Novel and efficient screening of PQQ high-yielding strains and subsequent cultivation optimization

A novel and efficient screening method for pyrroloquinoline quinone (PQQ) high-yielding methylotrophic strains was developed by using glucose dehydrogenase apoenzyme (GDHA) which depended on PQQ as the cofactor. Using this high-throughput method, PQQ high-yielding strains were rapidly screened out from thousands of methylotrophic colonies at a time. The comprehensive phylogenetic analysis revealed that the highest PQQ-producing strain zju323 (CCTCC M 2016079) could be assigned to a novel species in the genus Methylobacillus of the Betaproteobacteria. After systematic optimization of different medium components and cultivation conditions, about 33.4 mg/L of PQQ was obtained after 48 h of cultivation with Methylobacillus sp. zju323 at the shake flask scale. Further cultivations of Methylobacillus sp. zju323 were carried out to investigate the biosynthesis of PQQ in 10-L bench-top fermenters. In the batch operation, the PQQ accumulation reached 78 mg/L in the broth after 53 h of cultivation. By adopting methanol feeding strategy, the highest PQQ concentration was improved up to 162.2 mg/L after 75 h of cultivation. This work developed a high-throughput strategy of screening PQQ-producing strains from soil samples and also demonstrated one potential bioprocess for large-scale PQQ production with the isolated PQQ strain.