Assessing the feasibility and sustainability of a surfactin production process: a techno-economic and environmental analysis

Biosurfactants have been profiled as a sustainable replacement for chemical-based surfactants since these bio-based molecules have higher biodegradability. Few research papers have focused on assessing biosurfactant production to elucidate potential bottlenecks. This research aims to assess the techno-economic and environmental performance of surfactin production in a potential scale of 65m3, considering different product yields and involving the European energy crisis of 2021-2022. The conceptual design, simulation, techno-economic, and environmental assessments were done by applying process engineering concepts and software tools such as Aspen Plus v.9.0 and SimaPro v.8.3.3. The results demonstrated the high economic potential of surfactin production since the higher values in the market offset the low fermentation yields, low recovery efficiency, and high capital investment. The sensitivity analysis of the economic assessment elucidated a minimum surfactin selling price between 29 and 31 USD/kg of surfactin, while a minimum processing scale for economic feasibility between 4 and 5 kg/h is needed to reach an equilibrium point. The environmental performance must be improved since the carbon footprint was 43 kg CO2eq/kg of surfactin. The downstream processing and energy demand are the main bottlenecks since these aspects contribute to 63 and 25% of the total emissions. The fermentation process and downstream process are key factors for future optimization and research.

Evaluation of an external foam column for in situ product removal in aerated surfactin production processes

In Bacillus fermentation processes, severe foam formation may occur in aerated bioreactor systems caused by surface-active lipopeptides. Although they represent interesting compounds for industrial biotechnology, their property of foaming excessively during aeration may pose challenges for bioproduction. One option to turn this obstacle into an advantage is to apply foam fractionation and thus realize in situ product removal as an initial downstream step. Here we present and evaluate a method for integrated foam fractionation. A special feature of this setup is the external foam column that operates separately in terms of, e.g., aeration rates from the bioreactor system and allows recycling of cells and media. This provides additional control points in contrast to an internal foam column or a foam trap. To demonstrate the applicability of this method, the foam column was exemplarily operated during an aerated batch process using the surfactin-producing Bacillus subtilis strain JABs24. It was also investigated how the presence of lipopeptides and bacterial cells affected functionality. As expected, the major foam formation resulted in fermentation difficulties during aerated processes, partially resulting in reactor overflow. However, an overall robust performance of the foam fractionation could be demonstrated. A maximum surfactin concentration of 7.7 g/L in the foamate and enrichments of up to 4 were achieved. It was further observed that high lipopeptide enrichments were associated with low sampling flow rates of the foamate. This relation could be influenced by changing the operating parameters of the foam column. With the methodology presented here, an enrichment of biosurfactants with simultaneous retention of the production cells was possible. Since both process aeration and foam fractionation can be individually controlled and designed, this method offers the prospect of being transferred beyond aerated batch processes.

Lysinibacillus irui sp. nov., isolated from Iru, fermented African locust beans

A Gram-positive, motile, aerobic, rod-shaped, endospore-forming strain designated IRB4-01T was isolated from fermented African locust beans (Iru) obtained from Bodija market in the city of Ibadan, southwestern Nigeria, during a screening process from food-related sources. IRB4-01T grew at 10-50 °C (optimum, 35-37 °C), pH 6-10 (optimum, pH 7) and in 0-6 % NaCl (optimum, 1-3 %). Phylogenetic analyses based on 16S rRNA and combined short- and long-read genome sequencing revealed that IRB4-01T is closely related to Lysinibacillus cavernae SYSU K30005T and Lysinibacillus boronitolerans 10aT. The cell-wall peptidoglycan type was A4α (Lys-Asp), containing the diagnostic diamino acid lysine. The major polar lipids in strain IRB4-01T were diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylglycerol and an unidentified phospholipid, while the predominant menaquinone was MK-7. The major cellular fatty acids were iso-C15 : 0, anteiso-C15 : 0 and iso-C16 : 0. Genomic DNA G+C content was 37.4  mol%, while the digital DNA-DNA hybridization revealed 33.6 and 32.3 % relatedness to L. cavernae SYSU K30005T and L. boronitolerans 10aT, respectively. Based on phenotypic, physiological and chemotaxonomic characteristics, as well as genome comparisons, strain IRB4-01T represents a novel species of the genus Lysinibacillus, for which the name Lysinibacillus irui sp. nov. is proposed. The type strain is IRB4-01T (NCIMB 15452T=LMG 32887T). Hybrid genome data are provided on the NCBI database using the Bioproject number PRJNA906010 and accession numbers CP113527 and CP113528. Additionally, a representative 16S rRNA sequence is available with the GenBank accession number OQ566940.

Design and evaluation of a 3D-printed, lab-scale perfusion bioreactor for novel biotechnological applications

3D-printing increased in significance for biotechnological research as new applications like lab-on-a-chip systems, cell culture devices or 3D-printed foods were uncovered. Besides mammalian cell culture, only few of those applications focus on the cultivation of microorganisms and none of these make use of the advantages of perfusion systems. One example for applying 3D-printing for bioreactor development is the microbial utilization of alternative substrates derived from lignocellulose, where dilute carbon concentrations and harmful substances present a major challenge. Furthermore, quickly manufactured and affordable 3D-printed bioreactors can accelerate early development phases through parallelization. In this work, a novel perfusion bioreactor system consisting of parts manufactured by fused filament fabrication (FFF) is presented and evaluated. Hydrophilic membranes are used for cell retention to allow the application of dilute substrates. Oxygen supply is provided by membrane diffusion via hydrophobic polytetrafluoroethylene membranes. An exemplary cultivation of Corynebacterium glutamicum ATCC 13032 supports the theoretical design by achieving competitive biomass concentrations of 18.4 g L-1 after 52 h. As a proof-of-concept for cultivation of microorganisms in perfusion mode, the described bioreactor system has application potential for bioconversion of multi-component substrate-streams in a lignocellulose-based bioeconomy, for in-situ product removal or design considerations of future applications for tissue cultures. Furthermore, this work provides a template-based toolbox with instructions for creating reference systems in different application scenarios or tailor-made bioreactor systems.

