Several batch studies have compared the effects of different inocula on CO conversion processes under consistent operational conditions . These investigations have employed 16S rRNA gene sequencing to examine the relationship between microbial community composition and inoculum type; however, they have been limited to batch setups and suspended cultures. While these approaches provide valuable insights, they do not accurately reflect the dynamics of continuous flow system and real-world operations, particularly in TBRs where biofilm formation plays a critical role. The mechanisms governing microbial selection and biofilm development in TBRs remain poorly understood, especially in relation to the initial inoculum source. A key knowledge gap exists in understanding how different inocula influence biofilm communities and reactor performance in continuous systems like TBRs. Unlike suspended cultures, biofilms exhibit distinct microbial compositions and metabolic interactions, which can significantly impact CO conversion efficiency. Furthermore, while 16S rRNA sequencing has been widely used to study microbial communities in batch cultures, its application in biofilm-based TBRs remains limited, often lacking the reliability needed to characterize biofilm-specific community structures and their functional impact on reactor performance. Addressing these gaps is essential for optimizing biofilm resilience and metabolic efficiency in In this study, we examined the effects of varying inoculum types on CO conversion performance in TBRs. The goal was to understand how inoculum-based variations influence TBR efficiency and microbial selection during biofilm formation. Three identical TBR systems, each containing the same packing materials and supplied with CO as the sole carbon and energy source, were employed to ensure comparability across conditions. The reactors were operated under uniform conditions for 125 days, using three inoculum sources: anaerobic sludge (AS) from a wastewater treatment plant (WWTP), anaerobic digestate (AD) from a biogas plant, and cow manure (CM). This design allowed us to systematically investigate the influence of inoculum sources on microbial community dynamics and reactor performance.