Constant flux of spatial niche partitioning through high-resolution sampling of magnetotactic bacteria

Abstract

Magnetotactic bacteria (MTB) swim along magnetic field lines in water. They are found in aquatic habitats throughout the world, yet knowledge of their spatial and temporal distribution remains limited. To help remedy this, we took MTB-bearing sediment from a natural pond, mixed the thoroughly homogenized sediment into two replicate aquaria, and then counted three dominant MTB morphotypes (coccus, spirillum, and rod-shaped MTB cells) at a high spatiotemporal sampling resolution: 36 discrete points in replicate aquaria were sampled every ~30 days over 198 days. Population centers of the MTB coccus and MTB spirillum morphotypes moved in continual flux, yet they consistently inhabited separate locations, displaying significant anticorrelation. Rod-shaped MTB were initially concentrated toward the northern end of the aquaria, but at the end of the experiment, they were most densely populated toward the south. The finding that the total number of MTB cells increased over time during the experiment argues that population reorganization arose from relative changes in cell division and death and not from migration. The maximum net growth rates were 10, 3, and 1 doublings day-1 and average net growth rates were 0.24, 0.11, and 0.02 doublings day-1 for MTB cocci, MTB spirilla, and rod-shaped MTB, respectively; minimum growth rates for all three morphotypes were -0.03 doublings day-1. Our results suggest that MTB cocci and MTB spirilla occupy distinctly different niches: their horizontal positioning in sediment is anticorrelated and under constant flux.