The samples were taken below
the tidal zone of the sandy beach of a lagoon (1.5 m water
depth). The top 5-cm depth sediments until the suboxic
zone, just below the OATZ, were collected (Suppl data 2).
Sediments (150 mL) and marine water (300 mL) were
sampled in eight 500 mL plastic bottles containing 10 %
(v/v) air phase. Magnetotactic bacteria were magnetically
collected the same day in the laboratory from eight bottles
after homogenisation of the samples by placing the south
pole of 0.4 T permanent magnets against the outer surface
of the bottles [4]. After 30 min, bacteria in the brownblackish
spots underneath the magnets were collected with
a pipette, counted and inspected using the hanging-drop
approach [4], and magnetically purified by the race-track
method using 0.4 T permanent magnets, as previously
described [24]. Purified MTB were used for microscope
observations and DGGE analyses