The screening of xanthomonas lactose - positive strains among bacterial populations of citrus canker disease isolated from Iran

Xanthan is a heteropolysaccharide that is produced by the group of plant pathogen bacteria from Xanthomonas genus. Usually، the media containing glucose، sucrose and starch is used for xanthan production. Because their preparation and transferring is expensive، the final cost of xanthan production by these carbon sources is high. On the other hand، many Xanthomonas species such as X. campestris are not able to use cheap media rich of lactose such as whey to produce xanthan due to the low expression and sometimes the defect of their β-galactosidase enzyme. The access to bacterial strains capable of decomposing lactose will provide a possibility for producing a valuable commercial product (xanthan) from an inexpensive carbon source (whey). In the present study، a collection containing 210 isolated Xanthomonas citri subsp. citri Iranian strains from citrus orchards in south Iran was studied. Then، the genus of these bacteria was determined by using molecular techniques and sequencing of 16S-rDNA gene. Also، their growth in lactose – based medium was investigated. Among 210 strains، 27 strains were able to grow on lactose rich medium. Then، the genus of these bacteria was proved by sequencing of 16S-rDNA gene and comparison with another 16S-rDNA gene sequences existing in NCBI. Also، these bacteria had considerable growth in lactose-based medium. Discussion and At last، we can say that separated lactose-positive Xanthomonas strains from southern citrus orchards have good ability to utilize lactose and in the near future، it would be possible to apply these native strains for xanthan production in cheaper lactose media such as whey.