Rahnella perminowiae sp. nov., Rahnella bonaserana sp. nov., Rahnella rivi sp. nov. and Rahnella ecdela sp. nov., isolated from diverse environmental sources, and emended description of the genus Rahnella

Bacteria isolated from onion bulbs suffering from bacterial decay in the United States and Norway were previously shown to belong to the genus Rahnella based on partial housekeeping gene sequences and/or fatty acid analysis. However, many strains could not be assigned to any existing Rahnella species. Additionally, strains isolated from creek water and oak as well as a strain with bioremediation properties were assigned to Rahnella based on partial housekeeping gene sequences. The taxonomic status of these 21 strains was investigated using multilocus sequence analysis, whole genome analyses, phenotypic assays and fatty acid analysis. Phylogenetic and phylogenomic analyses separated the strains into five clusters, one of which corresponded to Rahnella aceris. The remaining four clusters could be differentiated both genotypically and phenotypically from each other and existing Rahnella species. Based on these results, we propose the description of four novel species: Rahnella perminowiae sp. nov. (type strain SL6^T=LMG 32257^T=DSM 112609^T), Rahnella bonaserana sp. nov. (H11b^T=LMG 32256^T=DSM 112610^T), Rahnella rivi sp. nov. (FC061912-K^T=LMG 32259^T=DSM 112611^T) and Rahnella ecdela sp. nov. (FRB 231^T=LMG 32255^T=DSM 112612^T).

Fate and Persistence of a Pathogenic NDM-1-Positive Escherichia coli Strain in Anaerobic and Aerobic Sludge Microcosms

The presence of emerging biological pollutants in treated wastewater effluents has gained attention due to increased interest in water reuse. To evaluate the effectiveness of the removal of such contaminants by the conventional wastewater treatment process, the fate and decay kinetics of NDM-1-positive Escherichia coli strain PI7 and its plasmid-encoded antibiotic resistance genes (ARGs) were assessed in microcosms of anaerobic and aerobic sludge. Results showed that E. coli PI7 decayed at a significantly lower rate under anaerobic conditions. Approximate half-lives were 32.4 ± 1.4 h and 5.9 ± 0.9 h in the anaerobic and aerobic microcosms, respectively. In the aerobic microcosms, after 72 h of operation, E. coli PI7 remained detectable, but no further decay was observed. Instead, 1 in every 10,000 E. coli cells was identified to be recalcitrant to decay and persist indefinitely in the sludge. ARGs associated with the E. coli PI7 strain were detected to have transferred to other native microorganisms in the sludge or were released to the liquid fraction upon host decay. Extracellular DNA quickly degraded in the liquid fraction of the aerobic sludge. In contrast, no DNA decay was detected in the anaerobic sludge water matrix throughout the 24-h sampling period. This study suggests an increased likelihood of environmental dispersion of ARGs associated with anaerobically treated wastewater effluents and highlights the potential importance of persister cells in the dissemination of E. coli in the environment during reuse events of treated wastewater.

IMPORTANCE This study examines the decay kinetics of a pathogenic and antibiotic resistant strain of Escherichia coli in microcosms simulating biological treatment units of aerobic and anaerobic sludge. The results of this study point at a significantly prolonged persistence of the E. coli and the associated antibiotic resistance gene in the anaerobic sludge. However, horizontal transfer of the plasmid encoding the antibiotic resistance gene was detected in the aerobic sludge by a cultivation method. A subpopulation of persister E. coli cells was also detected in the aerobic sludge. The findings of this study suggest potential areas of concern arising from pathogenic and antibiotic-resistant E. coli during both anaerobic and aerobic sludge treatment processes.