Characterization ofantifungal properties of lipopeptide-producing Bacillus velezensis strains and their proteome-based response to the phytopathogens, Diaporthe spp

Introduction: B. velezensis strains are of interest in agricultural applications due to their beneficial interactions with plants, notable through their antimicrobial activity. The biocontrol ability of two new lipopeptides-producing B. velezensis strains ES1-02 and EFSO2-04, against fungal phytopathogens of Diaporthe spp., was evaluated and compared with reference strains QST713 and FZB42. All strains were found to be effective against the plant pathogens, with the new strains showing comparable antifungal activity to QST713 and slightly lower activity than FZB42. Methods: Lipopeptides and their isoforms were identified by high-performance thin-layer chromatography (HPTLC) and mass spectrometric measurements. The associated antifungal influences were determined in direct in vitro antagonistic dual culture assays, and the inhibitory growth effects on Diaporthe spp. as representatives of phytopathogenic fungi were determined. The effects on bacterial physiology of selected B. velezensis strains were analyzed by mass spectrometric proteomic analyses using nano-LC-MS/MS. Results and Discussion: Lipopeptide production analysis revealed that all strains produced surfactin, and one lipopeptide of the iturin family, including bacillomycin L by ES1-02 and EFSO2-04, while QST713 and FZB42 produced iturin A and bacillomycin D, respectively. Fengycin production was however only detected in the reference strains. As a result of co-incubation of strain ES1-02 with the antagonistic phytopathogen D. longicolla, an increase in surfactin production of up to 10-fold was observed, making stress induction due to competitors an attractive strategy for surfactin bioproduction. An associated global proteome analysis showed a more detailed overview about the adaptation and response mechanisms of B. velezensis, including an increased abundance of proteins associated with the biosynthesis of antimicrobial compounds. Furthermore, higher abundance was determined for proteins associated with oxidative, nitrosative, and general stress response. In contrast, proteins involved in phosphate uptake, amino acid transport, and translation were decreased in abundance. Altogether, this study provides new insights into the physiological adaptation of lipopeptide-producing B. velezensis strains, which show the potential for use as biocontrol agents with respect to phytopathogenic fungi.

Deletion of Rap-phosphatases for quorum sensing control in Bacillus and its effect on surfactin production

The complex regulatory network in Bacillus, known as quorum sensing, offers many opportunities to modify bacterial gene expression and hence to control bioprocesses. One target regulated by this mechanism is the activity of the P_srfA promoter, which is engaged in the formation of lipopeptide surfactin. It was hypothesised that deletion of rapC, rapF and rapH, encoding for prominent Rap-phosphatases known to affect P_srfA activity, would enhance surfactin production. Therefore, these genes were deleted in a sfp⁺ derivative of B. subtilis 168 with subsequent evaluation of quantitative data. Up to the maximum product formation of the reference strain B. subtilis KM1016 after 16 h of cultivation, the titers of the rap deletion mutants did not exceed the reference. However, an increase in both product yield per biomass Y_P/X and specific surfactin productivity q_surfactin was observed, without any considerable effect on the ComX activity. By extending the cultivation time, a 2.7-fold increase in surfactin titer was observed after 24 h for strain CT10 (ΔrapC) and a 2.5-fold increase for CT11 (ΔrapF) compared to the reference strain KM1016. In addition, Y_P/X was again increased for strains CT10 and CT11, with values of 1.33 g/g and 1.13 g/g, respectively. Interestingly, the effect on surfactin titer in strain CT12 (ΔrapH) was not as distinct, although it achieved the highest promoter activity (P_srfA-lacZ). The data presented support the possibility of involving the quorum sensing system of Bacillus in bioprocess control as shown here on the example of lipopeptide production.

Characterization of Bacillus velezensis UTB96, Demonstrating Improved Lipopeptide Production Compared to the Strain B. velezensis FZB42

Bacillus strains can produce various lipopeptides, known for their antifungal properties. This makes them attractive metabolites for applications in agriculture. Therefore, identification of productive wild-type strains is essential for the development of biopesticides. Bacillus velezensis FZB42 is a well-established strain for biocontrol of plant pathogens in agriculture. Here, we characterized an alternative strain, B. velezensis UTB96, that can produce higher amounts of all three major lipopeptide families, namely surfactin, fengycin, and iturin. UTB96 produces iturin A. Furthermore, UTB96 showed superior antifungal activity towards the soybean fungal pathogen Diaporthe longicolla compared to FZB42. Moreover, the additional provision of different amino acids for lipopeptide production in UTB96 was investigated. Lysine and alanine had stimulatory effects on the production of all three lipopeptide families, while supplementation of leucine, valine and isoleucine decreased the lipopeptide bioproduction. Using a 45-litre bioreactor system for upscaling in batch culture, lipopeptide titers of about 140 mg/L surfactin, 620 mg/L iturin A, and 45 mg/L fengycin were achieved. In conclusion, it becomes clear that B. velezensis UTB96 is a promising strain for further research application in the field of agricultural biological controls of fungal diseases.

High-level recombinant protein production with Corynebacterium glutamicum using acetate as carbon source

In recent years, biotechnological conversion of the alternative carbon source acetate has attracted much attention. So far, acetate has been mainly used for microbial production of bioproducts with bulk applications. In this study, we aimed to investigate the potential of acetate as carbon source for heterologous protein production using the acetate-utilizing platform organism Corynebacterium glutamicum. For this purpose, expression of model protein eYFP with the promoter systems T7lac and tac was characterized during growth of C. glutamicum on acetate as sole carbon source. The results indicated a 3.3-fold higher fluorescence level for acetate-based eYFP production with T7 expression strain MB001(DE3) pMKEx2-eyfp compared to MB001 pEKEx2-eyfp. Interestingly, comparative eyfp expression studies on acetate or glucose revealed an up to 83% higher biomass-specific production for T7 RNAP-dependent eYFP production using acetate as carbon source. Furthermore, high-level protein accumulation on acetate was demonstrated for the first time in a high cell density cultivation process with pH-coupled online feeding control, resulting in a final protein titer of 2.7 g/L and product yield of 4 g per 100 g cell dry weight. This study presents a first proof of concept for efficient microbial upgrading of potentially low-cost acetate into high-value bioproducts, such as recombinant proteins.

A Polyclonal Selex Aptamer Library Directly Allows Specific Labelling of the Human Gut Bacterium Blautia producta without Isolating Individual Aptamers

Recent studies have demonstrated that changes in the abundance of the intestinal bacterium Blautia producta, a potential probiotic, are closely associated with the development of various diseases such as obesity, diabetes, some neurodegenerative diseases, and certain cancers. However, there is still a lack of an effective method to detect the abundance of B. producta in the gut rapidly. Especially, DNA aptamers are now widely used as biometric components for medical testing due to their unique characteristics, including high chemical stability, low production cost, ease of chemical modification, low immunogenicity, and fast reproducibility. We successfully obtained a high-affinity nucleic acid aptamer library (B.p-R14) after 14 SELEX rounds, which efficiently discriminates B. producta in different analysis techniques including fluorometric suspension assays or fluorescence microscopy from other major gut bacteria in complex mixtures and even in human stool samples. These preliminary findings will be the basis towards aptamer-based biosensing applications for the fast and reliable monitoring of B. producta in the human gut microbiome.

Acetate-based production of itaconic acid with Corynebacterium glutamicum using an integrated pH-coupled feeding control

To date, most bio-based products of industrial biotechnology stem from sugar-based carbon sources originating from food and feed competing resources. Exemplary for bioproducts converted from glucose, the potential C5 platform chemical itaconic acid is presently produced by the filamentous fungus Aspergillus terreus. Here, an engineered strain of the industrial platform organism Corynebacterium glutamicum ATCC 13032 was used for acetate-based production of itaconic acid to overcome current production difficulties. For this purpose, C. glutamicum ICD^R453C (pEKEx2-malEcad_opt) with a mutated icd variant for reduced isocitrate dehydrogenase activity was constructed harbouring pEKEx2-malEcad_opt, that includes a cis-aconitate dehydrogenase gene originating from A. terreus. Overall, a peak volumetric productivity of 1.01 gL^-1h^-1 was achieved resulting in an itaconate titer of 29.2 g/L, by using an integrated pH-coupled acetate feeding control in a fed-batch process without base titration. The results support the high potential of acetate as alternative substrate for bioproduction.

