Determination of the concentration of magnetotactic bacteria by means of susceptibility measurements

High concentrations of magnetotactic bacteria are needed for their practical applications, as investigations of domains in soft magnetic materials. The present paper reports experimental studies, the initial aim of which has been to determine the concentration c of magnetotactic bacteria within a culture medium from the measured susceptibility χ. A pure culture of Magnetospirillum gryphiswaldense as well as a natural population of cocci were investigated. M. gryphiswaldense showed a linear relation of the measured χ with the concentration c . Cocci showed characteristics which complicate the determination of c . Problems of manipulation of cocci by means of magnetic fields are discussed. For an effective interpretation of χ attempts were made to divide natural populations in sub-populations of more uniform characteristics by a magnetophoresis technique and by changing the polarity of bacteria.