Increased Rhamnolipid Concentration and Productivity Achieved with Advanced Process Design

Abstract

Rhamnolipids are biosurfactants having several applications. A major limitation in rhamnolipid production is low productivity, which decreases significantly during stationary-phase production. In this study, fermentations were first made with nitrogen-limited stationary phase. Long-term rhamnolipid production (up to 505 h) could be maintained with low-rate N-source addition but the intermittent cell growth led to lower productivity (q p), particularly apparent at the highest addition rate. Four fermentations were next made under non-N-limited stationary phase without and with N-source supplementation; q p could be much higher at 24-26 mg g −1 h −1. Three final fermentations were designed to build the maximum cell concentration to 30 g L −1 in two growth phases where the growth rate in the second phase was regulated by N-addition to control foaming. Cultures then entered non-N-limited stationary phase and were N-supplemented. At an optimal rate of 15% growth-N per 24 h to maintain cell activity, a highest rhamnolipid concentration of 120 g L −1 was obtained after 144 h with overall productivity of 839 mg L −1 h −1 .

High-quality physiology of Alcanivorax borkumensis SK2 producing glycolipids enables efficient stirred-tank bioreactor cultivation

“…A defined growth medium is essential for secondary metabolite production like biosurfactants, as it allows fed-batch cultivation, where often second substrate limitations or specific carbon-to-nitrogen ratios are used ( Invally and Ju, 2020 ; Merkel et al, 2022 ). In order to establish biosurfactant production, the growth behavior of A. borkumensis SK2 was investigated in the published ONR7a medium ( Dyksterhouse et al, 1995 ) and the modified (mod.)…”

Optimized Feeding Strategies for Biosurfactant Production from Acetate by Alcanivorax borkumensis SK2

“…However, the limitation of enhancement was observed at a C/N ratio of 62 Cmol Nmol −1 with NaNO 3 as the nitrogen source and glycerol as the carbon source, and the limiting C/N ratio was found to depend on the carbon source [32]. Another factor influencing glycolipid production at high C/N ratios was demonstrated by Invally and Ju [72] in their fed-batch fermentation study of P. aeruginosa. They discovered that a steady, small nitrogen feed was essential to maintain cell activity for rhamnolipid production.…”

“…This high nitrogen amount favors the formation of biomass. It is known that secondary metabolites such as biosurfactants are produced more efficiently under nitrogen-starvation or nitrogen-limiting conditions [30,72,73]. Therefore, the process has been further optimized regarding the nitrogen source.…”

DoE-based medium optimization for improved biosurfactant production with Aureobasidium pullulans

“…One group of well-studied glycolipids are rhamnolipids (RLs). Reaching industrial relevant titers of nearly 125 g L −1 , the best characterized RL producer is Pseudomonas aeruginosa ( Invally and Ju, 2020 ), whose human pathogenicity makes industrial use difficult. The recombinant RL producer Pseudomonas putida KT2440 does not have this disadvantage ( Wittgens et al, 2011 ; Tiso et al, 2016 ; Soberón-Chávez et al, 2021 ).…”