polynucleobacter difficilis polynucleobacter difficilis polynucleobacter difficilis is an aerobic, catalase- and oxidase-positive, chemo-organotrophic, nonmotile, freshwater bacterium of the genus polynucleobacter, isolated from the lake sevan from a depth of 60 m in armenia. polynucleobacter difficilis scientific classification domain: bacteria phylum: pseudomonadota class: betaproteobacteria order: burkholderiales family: burkholderiaceae genus: polynucleobacter species: p. difficilis binomial name polynucleobacter difficilishahn et al. 2012