Effect of Pollutant Concentration During Isolation on the CH4 Biodegradation Kinetics, Population Structure and PHB Accumulation

Abstract

Methane-oxidizing bacteria were enriched in three stirred tank reactors continuously supplied with CH₄- laden air at 20, 2 and 0.2 gCH₄ m^-3 to assess the effect of pollutant concentration on the biodegradation kinetics, population structure and polyhydroxyalkanoate (PHA) production under sequential nitrogenlimitations. CH₄ concentration influenced the population structure of the enriched cultures, which were mainly constituted by type I and, in a lesser extent, by type II methanotrophs. Microorganisms enriched at 2 gCH₄ m^-3 presented the highest maximum specific degradation rate (q_max) and those enriched at 20 and0.2 gCH₄ m^-3 exhibited the lowest half-saturation constant (K_S), which ruled out a potential correlation between CH₄ concentration and kinetic parameters. Maximum polyhydroxybutyrate (PHB) contents of 1.0,12.6 and 1% (w/w) were obtained at 20, 2 and 0.2 gCH₄ m^-3, respectively. Polyhydroxyvalerate (PHV) was also detected at PHB:PHV ratios of up to 12:1 and 4:1 in the cultures enriched at 20 and 0.2 gCH₄ m^-3,respectively.