A bioluminescent bacterial survey from marine ecosystems of Puerto Rico for the determination of their potential use as biosensors

Abstract

Bioluminescence is the phenomenon by which living organisms emit light through an organic oxidation catalyzed by the enzyme luciferase. These luminescent organisms have been discovered in all kinds of ecosystems. Among their diversity, bacteria are the most widespread and abundant bioluminescent organism in nature supporting a unique and necessary ecological role. Research on bioluminescent bacteria had led to the discovery of quorum sensing in which cells can chemically detect their presence and execute various processes crucial for competition such as extracellular transport of virulent factors, plasmid replication, catabolic pathways and light emission. In addition, luciferase coding genes (luxAB) have been cloned and express in other biological models with the purpose of biosensing molecules that trigger changes in light emission. The main objective of this study is to evaluate the presence of bioluminescent bacteria in marine ecosystems of Puerto Rico. Among the methods used are Gram stain and morphology confirmation through Scanning Electron Microscopy (SEM). In addition, biochemical assays were performed to test their potential enzymatic capability to metabolize different energy sources such as glycerol, mannitol, starch and sucrose. Phylogeny was done by sequencing both 16S rDNA and luxAB amplicons. As a final objective several isolates were exposed to phenanthrene to confirm growth and tolerance for their possible future use as biosensors. In silico analysis confirmed the presence of candidates closely related physiologically and molecularly to Photobacterium leiognathi and Vibrio harveyi. Eleven 16S rDNA sequences did not show close evolutionary relationship with previously reported strains based on neighborhood joining method. Only 14 sequences resulted to group close to the specie V. harveyi and only one strain was physiologically and molecularly related to the Photobacterium Family. The groups with the highest frequency in the collection are strains similar to the Vibrionaceae Family. This study is the first to report 32 partial sequences coding for luciferase from strains collected along the coast of Puerto Rico. Bioluminescent isolates also grew in presence of more than one antibiotic. In the collection, 66% of the candidates were resistant to ampicillin, 8% to tetracycline and 16% to kanamycin. This result suggests that these strains have mechanisms that contribute to their survival. This provides additional groups of bacteria that can clinically impact society and it will serve to report additional members of Vibrionaceae Family that are resistant to ampicillin and kanamycin.