Ecological interactions between marine microorganisms, such as allelopathy competition and symbiosis, are prevalent and important in the oceans. Here, we present a preliminary physiological and genomic characterization of two strains of marine Alteromonas, chosen based on strongly contrasting effects when grown in co-culture with Prochlorococcus, a globally-abundant marine primary producer: one enhances Prochlorococcus growth and one inhibits it. Significant differences were observed between the two strains, both in their growth rates and in their range of carbon substrate utilization. We are currently assembling the genome of one of the two Alteromonas strains, HOTo1A3, using a combination of de-novo and reference based assembly of a single 72 bp paired end library. Using this approach we have succeeded in reducing the number of the contigs from 300-700 to 13. Whereas initial read mapping suggested that HOTo1A3 is closest to ATCC 27126, a strain also isolated near Hawaii, many genes are in fact much more similar to those of strain isolated from the English Channel (673). This raises the question, of what processes (lateral gene transfer, recombination) shape these genomes. These results will help elucidate the molecular basis of the interactions between Alteromonas and Prochlorococus, and to search for such interactions in the marine environment.
