Ectoine bio-milking in methanotrophs: A step further towards methane-based bio-refineries into high added-value products

Abstract

Abstract:This communication showed for the first time that the methanotrophic strain Methylomicrobium alcaliphilum 20Z can efficiently synthesize and excrete (through a tailored bio-milking process) ectoine under continuous mode using methane as the sole energy and carbon source. First, three consecutive 50 h fed batch fermentations consisting of alternating high salinity (6% NaCl for 24h) and low salinity (0 % NaCl for 24h) cultivation stages were carried out in triplicate to determine the influence of sudden modifications in media salinity on ectoine synthesis and excretion. The results demonstrated that M. alcaliphilum 20Z exhibited a rapid response to osmotic shocks, which resulted in the release of the accumulated ectoine under hyposmotic shocks and the immediate uptake of the previously excreted ectoine during hyperosmotic shocks. A second experiment was carried out under continuous cultivation mode in two sequential stirred tank reactors operated at NaCl concentrations of 0 and 6 %. Cells exhibited a constant intracellular ectoine concentration of 70.4 ± 14.3 mg g biomass -1 along the entire operation period when cultivated at a NaCl concentration of 6%. The centrifugation of the cultivation broth followed by a hyposmotic shock resulted in the excretion of ~ 70 % of the total intracellular ectoine. In brief, this research shows the feasibility of the continuous bioconversion of diluted CH 4 emissions into high added-value products such as ectoine, which can turn greenhouse gas abatement into a sustainable and profitable process.

Metabolic Engineering of Corynebacterium glutamicum for High‐Level Ectoine Production: Design, Combinatorial Assembly, and Implementation of a Transcriptionally Balanced Heterologous Ectoine Pathway

“…In this study, C. glutamicum , a well‐established industrial microbe, was upgraded for the production of ectoine from sugar and molasses. From an industrial perspective, ectoine is a high‐priced molecule (€900 kg −1 ) with a rather small market volume . This market situation prioritizes the key indicators for economic performance in the order titer > productivity > yield.…”

Technologies for the bioconversion of methane into more valuable products

“…For example, systems operated with sugars as a carbon source achieved biomass concentrations up to 30 g L -1 and therefore, higher fermenter productivities. However, pure methanotrophic strains achieved average biomass concentrations of 1.0 g L -1 and bioproduct productivities 10 to 100 times lower depending on the product [20,28,38,39,41,[56][57][58]. In this context, mass transfer limitations during EPS and ectoine production can be even more pronounced as a result of the lower CH4 solubility at higher cultivation broth salinity [59], Nowadays, the process implemented at industrial scale using Halomonas elongate involves the cyclic increase and decrease of the salt concentration in the cultivation broth up to 12 % NaCl, which severely limits O2 mass transport and also triggers reactor corrosion.…”

“…with average contents of 37.4 mg ectoine (g biomass) -1 ) [27], while in 2017 a CH4-based biomilking process resulted in extracellular concentrations of 253.4 ± 55.1 mg L -1 , corresponding to a recovery of ~ 70 % of the total intra-cellular ectoine accumulated [28].…”

“…In this context, mass transfer limitations during EPS and ectoine production can be even more pronounced as a result of the lower CH4 solubility at higher cultivation broth salinity [59], Nowadays, the process implemented at industrial scale using Halomonas elongate involves the cyclic increase and decrease of the salt concentration in the cultivation broth up to 12 % NaCl, which severely limits O2 mass transport and also triggers reactor corrosion. However, recent studies conducted for the production of ectoine with methanotrophs were carried out at an optimum salt concentration of 6 % NaCl, which could eventually limit the above mentioned limitations [28,60]. On the other hand,…”

Novel haloalkaliphilic methanotrophic bacteria: An attempt for enhancing methane bio-refinery

“…Moreover, the use of a consortium instead of a pure strain could be beneficial for industrial ectoines production. In this context, M. alcaliphilum 20 Z typically achieves low average biomass concentrations (1.0 g L -1 ), which results in ectoine productivities and CH 4 removal efficiencies 4 times lower than the ones obtained with other methanotrophic bacteria (CH 4 removal efficiencies of 43 to 67 %) ( Cantera et al, 2017b( Cantera et al, , 2016a. Furthermore, the purer a culture is, the higher are the restrictions to grow under environmental stress factors, while a higher population richness and diversity promotes higher resilience and therefore, better reactor performance and bioproduct recovery (Cabrol et al, 2012).…”