Exploration of surfactin production by newly isolated Bacillus and Lysinibacillus strains from food related sources

As a lipopeptide (LP), surfactin exhibits properties, such as emulsifying and dispersing ability, which are useful in food industry. Discovery of new LP-producing strains from food sources is an important step towards possible application of surfactin in foods. A total of 211 spore-forming, Gram-positive, and catalase-positive bacterial strains were isolated from fermented African locust beans (iru) and Palm Oil Mill Effluents in a screening process and examined for their ability to produce surfactin. This was achieved by a combination of methods, which included microbiological and molecular classification of strains, along with chemical analysis of surfactin production. Altogether, 29 isolates, positive for oil spreading and emulsification assays, were further identified with 16S rDNA analysis. The strains belonged to nine species including less commonly reported strains of Lysinibacillus, Bacillus flexus, B. tequilensis, and B. aryabhattai. The surfactin production was quantitatively and qualitatively analyzed by high-performance thin-layer chromatography (HPTLC) and liquid chromatography-mass spectrometry (LC-MS). Confirmation of surfactin by MS was achieved in all the 29 strains. Highest surfactin production capability was found in B. subtilis IRB2-A1 with a titer of 1444.1 mg L^-1 .

High cell density cultivation of Corynebacterium glutamicum on bio-based lignocellulosic acetate using pH-coupled online feeding control

Acetate represents a promising alternative carbon source for future industrial biotechnology. In this study, the high potential of Corynebacterium glutamicum for utilizing acetate as sole carbon source was demonstrated. Batch culture studies revealed that C. glutamicum ATCC 13032 naturally exhibits high acetate tolerance with maximum growth rates (µ_max = 0.47 h^-1) similar to those on D-glucose. Based on a simple and auto-regulated pH-coupled feeding strategy which utilizes bio-acetic acid in pure form, a novel and high-efficient fed-batch process was developed in a 42 L stirred-tank bioreactor. By optimizing the carbon-to-nitrogen (C/N) feeding ratio, maximum biomass concentrations of 80.2 g_CDW/L were achieved with a space-time yield of 66.6 g_CDW/L·d. In addition, a process model was implemented describing the time-courses of biomass growth and substrate concentrations. This is the first study in which an industrial platform organism was grown to high cell densities using green, lignocellulosic acetate as an alternative carbon source.

Modeling the time course of ComX: towards molecular process control for Bacillus wild-type cultivations

Wild-type cultivations are of invaluable relevance for industrial biotechnology when it comes to the agricultural or food sector. Here, genetic engineering is hardly applicable due to legal barriers and consumer’s demand for GMO-free products. An important pillar for wild-type cultivations displays the genus Bacillus. One of the challenges for Bacillus cultivations is the global ComX-dependent quorum sensing system. Here, molecular process control can serve as a tool to optimize the production process without genetic engineering. To realize this approach, quantitative knowledge of the mechanism is essential, which, however, is often available only to a limited extent. The presented work provides a case study based on the production of cyclic lipopeptide surfactin, whose expression is in dependence of ComX, using natural producer B. subtilis DSM 10 ^T. First, a surfactin reference process with 40 g/L of glucose was performed as batch fermentation in a pilot scale bioreactor system to gain novel insights into kinetic behavior of ComX in relation to surfactin production. Interestingly, the specific surfactin productivity did not increase linearly with ComX activity. The data were then used to derive a mathematic model for the time course of ComX in dependence of existing biomass, biomass growth as well as a putative ComX-specific protease. The newly adapted model was validated and transferred to other batch fermentations, employing 20 and 60 g/L glucose. The applied approach can serve as a model system for molecular process control strategies, which can thus be extended to other quorum sensing dependent wild-type cultivations.

Expression of degQ gene and its effect on lipopeptide production as well as formation of secretory proteases in Bacillus subtilis strains

Bacillus subtilis is described as a promising production strain for lipopeptides. In the case of B. subtilis strains JABs24 and DSM10T , surfactin and plipastatin are produced. Lipopeptide formation is controlled, among others, by the DegU response regulator. The activating phospho-transfer by the DegS sensor kinase is stimulated by the pleiotropic regulator DegQ, resulting in enhanced DegU activation. In B. subtilis 168, a point mutation in the degQ promoter region leads to a reduction in gene expression. Corresponding reporter strains showed a 14-fold reduced expression. This effect on degQ expression and the associated impact on lipopeptide formation was examined for B. subtilis JABs24, a lipopeptide-producing derivative of strain 168, and B. subtilis wild-type strain DSM10T , which has a native degQ expression. Based on the stimulatory effects of the DegU regulator on secretory protease formation, the impact of degQ expression on extracellular protease activity was additionally investigated. To follow the impact of degQ, a deletion mutant was constructed for DSM10T , while a natively expressed degQ version was integrated into strain JABs24. This allowed strain-specific quantification of the stimulatory effect of degQ expression on plipastatin and the negative effect on surfactin production in strains JABs24 and DSM10T . While an unaffected degQ expression reduced surfactin production in JABs24 by about 25%, a sixfold increase in plipastatin was observed. In contrast, degQ deletion in DSM10T increased surfactin titer by threefold but decreased plipastatin production by fivefold. In addition, although significant differences in extracellular protease activity were detected, no decrease in plipastatin and surfactin produced during cultivation was observed.

Influence of B. subtilis 3NA mutations in spo0A and abrB on surfactin production in B. subtilis 168

Background

Bacillus subtilis is a well-established host for a variety of bioproduction processes, with much interest focused on the production of biosurfactants such as the cyclic lipopeptide surfactin. Surfactin production is tightly intertwined with quorum sensing and regulatory cell differentiation processes. As previous studies have shown, a non-sporulating B. subtilis strain 3NA encoding a functional sfp locus but mutations in the spo0A and abrB loci, called JABs32, exhibits noticeably increased surfactin production capabilities. In this work, the impacts of introducing JABs32 mutations in the genes spo0A, abrB and abh from 3NA into strain KM1016, a surfactin-forming derivative of B. subtilis 168, was investigated. This study aims to show these mutations are responsible for the surfactin producing performance of strain JABs32 in fed-batch bioreactor cultivations.

Results

Single and double mutant strains of B. subtilis KM1016 were constructed encoding gene deletions of spo0A, abrB and homologous abh. Furthermore, an elongated abrB version, called abrB*, as described for JABs32 was integrated. Single and combinatory mutant strains were analysed in respect of growth behaviour, native P_srfA promoter expression and surfactin production. Deletion of spo0A led to increased growth rates with lowered surfactin titers, while deletion or elongation of abrB resulted in lowered growth rates and high surfactin yields, compared to KM1016. The double mutant strains B. subtilis KM1036 and KM1020 encoding Δspo0A abrB* and Δspo0A ΔabrB were compared to reference strain JABs32, with KM1036 exhibiting similar production parameters and impeded cell growth and surfactin production for KM1020. Bioreactor fed-batch cultivations comparing a Δspo0A abrB* mutant of KM1016, KM681, with JABs32 showed a decrease of 32% in surfactin concentration.

