Isolation and identification of iron-reducing bacteria from gley soils

Seventy-one facultative anaerobic bacteria, capable of reducing iron oxide in pure culture, were isolated from three differently gleyed subsoils. The bacteria were picked at random from poured plates (10⁻⁵ and 10⁻⁶) inoculated with serially diluted soil samples. An attempt was made to identify these strains by morphological and biochemical tests. Among these 71 iron-reducing bacteria, all except three were capable of reducing nitrate to nitrite and 35 reduced nitrite further into gaseous compounds (denitrification), but only one strain (Bacillus subtilis) produced H₂S. Based upon their physiological and morphological properties, 38 strains were allotted to the genus Pseudomonas, 31 sporeformers to the genus Bacillus and two were regarded to be coryneform (Arthrobacter?) bacteria. Species identified were Ps. denitrificans (23), ps. stutzeri (8) ps. fluorescens-putida (5), Bacillus cereus (6), B. cereus var. mycoides (14) and Bacillus subtilis (9). Two spore-forming bacilli, two non-pigmented pseudomonads and two coryneform type of bacteria could not be identified. The significance of the enzyme nitrate reductase (nitratase) of these bacteria for anaerobic respiration and as a mechanism of iron reduction is discussed.