Abstract: In this experiment，Fusarium oxysporum f. sp. cucumerium was used as the research object. The presence of symbiotic bacteria outside and inside the hyphae of F. oxysporum f. sp. cucumerium was determined by fluorescent nucleic acid staining and electron microscopy. The symbiotic bacteria were successfully isolated by plate culture method and dentified by 16S rDNA sequencing. It was determined that it belonged to Achromobacter spp. The analysis of carbon source utilization showed that compared with F. oxysporum f. sp. cucumerium without symbiotic bacteria，the Shannon index and anti-Simpson index of F. oxysporum f. sp. cucumerium with symbiotic bacteria were significantly increased by 2.18% and 1.67% respectively，and the utilization ability of sugars，carboxylic acids，amines，polymers and other carbon sources was strong，while the utilization ability of amino acids was weak. The results showed that there was symbiotic bacteria of Achromobacter spp. in F. oxysporum f. sp. cucumerium，and it may affect the growth and metabolic capacity of the host fungus.

Key words: cucumber, Fusarium oxysporum f. sp. cucumerium, symbiotic bacteria, isolation and identification, carbon source utilization