Conclusions

The genetic differences of B. subtilis KM1016 and JABs32 give rise to new and improved fermentation methods through high cell density processes. Deletion of the spo0A locus was shown to be the reason for higher biomass concentrations. Only in combination with an elongation of abrB was this strain able to reach high surfactin titers of 18.27 g L⁻¹ in fed-batch cultivations. This work shows, that a B. subtilis strain can be turned into a high cell density surfactin production strain by introduction of two mutations.

Exploiting RNA thermometer-driven molecular bioprocess control as a concept for heterologous rhamnolipid production

A key challenge to advance the efficiency of bioprocesses is the uncoupling of biomass from product formation, as biomass represents a by-product that is in most cases difficult to recycle efficiently. Using the example of rhamnolipid biosurfactants, a temperature-sensitive heterologous production system under translation control of a fourU RNA thermometer from Salmonella was established to allow separating phases of preferred growth from product formation. Rhamnolipids as bulk chemicals represent a model system for future processes of industrial biotechnology and are therefore tied to the efficiency requirements in competition with the chemical industry. Experimental data confirms function of the RNA thermometer and suggests a major effect of temperature on specific rhamnolipid production rates with an increase of the average production rate by a factor of 11 between 25 and 38 °C, while the major part of this increase is attributable to the regulatory effect of the RNA thermometer rather than an unspecific overall increase in bacterial metabolism. The production capacity of the developed temperature sensitive-system was evaluated in a simple batch process driven by a temperature switch. Product formation was evaluated by efficiency parameters and yields, confirming increased product formation rates and product-per-biomass yields compared to a high titer heterologous rhamnolipid production process from literature.

Bacillus subtilis High Cell Density Fermentation Using a Sporulation-Deficient Strain for the Production of Surfactin

Abstract

Bacillus subtilis 3NA is a strain capable of reaching high cell densities. A surfactin producing sfp⁺ variant of this strain, named JABs32, was utilized in fed-batch cultivation processes. Both a glucose and an ammonia solution were fed to set a steady growth rate μ of 0.1 h^-1. In this process, a cell dry weight of up to 88 g L^-1 was reached after 38 h of cultivation, and surfactin titers of up to 26.5 g L^-1 were detected in this high cell density fermentation process, achieving a Y_P/X value of 0.23 g g^-1 as well as a q_P/X of 0.007 g g^-1 h^-1. In sum, a 21-fold increase in surfactin titer was obtained compared with cultivations in shake flasks. In contrast to fed-batch operations using Bacillus subtilis JABs24, an sfp⁺ variant derived from B. subtilis 168, JABs32, reached an up to fourfold increase in surfactin titers using the same fed-batch protocol. Additionally, a two-stage feed process was established utilizing strain JABs32. Using an optimized mineral salt medium in this high cell density fermentation approach, after 31 h of cultivation, surfactin titers of 23.7 g L^-1 were reached with a biomass concentration of 41.3 g L^-1, thus achieving an enhanced Y_P/X value of 0.57 g g^-1 as well as a q_P/X of 0.018 g g^-1 h^-1. The mutation of spo0A locus and an elongation of AbrB in the strain utilized in combination with a high cell density fed-batch process represents a promising new route for future enhancements on surfactin production.

Key points

• Utilization of a sporulation deficient strain for fed-batch operations

• High cell density process with Bacillus subtilis for lipopeptide production was established

• High titer surfactin production capabilities confirm highly promising future platform strain

Evaluation of an oxygen-dependent self-inducible surfactin synthesis in B. subtilis by substitution of native promoter PsrfA by anaerobically active PnarG and PnasD

A novel approach targeting self-inducible surfactin synthesis under oxygen-limited conditions is presented. Because both the nitrate (NarGHI) and nitrite (NasDE) reductase are highly expressed during anaerobic growth of B. subtilis, the native promoter PsrfA of the surfactin operon in strain B. subtilis JABs24 was replaced by promoters PnarG and PnasD to induce surfactin synthesis anaerobically. Shake flask cultivations with varying oxygen availabilities indicated no significant differences in native PsrfA expression. As hypothesized, activity of PnarG and PnasD increased with lower oxygen levels and surfactin was not produced by PsrfA::PnarG as well as PsrfA::PnasD mutant strains under conditions with highest oxygen availability. PnarG showed expressions similar to PsrfA at lowest oxygen availability, while maximum value of PnasD was more than 5.5-fold higher. Although the promoter exchange PsrfA::PnarG resulted in a decreased surfactin titer at lowest oxygen availability, the strain carrying PsrfA::PnasD reached a 1.4-fold increased surfactin concentration with 696 mg/L and revealed an exceptional high overall YP/X of 1.007 g/g. This value also surpassed the YP/X of the reference strain JABs24 at highest and moderate oxygen availability. Bioreactor cultivations illustrated that significant cell lysis occurred when the process of "anaerobization" was performed too fast. However, processes with a constantly low agitation and aeration rate showed promising potential for process improvement, especially by employing the strain carrying PsrfA::PnasD promoter exchange. Additionally, replacement of other native promoters by nitrite reductase promoter PnasD represents a promising tool for anaerobic-inducible bioprocesses in Bacillus.

Towards the Anaerobic Production of Surfactin Using Bacillus subtilis

The anaerobic growth of B. subtilis to synthesize surfactin poses an alternative strategy to conventional aerobic cultivations. In general, the strong foam formation observed during aerobic processes represents a major obstacle. Anaerobic processes have, amongst others, the distinct advantage that the total bioreactor volume can be exploited as foaming does not occur. Recent studies also reported on promising product per biomass yields. However, anaerobic growth in comparison to aerobic processes has several disadvantages. For example, the overall titers are comparably low and cultivations are time-consuming due to low growth rates. B. subtilis JABs24, a derivate of strain 168 with the ability to synthesize surfactin, was used as model strain in this study. Ammonium and nitrite were hypothesized to negatively influence anaerobic growth. Ammonium with initial concentrations up to 0.2 mol/L was shown to have no significant impact on growth, but increasing concentrations resulted in decreased surfactin titers and reduced nitrate reductase expression. Anaerobic cultivations spiked with increasing nitrite concentrations resulted in prolonged lag-phases. Indeed, growth rates were in a similar range after the lag-phase indicating that nitrite has a neglectable effect on the observed decreasing growth rates. In bioreactor cultivations, the specific growth rate decreased with increasing glucose concentrations during the time course of both batch and fed-batch processes to less than 0.05 1/h. In addition, surfactin titers, overall Y _P/X and Y _P/S were 53%, ∼42%, and ∼57% lower than in serum flask with 0.190 g/L, 0.344 g/g and 0.015 g/g. The Y _X/S, on the contrary, was 30% lower in the serum flask with 0.044 g/g. The productivities q were similar with ∼0.005 g/(g⋅h). However, acetate strongly accumulated during cultivation and was posed as further metabolite that might negatively influence anaerobic growth. Acetate added to anaerobic cultivations in a range from 0 g/L up to 10 g/L resulted in a reduced maximum and overall growth rate μ by 44% and 30%, respectively. To conclude, acetate was identified as a promising target for future process enhancement and strain engineering. Though, the current study demonstrates that the anaerobic cultivation to synthesize surfactin represents a reasonable perspective and feasible alternative to conventional processes.

