Determination of microbial numbers in anaerobically digested biofertilisers

Area of Science:

• Microbiology
• Environmental Science
• Agricultural Science

Background:

• Liquid anaerobic digestates (LADs) are potential biofertilisers.
• Understanding microbial communities in LADs is crucial for assessing their efficacy and safety.
• Previous studies have not comprehensively quantified bacterial, archaeal, and fungal populations across diverse commercial LADs.

Purpose of the Study:

• To quantify total bacterial, fungal, and archaeal numbers in various commercial liquid anaerobic digestates.
• To identify common microbial patterns and assess the implications for biofertiliser use.
• To investigate relationships between microbial populations and the physical-chemical properties of digestates.

Main Methods:

• Quantification of bacteria, fungi, and archaea using both culturable (CFU) and molecular (quantitative PCR, qPCR) methods.
• Analysis of gene copy numbers (GCN) for bacterial (16S rRNA), archaeal (16S rRNA), and fungal (18S rRNA) targets.
• Statistical analysis to determine significant differences in microbial numbers and correlations with physical-chemical traits.

Main Results:

• Bacterial and fungal colony-forming units (CFUs) varied significantly across digestates (10^5-10^10 and 0-10^5 g^-1 DW, respectively).
• Gene copy numbers (GCN) showed bacteria (10^8-10^10 g^-1 DW) dominated over archaea (10^7-10^9 g^-1 DW) and fungi (10^4-10^6 g^-1 DW).
• Despite variations, microbial profiles clustered into two main groups, indicating general similarity, with higher bacterial GCN linked to low organic matter and C/N ratio.

Conclusions:

• Liquid anaerobic digestates are primarily dominated by bacterial populations.
• The microbial communities in LADs exhibit a degree of similarity, supporting their potential as biofertilisers.
• Specific physical-chemical properties, like low organic matter and C/N ratio, correlate with higher bacterial abundance.