Fermentative α-Humulene Production from Homogenized Grass Clippings as a Growth Medium

Abstract

Green waste, e.g., grass clippings, is currently insufficiently recycled and has untapped potential as a valuable resource. Our aim was to use juice from grass clippings as a growth medium for microorganisms. Herein, we demonstrate the production of the sesquiterpene α-humulene with the versatile organism Cupriavidus necator pKR-hum on a growth medium from grass clippings. The medium was compared with established media in terms of microbial growth and terpene production. C. necator pKR-hum shows a maximum growth rate of 0.43 h−1 in the grass medium and 0.50 h−1 in a lysogeny broth (LB) medium. With the grass medium, 2 mg/L of α-humulene were produced compared to 10 mg/L with the LB medium. By concentrating the grass medium and using a controlled bioreactor in combination with an optimized in situ product removal, comparable product concentrations could likely be achieved. To the best of our knowledge, this is the first time that juice from grass clippings has been used as a growth medium without any further additives for microbial product synthesis. This use of green waste as a material represents a new bioeconomic utilization option of waste materials and could contribute to improving the economics of grass biorefineries.

Municipal green waste as substrate for the microbial production of platform chemicals

“…There are already publications on the use of grass press juice as feedstock for fermentations. Schoeters et al report 6.7 g L −1 of total carbon and 0.5 g L −1 of total nitrogen in press juice from a mixture of Festulolium and perennial ryegrass (Schoeters et al 2023 ), while Langsdorf et al measured 20.0 g L −1 total organic carbon and 1.2 g L −1 total nitrogen in press juice from grass clippings (Langsdorf et al 2022 ).…”

“…For example, Schoeters et al used press juice from a mixture of Festulolium and perennial ryegrass for the co-cultivation of microalgae to produce high-protein biomass (Schoeters et al 2023 ). Langsdorf et al prepared growth media from grass clippings either by using a juice extractor or by blending the feedstock and produced α-humulene with Cupriavidus necator without any further additives (Langsdorf et al 2022 ). The press juices of Miscanthus x giganteus (MxG), Lolium perenne , and grass-clover mixtures were also already used for cultivations (Boakye-Boaten et al 2016 ; Hull et al 2014 ; Santamaria‐Fernandez et al 2019 ).…”

Peroxidases from grass clippings for the removal of phenolic compounds from wastewater

“…Recently, we explained efficient methods for the pretreatment of such materials (Varriale et al, 2022) and demonstrated the use of grass clippings as a substrate for the microbial production of the terpenoid α-humulene (Langsdorf et al, 2022). In continuation of this work, we hypothesized that green waste may also serve as a cost-effective source of enzymes.…”

Autotrophic Production of the Sesquiterpene α-Humulene with Cupriavidus necator in a Controlled Bioreactor

“…By combining water electrolysis with the ability to convert CO 2 , C. necator can also be used in bioelectrochemical synthesis, combining CO 2 conversion with the sustainable generation of electrical energy to produce valuable chemicals [4][5][6]. The ability to convert a wide range of waste streams into these high-value products provides a great opportunity to develop a waste-based circular bioeconomy based on C. necator [7][8][9].…”