Development of a Bioprocess for the Production of Cyclic Lipopeptides Pseudofactins With Efficient Purification From Collected Foam

Microbial surfactants (biosurfactants) have gained interest as promising substitutes of synthetic surface-active compounds. However, their production and purification are still challenging, with significant room for efficiency and costs optimization. In this work, we introduce a method for the enhanced production and purification of cyclic lipopeptides pseudofactins (PFs) from Pseudomonas fluorescens BD5 cultures. The method is directly applicable in a technical scale with the possibility of further upscaling. Comparing to the original protocol for production of PFs (cultures in mineral salt medium in shaken flasks followed by solvent-solvent extraction of PFs), our process offers not only ∼24-fold increased productivity, but also easier and more efficient purification. The new process combines high yield of PFs (∼7.2 grams of PFs per 30 L of working volume), with recovery levels of 80–90% and purity of raw PFs up to 60–70%. These were achieved with an innovative, single-step thermal co-precipitation and extraction of PFs directly from collected foam, as a large amount of PF-enriched foam was produced during the bioprocess. Besides we present a protocol for the selective production of PF structural analogs and their separation with high-performance liquid chromatography. Our approach can be potentially utilized in the efficient production and purification of other lipopeptides of Pseudomonas and Bacillus origin.

Construction and description of a constitutive plipastatin mono-producing Bacillus subtilis

BACKGROUND

Plipastatin is a potent Bacillus antimicrobial lipopeptide with the prospect to replace conventional antifungal chemicals for controlling plant pathogens. However, the application of this lipopeptide has so far been investigated in a few cases, principally because of the yield in low concentration and unknown regulation of biosynthesis pathways. B. subtilis synthesizes plipastatin by a non-ribosomal peptide synthetase encoded by the ppsABCDE operon. In this study, B. subtilis 3NA (a non-sporulation strain) was engineered to gain more insights about plipastatin mono-production.

RESULTS

The 4-phosphopantetheinyl transferase Sfp posttranslationally converts non-ribosomal peptide synthetases from inactive apoforms into their active holoforms. In case of 3NA strain, sfp gene is inactive. Accordingly, the first step was an integration of a repaired sfp version in 3NA to construct strain BMV9. Subsequently, plipastatin production was doubled after integration of a fully expressed degQ version from B. subtilis DSM10^T strain (strain BMV10), ensuring stimulation of DegU-P regulatory pathway that positively controls the ppsABSDE operon. Moreover, markerless substitution of the comparably weak native plipastatin promoter (P_pps) against the strong constitutive promoter P_veg led to approximately fivefold enhancement of plipastatin production in BMV11 compared to BMV9. Intriguingly, combination of both repaired degQ expression and promoter exchange (P_pps::P_veg) did not increase the plipastatin yield. Afterwards, deletion of surfactin (srfAA-AD) operon by the retaining the regulatory comS which is located within srfAB and is involved in natural competence development, resulted in the loss of plipastatin production in BMV9 and significantly decreased the plipastatin production of BMV11. We also observed that supplementation of ornithine as a precursor for plipastatin formation caused higher production of plipastatin in mono-producer strains, albeit with a modified pattern of plipastatin composition.

CONCLUSIONS

This study provides evidence that degQ stimulates the native plipastatin production. Moreover, a full plipastatin production requires surfactin synthetase or some of its components. Furthermore, as another conclusion of this study, results point towards ornithine provision being an indispensable constituent for a plipastatin mono-producer B. subtilis strain. Therefore, targeting the ornithine metabolic flux might be a promising strategy to further investigate and enhance plipastatin production by B. subtilis plipastatin mono-producer strains.

History and Evolution of Modeling in Biotechnology: Modeling & Simulation, Application and Hardware Performance

Biological systems are typically composed of highly interconnected subunits and possess an inherent complexity that make monitoring, control and optimization of a bioprocess a challenging task. Today a toolset of modeling techniques can provide guidance in understanding complexity and in meeting those challenges. Over the last four decades, computational performance increased exponentially. This increase in hardware capacity allowed ever more detailed and computationally intensive models approaching a “one-to-one” representation of the biological reality. Fueled by governmental guidelines like the PAT initiative of the FDA, novel soft sensors and techniques were developed in the past to ensure product quality and provide data in real time. The estimation of current process state and prediction of future process course eventually enabled dynamic process control. In this review, past, present and envisioned future of models in biotechnology are compared and discussed with regard to application in process monitoring, control and optimization. In addition, hardware requirements and availability to fit the needs of increasingly more complex models are summarized. The major techniques and diverse approaches of modeling in industrial biotechnology are compared, and current as well as future trends and perspectives are outlined.

From Acetate to Bio-Based Products: Underexploited Potential for Industrial Biotechnology

Currently, most biotechnological products are based on microbial conversion of carbohydrate substrates that are predominantly generated from sugar- or starch-containing plants. However, direct competitive uses of these feedstocks in the food and feed industry represent a dilemma, so using alternative carbon sources has become increasingly important in industrial biotechnology. A promising alternative carbon source that may be generated in substantial amounts from lignocellulosic biomass and C1 gases is acetate. This review discusses the underexploited potential of acetate to become a next-generation platform substrate in future industrial biotechnology and summarizes alternative sources and routes for acetate production. Furthermore, biotechnological aspects of microbial acetate utilization and the state of the art of biotechnological acetate conversion into value-added bioproducts are highlighted.

Assessment of Bone and Muscle Measurements by Peripheral Quantitative Computed Tomography in Geriatric Patients

The loss of bone and muscle mass increases the risk of osteoporotic fractures. Dual energy X-ray absorptiometry (DXA) loses sensitivity in older age. The purpose of this study was to evaluate bone and muscle measurements of peripheral quantitative computed tomography (pQCT) in a geriatric cohort with osteoporosis. Bone mineral density and muscle area of 168 patients aged 65 years and older (76.3 ± 6.5) were measured with pQCT at distal forearm additionally to an osteoporosis assessment consisting of anamnesis, blood test and DXA of lumbar spine and hip. Prior fractures were categorized in minor and major osteoporotic fractures. Logistic regression was used to show the association of bone mineral density and muscle area with major fractures. 54.8% of the participants had at least one major fracture. Bone mineral density measured with pQCT and muscle area were significantly associated with these fractures (total and trabecular bone mineral density OR 2.243 and 2.195, p < 0.01; muscle area OR 2.378, p < 0.05), whereas DXA bone mineral density showed no significant association. These associations remained after adjustment for age, sex, BMI, physical activity and other factors. In all models for patients >75 years only muscle area was significantly associated (OR 5.354, p < 0.05) with major fractures. Measurement of bone mineral density and muscle area with pQCT seems to have advantage over DXA in fracture association in geriatric patients. Measuring muscle area also adds useful information to estimate the presence of osteosarcopenia.

