Distribution of purple photosynthetic bacteria in wetland and woodland habitats of central and northern Minnesota

Enrichment cultures for purple nonsulfur and sulfur photosynthetic bacteria were prepared for soil samples collected in central and northern Minnesota. The purple nonsulfur bacteria were found in most wetland soils sampled but were uncommon in woodland and grassland soils. The pH range of the soils in which these bacteria occurred was 3.8-7.8 and the oxidation-reduction potential (Eh) ranges was +510 to -65 mV. Soils with a pH below 5.0 or an Eh above +370 mV had a few purple nonsulfur bacteria (<10/g of soil). Rhodopseudomonas viridis, a photosynthetic bacterium containing bacteriochlorphyll b, and the purple sulfur bacteria were common only in low-acidity wetland soils that were usually being reduced.