Isolation and Identification of Autotrophic and Heterotrophic Bacteria from an Autohydrogenotrophic Pilot-plant for Denitrification of Drinking Water

Abstract

Summary The bacterial population of an autohydrogenotrophic pilot-reactor for denitrification of drinking water was characterized. Two samples were taken from the reactor under mesotrophic and psychrotrophic conditions, respectively. We purified 82 mesotrophs and 54 psychrotrophs. After screening by sodium dodecyl sulphate-polyacrylamide gelelectrophoresis of whole-cell proteins we obtained 30 and 36 different strains, respectively. These strains were identified by gaschromatographic fatty acid analysis, phenotypic tests (API), DNA-rRNA hybridizations and % G+C determination. Furthermore, their autohydrogenotrophic and heterotrophic denitrification capacities under mesotrophic or psychrotrophic conditions were tested. Some of the mesotrophs were assigned to: Aeromonas hydrophila (5 strains), Acinetobacter johnsonii (3 strains), Comamonas acidovorans (2 strains) and Shewanella putrefaciens (1 strain). The following identifications were obtained at the genus level: Serratia sp. (2 strains), Pseudomonas sp. (possibly P. stutzen, 4 strains, P. mendocina, 1 strain; P. syringae, 2 strains). Some of the psychrotrophs were assigned to: Shewanella putrefaciens (5 strains), Aeromonas hydrophila (1 strain), Aeromonas sobria (1 strain) and Micrococcus lylae (1 strain). The following identifications were obtained at the genus level: Acinetobacter sp. (16 strains) and Pseudomonas sp. (P. aureofaciens, 4 strains; P. syringae, 2 strains). The identification of the other strains was unreliable. Computer-assisted comparison of the individual strain data showed that Aeromonas hydrophila, Shewanella putrefaciens, Acinetobacter sp. and Pseudomonas sp. are present both in the mesotrophic and the psychrotrophic sample. None of the isolates was capable of autohydrogenotrophic denitrification. Under heterotrophic conditions, 7 Pseudomonas members and one unidentified isolate showed complete denitrification. This could indicate that the denitrification process in the reactor is not strictly autohydrogenotrophic or that the causal organisms were not yet isolated. Due to the presence of opportunistic human pathogens such as Aeromonas hydrophila, Shewanella putrefaciens, Acinetobacter sp. and Serratia sp. this denitrification reactor can only be used as a pretreatment step, which should be followed by a desinfection of the water.