Isolation of lactate-degrading bacteria from anaerobic sludge in a thermophilic anaerobic digestion reactor treating poly(L-lactic acid)

This study aimed to isolate lactate-degrading bacteria via treatment with poly(L-lactic acid) (PLLA) in a thermophilic anaerobic digestion reactor to investigate their ecophysiological characteristics. Enrichment cultures were established with a basal medium (pH 7.0) supplemented with lactate and a thermophilic digester sludge as an inoculum, followed by anaerobic culturing at 55°C without shaking. Thereafter, 16S rRNA gene-based cloning analyses revealed that the predominant bacteria in the enrichment culture were of genus Moorella. Roll-tube cultures containing lactate and Moorella-resistant streptomycin were serially diluted to isolate Moorella cells from a series of the diluted enrichment cultures. Fluorescence in situ hybridization analyses using a Morl93 probe revealed that a pure culture of the strain (strain Hama-1) was successfully obtained. Phylogenetic analysis based on 16S rRNA gene sequences revealed that strain Hama-1 is closely related to Moorella perchloratireducens strain An10T with 99.6%...