Few publications report the occurrence of bacteria associated with fungal cells. The presence of bacteria associated with one strain of (Fr.) P. Kumm. was described in the literature. We describe the biodiversity of bacteria associated with eight oyster mushroom strains from Japan, Poland, and the USA. The presence of microorganisms associated with all tested strains was confirmed using fluorescent microscopy. Among 307 sequences, 233 of clones representing 34 genera and 74 sequences were identified as . Most of the bacteria associated with the strain PUSAS were related to and two clones were related to genus. The biodiversity of clones isolated from fungal strains originating from Japan and Poland ranged from 15 to 32 different bacterial clones. The most often the bacteria related to genus , and were associated with the strains of fungi mentioned above. Laccase-like (LMCO) genes were identified in whole bacterial DNA isolated from the associated bacteria but β-glucosidase and β-xylanase genes were not detected.Few publications report the occurrence of bacteria associated with fungal cells. The presence of bacteria associated with one strain of (Fr.) P. Kumm. was described in the literature. We describe the biodiversity of bacteria associated with eight oyster mushroom strains from Japan, Poland, and the USA. The presence of microorganisms associated with all tested strains was confirmed using fluorescent microscopy. Among 307 sequences, 233 of clones representing 34 genera and 74 sequences were identified as . Most of the bacteria associated with the strain PUSAS were related to and two clones were related to genus. The biodiversity of clones isolated from fungal strains originating from Japan and Poland ranged from 15 to 32 different bacterial clones. The most often the bacteria related to genus , and were associated with the strains of fungi mentioned above. Laccase-like (LMCO) genes were identified in whole bacterial DNA isolated from the associated bacteria but β-glucosidase and β-xylanase genes were not detected.