Microbial diversity of Minnesota peatlands

Abstract

Microbial diversity, numbers, and metabolic activities in Minnesota peatlands were investigated using a variety of microbial enrichment and enumeration procedures together with radioisotopic measurements of microbial degradative processes. Minnesota peatlands were shown to contain large microbial populations of wide metabolic diversity. Direct counts of bacteria using epifluorescence microscopy indicated bacterial populations of about 10⁸ ml⁻¹ of peatland water, irrespective of depth. Radioisotopic most-probable-number (MPN) counts of heterotrophs able to mineralize¹⁴C-labeled substrates to¹⁴CO₂ showed significant populations of glucose degraders (10⁴–10⁶ ml⁻¹) as well as degraders of benzoate (10²–10³ ml⁻¹), 2,4-dichlorophenoxyacetate (10²–10⁵ ml⁻¹), and sphagnum (10³–10⁷ ml⁻¹) in the various peatlands examined. The MPNs of NO₃ ⁻ reducers varied from 10³–10⁶ ml⁻¹, SO₄ ⁻ reducers from 10²–10³ ml⁻¹, methanogenic bacteria from 10³–10⁶ ml⁻¹, and methane oxidizers from 10³–10⁴ ml⁻¹, depending on sampling site and depth. Eighty pure cultures of aerobic bacteria and fungi were isolated from Minnesota peats. Most of those cultures tested were able to grow on at least 20 organic compounds (carbohydrates, aromatic molecules, hydrocarbons, etc.) as sole sources of carbon and energy. One isolate, aBacillus, was able to fix atmospheric N₂. Several of the isolates were able to mineralize¹⁴C-labeled lignin.