Isolation and physiological characterization of psychrophilic denitrifying bacteria from permanently cold A rctic fjord sediments ( S valbard, N orway)

Summary A large proportion of reactive nitrogen loss from polar sediments is mediated by denitrification, but microorganisms mediating denitrification in polar environments remain poorly characterized. A combined approach of most‐probable‐number ( MPN ) enumeration, cultivation and physiological characterization was used to describe psychrophilic denitrifying bacterial communities in sediments of three A rctic fjords in S valbard ( N orway). A MPN assay showed the presence of 10 3 −10 6 cells of psychrophilic nitrate‐respiring bacteria g −1 of sediment. Fifteen strains within the P roteobacteria were isolated using a systematic enrichment approach with organic acids as electron donors and nitrate as an electron acceptor. Isolates belonged to five genera, including S hewanella , P seudomonas , P sychromonas ( G ammaproteobacteria ), A rcobacter ( E psilonproteobacteria ) and H erminiimonas ( B etaproteobacteria ) . All isolates were denitrifiers, except S hewanella , which exhibited the capacity for dissimilatory nitrate reduction to ammonium ( DNRA ). Growth from 0 to 40° C demonstrated that all genera except S hewanella were psychrophiles with optimal growth below 15° C , and adaptation to low temperature was demonstrated as a shift from primarily C 16:0 saturated fatty acids to C 16:1 monounsaturated fatty acids at lower temperatures. This study provides the first targeted enrichment and characterization of psychrophilic denitrifying bacteria from polar sediments, and two genera, A rcobacter and H erminiimonas , are isolated for the first time from permanently cold marine sediments.