Assessing the influence of CH4 concentration during culture enrichment on the biodegradation kinetics and population structure

Methanotrophic communities were enriched in three stirred tank reactors continuously supplied with CH4-laden air at 20, 2 and 0.2 gCH4 m−3 in order to evaluate the influence of CH4 concentration on the biodegradation kinetics, population structure and potential polyhydroxyalkanoate production under sequential nitrogen limitations. The population structure of the enriched cultures, dominated by type I methanotrophs, was influenced by CH4 concentration. No significant correlation between CH4 concentration and the maximum specific degradation rate (qmax) or the half-saturation constant (KS) was recorded, microorganisms enriched at 2 gCH4 m−3 presenting the highest qmax and those enriched at 20 and 0.2 gCH4 m−3 exhibiting the lowest KS. Maximum polyhydroxybutyrate (PHB) contents of 1.0% and 12.6% (w/w) were achieved at 20 and 2 g CH4 m−3, respectively. Polyhydroxyvalerate (PHV) was also detected at PHV:PHB ratios of up to 12:1 and 4:1 in the communities enriched at 20 and 0.2 gCH4 m−3, respectively. [Display omitted] •The enriched methanotrophic communities exhibited high species evenness and richness.•CH4 concentration significantly influenced the microbial population structure.•Dominance of type I methanotrophs regardless of the CH4 concentration.•The enriched methanotrophs exhibited high qmax and low KS values.•Maximum PHB cell contents were achieved by increasing CH4/biomass ratio.