. Previous data suggests that light production may cost V. fischeri as much as twenty-five percent of their energetic output. Given the shared nature of the benefit (increased host survival), individual cost to bacteria, and the cooperative nature of luminescence regulation, this system is vulnerable to invasion by non-cooperative “cheaters” either at initiation of the infection or through mutation. Recent theory papers have suggested this particular mutualism is maintained through “screening” of partners. However, we find evidence that strains of “bright” and “dim” Vibrio are consistently isolated from the same lobe of the light organ of the same individual host. We find evidence that relatedness among co-occurring bright and dim strains is inconsistent. Additionally, we find that the frequency of dim strains is higher than that of bright strains in all hosts examined (frequency dependent selection). A more complex hypothesis of social interactions among these mutualistic polyclonal bacterial communities is supported with the evidence that isolates from the same light organ have differential responses to quorum sensing signals (QS) which regulate the costly luminescence production. This leaves open the possibility that QS signals may act as a form of policing and may be vulnerable to manipulation. Understanding the social consequences of competing bacteria in this environmentally transmitted symbiosis can provide insight into the subtlties of alleopathic interactions among competing mutualistic vibrios.