Metagenomic insights into the impacts of phytochemicals on bacterial and archaeal community structure and biogas production patterns during anaerobic digestion of avocado oil processing waste feedstocks

Phytochemicals are potent inhibitors of in vivo ruminal microbial activity and methanogenesis of plant materials. However, a knowledge gap exists on the influence of phytochemicals on microbial ecology and biomethane production under anaerobic bioreactor environment. In this study, high-throughput metagenomic sequencing and physicochemical analyses were used to evaluate the effects of phytochemicals on the microbial community structure and methane production efficiency of different avocado oil processing wastes under standard batch anaerobic digestion (AD) over the 30-day period. Results showed that the avocado wastes produced methane yields (MY) ranging from 79 to 247 mL CH4/gVS(added), with skin/peels (AS), cold-pressed pomace (CDP), cold-pressed wastewater (CDW), and hot-pressed pomace (HDP) digestates showing diauxic methane production patterns and peak daily methane production at day 7. Avocado seed (AK) digestate, characterized by high phytochemical content, exhibited a monophasic methane production pattern and the lowest MY. Pseudomonas, Romboutsia, Paeniclostridium, and Methanocorpusculum, Methanosaeta, Methanoregula, and Methanosarcina were the dominant bacterial and archaeal genera in all digesters. Lipolytic Pseudomonas were enriched in the early AD phase (0-15 days), whereas Romboutsia, Paeniclostridium, and Clostridium increased in the late AD stage (days 13-30). Spearman correlation analyses showed that the total polyphenols and saponins exhibited a significant negative influence on biomethane production. Alkaloid level significantly affected Romboutsia, Paeniclostridium, and Methanoregula, while saponins negatively correlated to AC160630, Clostridium, Methanocorpusculum, and Methanoregula. To the best of our knowledge, this is the first report on the potential negative impact of phytochemicals on the microbial community structure and biomethane production from avocado processing wastes.

Automated summary

This study evaluated the effects of phytochemicals on the microbial community structure and methane production efficiency of different avocado oil processing wastes using high-throughput metagenomic sequencing and physicochemical analyses. The results showed that phytochemicals had a significant negative impact on methane production, and different wastes exhibited different methane production patterns. Pseudomonas, Romboutsia, Paeniclostridium, and Methanocorpusculum, Methanosaeta, Methanoregula, and Methanosarcina were the dominant bacteria and archaea. In conclusion, this is the first report on the potential negative impact of phytochemicals on the microbial community structure and biomethane production from avocado processing wastes.