Evidence of bacterial bioluminescence in a Philippine squid and octopus hosts

Bioluminescence is the light emission from living organisms. Despite the tremendous biodiversity existing in the vast and numerous aquatic habitats of the Philippines, bioluminescent bacteria are one of the most poorly studied organisms in the country. In this study, Philippine marine organisms were investigated for the presence of symbiotic bioluminescent bacteria. Bioluminescent bacteria were consistently isolated from marine squid and octopus samples. Based on morphology, the squid commonly known in the Philippines as pusit lumot was identified as Photololigo sp. of family Loliginidae, and the octopus commonly known in the Philippines as pugita was identified as Cistopus sp. belonging to family Octopodidae. Sequence analysis of the 16S rRNA gene of the bioluminescent bacterial isolates from the squid and octopus samples, designated as strains ADMU-01 and ADMU-02 respectively, showed that they are both closely related to both Photobacterium mandapamensis and Photobacterium leiognathi with 99% identity. Phylogenetic analysis showed that the isolates clustered with known representatives of marine bioluminescent bacterial symbionts under the Family Vibrionaceae under which Photobacterium spp. belong. To date, this is the first report on the molecular identification and phylogenetic analysis of Philippine bioluminescent bacterial isolates. Most remarkably, this is the first report on the evidence of bacterial luminescence in an octopus, an organism whose bioluminescent counterparts are typically known to emit light only through surface photophores.