Bacteriocin/Antibiotic Production and Sensitivity Among
Bacteria Isolated from Zebra Mussel Shells
Kelly Gross
Department of Biology
Marquette University
Dr. James Maki

 The accidental introduction of zebra and quagga mussels to the Great Lakes has resulted in billions of dollars spent annually to repair the damage caused from biofouling by these two bivalve species.  Many biological factors influence the recruitment of mussel larvae in the environment.  A study performed in Lake Erie suggested that the biofilm on mussel shells played an important role in larval recruitment to that surface, and upon its removal, recruitment was reduced by as much as 10-20% (Wainman et al. 1996).  This study noted that there was an indication that some factor associated with the shell, whether chemical or physical, was "significant in encouraging recruitment."

The focus of this project was an investigation of the potential influence bacteria may have on larval recruitment.  In particular, the initial scope of the project centered on bacteriocin or antibiotic production by strains of bacteria isolated from zebra mussel shells.  Numerous bacteria in the environment produce antibiotic-like substances.  Thus, it was pertinent to consider them as a potential factor in larval recruitment.

Initially, the isolated bacteria were screened for bacteriocin production using the agar overlay method (Pitt and Gaston 1995).  A positive test was indicated by a zone of inhibition around the producer colony as seen on the indicator bacterium lawn.  Various producer and sensitive strains were uncovered using this method.  In total, nineteen bacterial strains were examined, The experiment was repeated at least twice for each different bacterium.  So far, six producer strains, including both Gram positive and Gram negative bacteria, have been identified.  These data include only the strains which were reproducibly shown to be producers.  Data are still pending on six strains, which do not currently have enough supporting evidence to accurately label them as producer or sensitive strains.  On average, there were 4.5 sensitive strains found for each producer.  Two Gram positive strains in particular, JK009 and JK010, were found to be stronger producers compared to the production capabilities of the other four strains.  The criterion for this comparison was based on the size of the zone of inhibition around the bacterial colony.  The number of sensitive strains, both Gram positive and Gram negative, found for these two producers was nine. Currently, I am focusing on strain JK010 and determining in which growth phase(s) the bacteriocin or antibiotic is produced.

'Waimman, B.C., Hincks, S.S., Kaushik, N.K., and Macide, G.L. 1996.  Biofilm and Substrate Preference in the Dreisscnid Larvae of Lake Eric.  Can, J. Fish.  Aquat.  Sci. (Canada), 53: 134-140.  Pitt, Tyrone L., and Gaston, Michacl A. 1995.  Bacteriocin Typing-Chapter 2, Methods in Molecular Biology, 46: 9-1 1.