Morganella psychrotolerans sp. nov., a histamine-producing bacterium isolated from various seafoods

Mesophilic Morganella morganii (n=6) and psychrotolerant M. morganii-like isolates from various seafoods (n=13), as well as clinical M. morganii isolates (n=3), were characterized by using a polyphasic approach including multi-locus sequencing. Based on the phylogenetic analysis, the 22 strains were divided into two distinct groups comprising mesophilic and psychrotolerant isolates, respectively. This classification was supported by DNA-DNA hybridization studies, whereby a psychrotolerant isolate (strain U2/3(T)) showed 41.0 and 17.8 % relatedness to the type strains of the mesophilic species Morganella morganii subsp. morganii (strain LMG 7874(T)) and Morganella morganii subsp. sibonii (strain DSM 14850(T)), respectively. Analysis of the 16S rRNA gene sequences showed a similarity of 98.6 % between mesophilic and psychrotolerant isolates. However, fragments of seven protein-encoding housekeeping genes (atpD, dnaN, gyrB, hdc, infB, rpoB and tuf) all showed less than 90.9 % sequence similarity between the two groups. The psychrotolerant isolates grew at 0-2 degrees C and also differed from the mesophilic M. morganii isolates with respect to growth at 37 degrees C and in 8.5 % (w/v) NaCl and fermentation of d-galactose. The psychrotolerant strains appear to represent a novel species, for which the name Morganella psychrotolerans sp. nov. is proposed. The type strain is U2/3(T) (=LMG 23374(T)=DSM 17886(T)).