Evaluating temperature-induced regulation of a ROSE-like RNA-thermometer for heterologous rhamnolipid production in Pseudomonas putida KT2440

The microbial production of rhamnolipids has been in the focus of research for the last decades. Today, mainly heterologous production systems are targeted due to the advantage of non-pathogenic hosts as well as uncoupling from complex quorum sensing regulatory networks compared to their natural producer Pseudomonas aeruginosa. In the recent past, the presence and function of a ROSE-like RNA-thermometer located in the 5′UTR of the rhamnosyltransferase genes rhlAB has been reported in wild type P. aeruginosa. In this study, the temperature-induced regulation of this native RNA-thermometer for heterologous rhamnolipid production was evaluated and its potential application for process control is discussed. For this purpose, the non-pathogenic production host P. putida KT2440 containing the rhlAB genes with the native P. aeruginosa 5′-UTR region was used. The system was evaluated and characterized regarding the effect of temperature on growth and product formation, as represented by efficiency parameters and yields. Experimental data suggests a major effect of temperature on specific rhamnolipid production rates. With maximum values of 0.23 g/(g h) at 37 °C, this constitutes a more than 60% increase compared to the production rate of 0.14 g/(g h) at the growth optimum of 30 °C. Interestingly however, control experiments unveiled that besides the regulatory effect of the RNA-thermometer, multiple metabolic effects may contribute equally to the observed increase in production rate. As such, this work constitutes an important step towards the utilization of temperature-based process designs and enables the possibility for novel approaches for process control.

Surfactin and fengycin contribute to the protection of a Bacillus subtilis strain against grape downy mildew by both direct effect and defence stimulation

Bacillus subtilis GLB191 (hereafter GLB191) is an efficient biological control agent against the biotrophic oomycete Plasmopara viticola, the causal agent of grapevine downy mildew. In this study, we show that GLB191 supernatant is also highly active against downy mildew and that the activity results from both direct effect against the pathogen and stimulation of the plant defences (induction of defence gene expression and callose production). High-performance thin-layer chromatography analysis revealed the presence of the cyclic lipopeptides fengycin and surfactin in the supernatant. Mutants affected in the production of fengycin and/or surfactin were thus obtained and allowed us to show that both surfactin and fengycin contribute to the double activity of GLB191 supernatant against downy mildew. Altogether, this study suggests that GLB191 supernatant could be used as a new biocontrol product against grapevine downy mildew.

Evaluation of surfactin synthesis in a genome reduced Bacillus subtilis strain

Strain engineering is often a method of choice towards increasing the yields of the biosurfactant surfactin which is naturally synthesized by many Bacillus spp., most notably Bacillus subtilis. In the current study, a genome reduced B. subtilis 168 strain lacking 10% of the genome was established and tested for its suitability to synthesize surfactin under aerobic and anaerobic conditions at 25 °C, 30 °C, 37 °C and 40 °C. This genome reduced strain was named IIG-Bs20-5-1 and lacks, amongst others, genes synthesizing the lipopeptide plipastatin, the antibiotic bacilysin, toxins and prophages, as well as genes involved in sporulation. Amongst all temperatures tested, 37 °C was overall superior. In comparison to the reference strain JABs24, a surfactin synthesizing variant of B. subtilis 168, strain IIG-Bs20-5-1 was both aerobically and anaerobically superior with respect to specific growth rates µ and yields Y_X/S. However, in terms of surfactin production, strain JABs24 reached higher absolute concentrations with up to 1147.03 mg/L and 296.37 mg/L under aerobic and anaerobic conditions, respectively. Concomitant, strain JABs24 reached higher Y_P/S and Y_P/X. Here, an outstanding Y_P/X of 1.541 g/g was obtained under anaerobic conditions at 37 °C. The current study indicates that the employed genome reduced strain IIG-Bs20-5-1 has several advantages over the strain JABs24 such as better conversion from glucose into biomass and higher growth rates. However, regarding surfactin synthesis and yields, the strain was overall inferior at the investigated temperatures and oxygen conditions. Further studies addressing process development and strain engineering should be performed combining the current observed advantages of the genome reduced strain to increase the surfactin yields and to construct a tailor-made genome reduced strain to realize the theoretically expected advantages of such genome reduced strains.

Heterologous rhamnolipid biosynthesis by P. putida KT2440 on bio-oil derived small organic acids and fractions

In many cases in industrial biotechnology, substrate costs make up a major part of the overall production costs. One strategy to achieve more cost-efficient processes in general is to exploit cheaper sources of substrate. Small organic acids derived from fast pyrolysis of lignocellulosic biomass represent a significant proportion of microbially accessible carbon in bio-oil. However, using bio-oil for microbial cultivation is a highly challenging task due to its strong adverse effects on microbial growth as well as its complex composition. In this study, the suitability of bio-oil as a substrate for industrial biotechnology was investigated with special focus on organic acids. For this purpose, using the example of the genetically engineered, non-pathogenic bacterium Pseudomonas putida KT2440 producing mono-rhamnolipids, cultivation on small organic acids derived from fast pyrolysis of lignocellulosic biomass, as well as on bio-oil fractions, was investigated and evaluated. As biosurfactants, rhamnolipids represent a potential bulk product of industrial biotechnology where substitution of traditional carbon sources is of conceivable interest. Results suggest that maximum achievable productivities as well as substrate-to-biomass yields are in a comparable range for glucose, acetate, as well as the mixture of acetate, formate and propionate. Similar yields were obtained for a pretreated bio-oil fraction, which was used as reference real raw material, although with significantly lower titers. As such, the reported process constitutes a proof-of-principle for using bio-oil as a potential cost-effective alternative carbon source in a future bio-based economy.

A new multi-channel Mach probe measuring the radial ion flow velocity profile in the boundary plasma of the W7-X stellarator

Ion flow velocity measurement in the edge and scraper-off layer region is beneficial to understand the confinement related phenomenon in fusion devices such as impurity transport and plays an important role in impurity control. During the Wendelstein 7-X (W7-X) operation phase 1.2a, a multi-channel (MC) Mach probe mounted on the multi-purpose manipulator has been used to measure radial profiles of edge ion flow velocity. This MC-Mach probe consists of two polar and two radial arrays of directional Langmuir pins (28 pins in total) serving for different aims, of which the polar arrays could obtain a polar distribution of ion saturation current, while the radial arrays can be used to study the dynamic process of a radially propagated event. In this paper, we report the observation of the radially outward propagation of a low frequency mode with a speed of around 200 m/s. The first measurement of the radial ion flow velocity profile using the MC-Mach probe in the boundary plasma of the W7-X with an island divertor will also be presented.

Time-course and degradation rate of membrane scaffold protein (MSP1D1) during recombinant production

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Relevant efficiency parameters, productivities and production rates for recombinant MSP1D1 are presented for the first time.

