Isolation and Identification of Sulphite- and Iron Reducing, Hydrogenase Positive Facultative Anaerobes from Cooling Water Systems

Summary The significance of sulphidogenic facultative anaerobes in microbially influenced corrosion (MIC) has been overshadowed by extensive research on sulphate-reducing bacteria (SRB). An enrichment procedure with Modified Iron Sulphite (MIS) medium was employed to select for sulphidogenic facultative anaerobes from industrial cooling water systems. All isolates reduced sulphite and ferric iron, oxidised cathodic hydrogen on mild steel, and some oxidised cathodic hydrogen on stainless steel (3CR12). Facultative anaerobes generating sulphide from sulphite were identified by making use of biochemical tests, API 20 NE, BIOLOG, SDS-PAGE of the total soluble cell proteins, partial sequences of the 16S rRNA gene (rDNA) and RFLP-PCR. Our results show that Aeromonas isolated from cooling water systems, ie A. veronii biotype sobria, A. hydrophila and A. media can reduce both ferric to ferrous iron and sulphite to hydrogen sulphide in IS medium. The results further showed that these sulphidogenic bacteria are all capable of reducing cathodic hydrogen and therefore play a role in MIC.