Evaluation of the influence of the gas residence time and biomass concentration on methane bioconversion to ectoines in a novel Taylor flow bioreactor

Today, the use of biogas to produce more sustainable bioproducts is attracting an increasing attention in the quest for a circular economy. This work aims at optimizing the biosynthesis of high value bioproducts such as ectoine and hydroxyectoine from methane using a high mass transfer Taylor flow reactor and a methanotrophic consortium. The influence of the gas residence time (30-240 min) and concentration of microorganisms (0.1-1.8 g TSS·L^-1) on methane bioconversion and ectoine production was evaluated. The maximum methane bioconversion efficiency reached was ∼90% at a gas residence time of 240 min. Biological limitation in the reactor was observed at concentrations below 0.5 g total suspended solids (TSS)·L^-1. The intracellular ectoine and hydroxyectoine content did not experience large variations with the gas residence time and biomass concentration. The maximum ectoine content was 49.0 ± 16.1 mg_EC·g_TSS^-1 at a gas residence time of 240 min and a biomass concentration of 0.7 g TSS·L^-1. The maximum hydroxyectoine content was 13.0 ± 3.6 and 12.7 ± 2.2 mg_HE·g_TSS^-1 at a gas residence time of 240 min and biomass concentrations of 1.8 and 1.2 g TSS·L^-1, respectively. Methylophaga and Methylomicrobium were the dominant methanotrophs in the bioreactor regardless of the gas residence time and biomass concentration. Microorganisms belonging to the genera Paracoccus, Methylophaga, Methylomicrobium and Nitratireductor have been identified as ectoines producers or have been found to possess genes responsible for ectoines synthesis.