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Time-course of MSP1D1 concentration was quantified post-induction in comparison to a reference protein.

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Calculation of specific production rates confirm that degradation is the reason for decreased yields during MSP1D1 expression.

Membrane scaffold proteins (MSPs) are synthetic derivatives of apolipoprotein A-I, a major protein component of human high-density lipoprotein complexes. The most common among these is the variant MSP1D1, which has been in the focus of research on membrane mimetics in the past. As such, the amphipathic MSP1D1 has the ability to self-assemble in the presence of synthetic phospholipids into discoidal nanoparticles, so called nanodiscs. The recombinant production of MSP is exclusively reported using a standard laboratory expression system of the pET family. However, strong variations in both yield and achieved concentration as well as complications related to unspecific degradation are commonly reported. In addition, the time-course of recombinant protein as well as specific protein yields have not yet been quantified conclusively. In this study, the time-course of MSP1D1 concentration was investigated in a standard pET expression system in terms of quantification of production and degradation rates in comparison to a reference protein (eGFP).

Self-assembly of nanoscale particles with biosurfactants and membrane scaffold proteins

Nanodiscs are membrane mimetics which may be used as tools for biochemical and biophysical studies of a variety of membrane proteins. These nanoscale structures are composed of a phospholipid bilayer held together by an amphipathic membrane scaffold protein (MSP). In the past, nanodiscs were successfully assembled with membrane scaffold protein 1D1 and 1,2-dipalmitoyl-sn-glycero-3-phosphorylcholine with a homogeneous diameter of ∼10 nm. In this study, the formation of nanoscale particles from MSP1D1 and rhamnolipid biosurfactants is investigated. Different protein to lipid ratios of 1:80, 1:90 and 1:100 were used for the assembly reaction, which were consecutively separated, purified and analyzed by size-exclusion chromatography (SEC) and dynamic light scattering (DLS). Size distributions were measured to determine homogeneity and confirm size dimensions. In this study, first evidence is presented on the formation of nanoscale particles with rhamnolipid biosurfactants and membrane scaffold proteins.

Novel insights into biosynthesis and uptake of rhamnolipids and their precursors

The human pathogenic bacterium Pseudomonas aeruginosa produces rhamnolipids, glycolipids with functions for bacterial motility, biofilm formation, and uptake of hydrophobic substrates. Rhamnolipids represent a chemically heterogeneous group of secondary metabolites composed of one or two rhamnose molecules linked to one or mostly two 3-hydroxyfatty acids of various chain lengths. The biosynthetic pathway involves rhamnosyltransferase I encoded by the rhlAB operon, which synthesizes 3-(3-hydroxyalkanoyloxy)alkanoic acids (HAAs) followed by their coupling to one rhamnose moiety. The resulting mono-rhamnolipids are converted to di-rhamnolipids in a third reaction catalyzed by the rhamnosyltransferase II RhlC. However, the mechanism behind the biosynthesis of rhamnolipids containing only a single fatty acid is still unknown. To understand the role of proteins involved in rhamnolipid biosynthesis the heterologous expression of rhl-genes in non-pathogenic Pseudomonas putida KT2440 strains was used in this study to circumvent the complex quorum sensing regulation in P. aeruginosa. Our results reveal that RhlA and RhlB are independently involved in rhamnolipid biosynthesis and not in the form of a RhlAB heterodimer complex as it has been previously postulated. Furthermore, we demonstrate that mono-rhamnolipids provided extracellularly as well as HAAs as their precursors are generally taken up into the cell and are subsequently converted to di-rhamnolipids by P. putida and the native host P. aeruginosa. Finally, our results throw light on the biosynthesis of rhamnolipids containing one fatty acid, which occurs by hydrolyzation of typical rhamnolipids containing two fatty acids, valuable for the production of designer rhamnolipids with desired physicochemical properties.

High-performance thin-layer chromatography (HPTLC) for the simultaneous quantification of the cyclic lipopeptides Surfactin, Iturin A and Fengycin in culture samples of Bacillus species

A high-performance thin-layer chromatography method has been established for the identification and simultaneous quantification of the cyclic lipopeptides Surfactin, Iturin A and Fengycin in Bacillus culture samples. B. subtilis DSM 10^T, B. amyloliquefaciens DSM 7^T and B. methylotrophicus DSM 23117 were used as model strains. Culture samples indicated that a sample pretreatment is necessary in order to run HPTLC analyses. A threefold extraction of the cell-free broth with the solvent chloroform/methanol (2:1, v/v) gave best results, when all three lipopeptides were included in the analysis. For the mobile phase, a two-step development was considered most suitable. The first development is conducted with chloroform/methanol/water (65:25:4, v/v/v) over a migration distance of 60mm and the second development using butanol/ethanol/0.1% acetic acid (1:4:1, v/v/v) over a migration distance of 60mm, as well. The method was validated according to Validation of Analytical Procedures: Methodology (FDA Guidance) with respect to the parameters linearity, limit of detection (LOD), limit of quantification (LOQ), precision, accuracy and recovery rate. A linear range with R²>0.99 was obtained for all samples from 30ng/zone up to 600ng/zone. The results indicated that quantification of Surfactin has to be performed after the first development (hR_F=44), while Fengycin is quantified after the second development (hR_F=36, hR_F range=20-40). For Iturin A, the results demonstrated that quantification is in favor after the first (hR_F=19) development, but also possible after the second (hR_F=59) development. LOD and LOQ for Surfactin and Iturin A after the first development, and Fengycin after the second development were determined to be 16ng/zone and 47ng/zone, 13ng/zone and 39ng/zone, and 27ng/zone and 82ng/zone, respectively. Results further revealed the highly accurate and precise character of the developed method with a good inter- and intraday reproducibility. For the precision and accuracy, expressed as % recovery and relative standard deviation, respectively, the determined values did not exceed ±15% as specified by the FDA Guidance. The recovery assay conducted for samples obtained from two strains with the solvent chloroform/methanol (2:1, v/v), which was determined to be most suitable if all three lipopeptides are of interest, gave recoveries of 96.5% and 99.6%, 68.6% and 71.6%, and 102.5% and 95.2% for Surfactin, Iturin A and Fengycin, respectively. Overall, a suitable and reliable method for the simultaneous quantification of the lipopeptides Surfactin, Iturin A and Fengycin in biological samples using HPTLC was successfully developed and validated.

Substitution of the native srfA promoter by constitutive Pveg in two B. subtilis strains and evaluation of the effect on Surfactin production

The genetic enhancement of Surfactin production increasingly gained attention in the last years, since relatively low product yields limit the industrial application of this biosurfactant. The natural quorum sensing regulation of the srfA operon (coding for the Surfactin synthetase) can reasonably be assumed to be the bottleneck of Surfactin synthesis. Therefore, the replacement of the naturally quorum sensing regulated, and herewith cell density dependent, promoter PsrfA against the Bacillus subtilis endogenous and constitutive promoter Pveg was hypothesized to generally enhance Surfactin yields. The markerless promoter replacement was conducted in the two B. subtilis Surfactin producer strains 3A38 and DSM 10(T). The promoter substitution led to an enhancement of Surfactin concentrations in the producer strain 3A38, initially producing only minor amounts of Surfactin (0.07g/L increased to 0.26g/L). In contrast, promoter exchange in B. subtilis DSM 10(T) (wild-type strain producing 0.62g/L Surfactin) did not achieve an enhancement of Surfactin concentrations (detrimental reduction to 0.04g/L). These findings implicate that Surfactin synthesis is differently regulated in minor and strong Surfactin producer strains. The hypothesized general enhancement of Surfactin yields after substitution of the native promoter was therefore not confirmed.

