Seasonal Variability of Magnetotactic Bacteria in a Freshwater Pond

Magnetotactic bacteria (MTB) synthesize ferrimagnetic crystals that contribute to the remanent magnetization in sediments, yet knowledge of how MTB populations vary in natural environments over time remains limited. We report abundances of three MTB morphotypes from nine sites collected and measured every month over a two-year period from a natural pond near Munich, Germany. Morphotype populations underwent coherent temporal trends among the nine sitesespecially at proximal sites with similar water depths. MTB populations varied independently of bottom water oxygen concentrations or temperature over the two-year period, except for spirilla, which flourished during the summer at some sites. Magnetic properties of the sediments did not reflect living MTB abundances, but instead varied with water depth. Deeper sites, which were also lower in organic carbon, nitrogen, and oxygen concentrations than shallower sites, had higher saturation magnetizations and were richer in single-domain particles.