Quantity changes in Pseudomonas species in dairy manure during anaerobic digestion at mesophilic and thermophilic temperatures

Anaerobic digestion is known to eliminate many kinds of microorganisms in livestock wastes. In this study, the quantitative changes of Pseudomonas species during mesophilic and thermophilic anaerobic digestions were investigated with focus on P. aeruginosa and P. fluorescens, which are known as a pathogen and a plant growth-promoting rhizobacterium, respectively. Furthermore, quantitative changes in antimicrobial-resistant Pseudomonas species against cefazolin were also investigated as a representative of antimicrobial resistance in dairy farms. The quantitative measurement of Pseudomonas species was performed by a plating method with modified Pseudomonas-selective agar medium. The colonies on the agar plates were classified into three groups by their colour development and constitutional fluorescence, and the group to which P. aeruginosa and P. fluorescens belong was confirmed by colony PCR using species-specific primers. The results revealed that while the number of total Pseudomonas decreased, the number of fluorescent Pseudomonas including P. fluorescens increased after anaerobic digestion. The abundance of cefazolin-resistant Pseudomonas also decreased, and no P. aeruginosa could be detected in any samples. These results suggested that the digestate has benefits such as the absence of pathogenic risks led by the Pseudomonas species and is expected to have a plant growth-promoting effect facilitated by fluorescent Pseudomonas.