Screening for Type II L-Asparaginases: Lessons from the Genus Halomonas

Among the two types of bacterial L-asparaginases, only type II enzymes have been used inthe treatment of acute lymphoblastic leukemia owing to their higher affinity for L-asparagine.However, current screening media used for the isolation of L-asparaginase-producingmicroorganisms do not discriminate between the two types of L-asparaginase. During anoptimization study conducted to increase L-asparaginase production by environmentalHalomonas isolates, it was noticed that the pattern of L-asparaginase production in responseto variations in glucose concentration varied between different isolates suggesting that theydiffer in their ability to produce type II L-asparaginases, an observation that was confirmed byfurther experiments. Bioinformatics analysis of available Halomonas whole genome sequencesrevealed that indeed some species of this genus possess both L-asparaginase types while otherspossess only type I enzymes. By comparing the growth pattern of these isolates on differentmedia, we propose that by omitting glucose, reducing the concentration of L-asparagine andproviding an alternative nitrogen source in L-asparaginase screening media it may be possibleto differentiate between type I and type II activities.