Characterisation of a flocculating strain of pseudomonas putida

Autoflocculation is a feature of some strains of Pseudomonas putida, a bacterium which is of interest commercially because it synthesises dehalogenases. Using shake flask cultures, it was shown that flocculation resulted from growth in magnesium-depleted conditions and the suggestion is made that flocculating strains of P. putida could have higher magnesium requirements than non-flocculating strains. Electron microscope evidence points towards some form of bridging mechanism for flocculation, possibly involving secreted polymers, rather than neutralisation of surface charge. Changes in cell shape were also observed in both flocculating and non-flocculating cultures grown in magnesium-depleted conditions. Measurements of floe strength and re-formation of floes after break-up tend to support the idea that flocculation could be of use in commercial downstream separation of cells.