Integrated foam fractionation for heterologous rhamnolipid production with recombinant Pseudomonas putida in a bioreactor

Heterologeous production of rhamnolipids in Pseudomonas putida is characterized by advantages of a non-pathogenic host and avoidance of the native quorum sensing regulation in Pseudomonas aeruginosa. Yet, downstream processing is a major problem in rhamnolipid production and increases in complexity at low rhamnolipid titers and when using chemical foam control. This leaves the necessity of a simple concentrating and purification method. Foam fractionation is an elegant method for in situ product removal when producing microbial surfactants. However, up to now in situ foam fractionation is nearly exclusively reported for the production of surfactin with Bacillus subtilis. So far no cultivation integrated foam fractionation process for rhamnolipid production has been reported. This is probably due to excessive bacterial foam enrichment in that system. In this article a simple integrated foam fractionation process is reported for heterologous rhamnolipid production in a bioreactor with easily manageable bacterial foam enrichments. Rhamnolipids were highly concentrated in the foam during the cultivation process with enrichment factors up to 200. The described process was evaluated at different pH, media compositions and temperatures. Foam fractionation processes were characterized by calculating procedural parameter including rhamnolipid and bacterial enrichment, rhamnolipid recovery, Y_X/S, Y_P/X, and specific as well as volumetric productivities. Comparing foam fractionation parameters of the rhamnolipid process with the surfactin process a high effectiveness of the integrated foam fractionation for rhamnolipid production was demonstrated.

Teaching bioprocess engineering to undergraduates: Multidisciplinary hands-on training in a one-week practical course

Bioprocess engineering is a highly interdisciplinary field of study which is strongly benefited by practical courses where students can actively experience the interconnection between biology, engineering, and physical sciences. This work describes a lab course developed for 2nd year undergraduate students of bioprocess engineering and related disciplines, where students are challenged with a real-life bioprocess-engineering application, the production of recombinant protein in a fed-batch process. The lab course was designed to introduce students to the subject of operating and supervising an experiment in a bioreactor, along with the analysis of collected data and a final critical evaluation of the experiment. To provide visual feedback of the experimental outcome, the organism used during class was Escherichia coli which carried a plasmid to recombinantly produce enhanced green fluorescent protein (eGFP) upon induction. This can easily be visualized in both the bioreactor and samples by using ultraviolet light. The lab course is performed with bioreactors of the simplest design, and is therefore highly flexible, robust and easy to reproduce. As part of this work the implementation and framework, the results, the evaluation and assessment of student learning combined with opinion surveys are presented, which provides a basis for instructors intending to implement a similar lab course at their respective institution.

Rhamnolipids Production by a Pseudomonas eruginosa LBI Mutant: Solutions and Homologs Characterization

This paper evaluates the effect of additives (NaCl and ethanol) on the solution properties of rhamnolipids. The properties are the surface activity, aggregate formations and emulsifying activity as well as the synergistic effects of additives and pH variations on the physical properties of rhamnolipids. Additionally, analysis of fatty acids and rhamnolipid homologues produced using different carbon sources was performed by mass spectrometry. The results indicate that this biosurfactant maintain its properties in the presence of additives. NaCl decreases the size and number of aggregates formed in solutions without pH control, while ethanol to rhamnolipid solutions reduces critical micelle concentration and favors aggregation of monomers. The profiles of fatty acids produced by P. aeruginosa LBI 2A1 varied according to the carbon source used, however for rhamnolipids there was no difference.

Influence of ferric iron on gene expression and rhamnolipid synthesis during batch cultivation of Pseudomonas aeruginosa PAO1

Bioprocesses based on sustainable resources and rhamnolipids in particular have become increasingly attractive in recent years. These surface-active glycolipids with various chemical and biological properties have diverse biotechnological applications and are naturally produced by Pseudomonas aeruginosa. Their production, however, is tightly governed by a complex growth-dependent regulatory network, one of the major obstacles in the way to upscale production. P. aeruginosa PAO1 was grown in shake flask cultures using varying concentrations of ferric iron. Gene expression was assessed using quantitative PCR. A strong increase in relative expression of the genes for rhamnolipid synthesis, rhlA and rhlC, as well as the genes of the pqs quorum sensing regulon was observed under iron-limiting conditions. Iron repletion on the other hand caused a down-regulation of those genes. Furthermore, gene expression of different iron regulation-related factors, i.e. pvdS, fur and bqsS, was increased in response to iron limitation. Ensuing from these results, a batch cultivation using production medium without any addition of iron was conducted. Both biomass formation and specific growth rates were not impaired compared to normal cultivation conditions. Expression of rhlA, rhlC and pvdS, as well as the gene for the 3-oxo-C12-HSL synthetase, lasI, increased until late stationary growth phase. After this time point, their expression steadily decreased. Expression of the C4-HSL synthetase gene, rhlI, on the other hand, was found to be highly increased during the entire process.

Kinetic modeling of the time course of N-butyryl-homoserine lactone concentration during batch cultivations of Pseudomonas aeruginosa PAO1

Quorum sensing affects the regulation of more than 300 genes in Pseudomonas aeruginosa, influencing growth, biofilm formation, and the biosynthesis of several products. The quorum sensing regulation mechanisms are mostly described in a qualitative character. Particularly, in this study, the kinetics of N-butyryl-homoserine lactone (C4-HSL) and rhamnolipid formation in P. aeruginosa PAO1 were of interest. In this system, the expression of the rhamnolipid biosynthesis genes rhlAB is directly coupled to the C4-HSL concentration via the rhl system. Batch cultivations in a bioreactor with sunflower oil have been used for these investigations. 3-oxo-dodecanoyl-homoserine lactone (3o-C12-HSL) displayed a lipophilic character and accumulated in the hydrophobic phase. Degradation of C4-HSL has been found to occur in the aqueous supernatant of the culture by yet unknown extracellular mechanisms, and production was found to be proportional to biomass concentration rather than by autoinduction mechanisms. Rhamnolipid production rates, as determined experimentally, were shown to correlate linearly with the concentration of autoinducer C4-HSL. These findings were used to derive a simple model, wherein a putative, extracellular protein with C4-HSL degrading activity was assumed (putative C4-HSL acylase). The model is based on data for catalytic efficiency of HSL-acylases extracted from literature (k cat/K m), experimentally determined basal C4-HSL production rates (q C4 - HSL (basal)), and two fitted parameters which describe the formation of the putative acylase and is therefore comparatively simple.