Erin Banning, Biology*

Examination of predatory behavior of coastal Flavobacterial isolates


Recent reports suggest that predatory bacteria include a wide variety of novel organisms which may act as important top-down regulators of microbial communities in many environments. In an exploration of whether predatory bacteria are present in the Cape Cod aquifer, we isolated three strains of marine predatory Flavobacteria and have further found that two type strains of Flavobacteria are predatory. This work is the first report, of which we are aware, showing that some Flavobacteria can grow predatorily – i.e., they can utilize living prey bacteria as their sole carbon source (Banning, Casciotti and Kujawinski, submitted). If this behavior is widespread amongst Flavobacteria in the oceans, it could represent a heretofore unanticipated path for biomass remineralization in the marine microbial loop.
Our initial work has been conducted with two-component predator-prey systems in which the prey are not actively growing. For the second data chapter of my thesis, we are extending this work to explore the predatory biology of Flavobacteria under more realistic conditions. The effects of different attributes of more complex prey communities are being independently tested in a series of experiments investigating the following questions:
1. Do predatory Flavobacteria discriminate between different susceptible prey organisms? Predatory Flavobacteria are being grown in co-culture with (a) mixtures of susceptible prey bacteria and (b) mixtures of susceptible and non-susceptible prey possessing different cell wall structures and phylogenies. The persistence or disappearance of each prey organism during predation will be assessed using fluorescent probes specific for each member of the co-culture. An ability to discriminate between susceptible prey might indicate a tightly controlled mechanism for engaging and lysing prey on a cell-by-cell basis.
2. How many predatory Flavobacteria cells are necessary for the clearing of susceptible prey?
The next set of experiments is designed to determine whether there is a minimum density of predator cells required for predation to take place. The number of predator cells required for successful predation has implications for the mechanism of predation and the effectiveness of predation in the environment. Our preliminary experiments have suggested that the addition of a single predatory cell can result in the clearing of an entire prey community. We are now initiating an experiment to confirm this result with microscopic analyses over a highresolution time course.
3. Can growing prey communities resist clearing by predatory Flavobacteria either by outgrowing them or forming biofilm structures that are predation-resistant?
Predatory Flavobacteria will be inoculated onto prey communities growing on defined media with varying concentrations of the prey growth substrate to explore whether a prey community is more robust to predation in higher growth states. If this is the case, the predatory Flavobacteria under study may be more likely to act as scavengers lysing inactive cells rather than as grazers significantly regulating active microbial communities. Given the current lack of appropriate genetic markers for bacterial predation, the predatory biology of these two coastal Flavobacterial isolates is best studied in culture. The planned experiments will provide important insights into their predatory biology and possible importance as top-down regulators of microbial communities and carbon cycling in coastal aquatic and sedimentary environments. The requested funds, outlined in the attached budget, will be used to pay for laboratory supplies required to execute the experiments and microscope time to analyze the results. The results of these experiments will comprise one of my thesis chapters and support a publication focused on the predatory biology of the strains of Flavobacteria that we have isolated, with a focus on the implications for the ecological and environmental significance of predatory Flavobacteria.