Parallel use of shake flask and microtiter plate online measuring devices (RAMOS and BioLector) reduces the number of experiments in laboratory-scale stirred tank bioreactors

Background Conventional experiments in small scale are often performed in a Black Box fashion, analyzing only the product concentration in the final sample. Online monitoring of relevant process characteristics and parameters such as substrate limitation, product inhibition and oxygen supply is lacking. Therefore, fully equipped laboratory-scale stirred tank bioreactors are hitherto required for detailed studies of new microbial systems. However, they are too spacious, laborious and expensive to be operated in larger number in parallel. Thus, the aim of this study is to present a new experimental approach to obtain dense quantitative process information by parallel use of two small-scale culture systems with online monitoring capabilities: Respiration Activity MOnitoring System (RAMOS) and the BioLector device. Results The same mastermix (medium plus microorganisms) was distributed to the different small-scale culture systems: 1) RAMOS device; 2) 48-well microtiter plate for BioLector device; and 3) separate shake flasks or microtiter plates for offline sampling. By adjusting the same maximum oxygen transfer capacity (OTRmax), the results from the RAMOS and BioLector online monitoring systems supplemented each other very well for all studied microbial systems (E. coli, G. oxydans, K. lactis) and culture conditions (oxygen limitation, diauxic growth, auto-induction, buffer effects). Conclusions The parallel use of RAMOS and BioLector devices is a suitable and fast approach to gain comprehensive quantitative data about growth and production behavior of the evaluated microorganisms. These acquired data largely reduce the necessary number of experiments in laboratory-scale stirred tank bioreactors for basic process development. Thus, much more quantitative information is obtained in parallel in shorter time.Cluster of Excellence “Tailor-Made Fuels from Biomass”, which is funded by the Excellence Initiative by the German federal and state governments to promote science and research at German universities

Sleep-amount differentially affects fear-processing neural circuitry in pediatric anxiety: A preliminary fMRI investigation

Insufficient sleep, as well as the incidence of anxiety disorders, both peak during adolescence. While both conditions present perturbations in fear-processing-related neurocircuitry, it is unknown whether these neurofunctional alterations directly link anxiety and compromised sleep in adolescents. Fourteen anxious adolescents (AAs) and 19 healthy adolescents (HAs) were compared on a measure of sleep amount and neural responses to negatively valenced faces during fMRI. Group differences in neural response to negative faces emerged in the dorsal anterior cingulate cortex (dACC) and the hippocampus. In both regions, correlation of sleep amount with BOLD activation was positive in AAs, but negative in HAs. Follow-up psychophysiological interaction (PPI) analyses indicated positive connectivity between dACC and dorsomedial prefrontal cortex, and between hippocampus and insula. This connectivity was correlated negatively with sleep amount in AAs, but positively in HAs. In conclusion, the presence of clinical anxiety modulated the effects of sleep-amount on neural reactivity to negative faces differently among this group of adolescents, which may contribute to different clinical significance and outcomes of sleep disturbances in healthy adolescents and patients with anxiety disorders

Mathematische Modellierung einer drei Spezies Mischkultur im Chemostat

Staphylococcus aureus, Burkholderia cepacia und Pseudomonas aeruginosa sind drei der bakteriellen Spezies, welche die Lunge von Patienten mit Cystischer Fibrose infizieren können. Für eine effiziente Bekämpfung sind umfangreiche Kenntnisse über Wachstumseigenschaften und Wachstumsbedingungen von essentieller Bedeutung. Zu diesem Zweck soll im Rahmen eines Forschungsprojektes diese Mischkultur reproduzierbar generiert werden. Das entstehende Modellsystem soll zu einem allgemein besseren Verständnis beitragen und Experimente (z. B. Versuche zur Wirksamkeit von Antibiotika) unter kontrollierten Bedingungen ermöglichen. Um dieses Ziel zu erreichen, wurden für die vorliegenden Diplomarbeit die drei Spezies S. aureus, B. cepacia und P. aeruginosa in definiertem Vollmedium zunächst einzeln kultiviert. Es konnten dadurch die Stoffwechsel aller drei Spezies charakterisiert und mittels mathematischer Modelle beschrieben werden. Zu diesem Zweck wurden Mischsubstratkinetiken und einfache Monod-Kinetiken angewendet. Durchgeführte Mischkultur-Experimente im Chemostat (D = 0,2 h-1), zeigten das Überleben aller drei Spezies für mindestens 235 h. Um zum Verständnis dieses Ergebnisses beizutragen, wurden, basierend auf Reinkulturmodellen, Mischkulturmodelle aufgestellt. Eines dieser Modelle war in der Lage die Koexistenz der beiden Spezies P. aeruginosa und B. cepacia zu beschreiben. Die Spezies S. aureus wurde in der durchgeführten Modellsimulation ausgewaschen und war damit nicht in der Lage das experimentelle Ergebnis vollständig wiederzugeben. In weiterführenden Arbeiten sollte die Parameterbestimmung für alle Reinkulturmodelle verbessert werden. Für die Modellierung der Mischkulturen, sollten weitere mögliche Interaktionen zwischen den Spezies berücksichtigt werden, die aufgrund des bislang noch vorhandenen Widerspruchs zwischen Modellsimulation und experimentellen Ergebnis anzunehmen sind

A Medically Relevant Three-Species Mixed Culture in a Chemostat : Mathematical Modelling and Experiments to Study Interaction Effects

Pseudomonas aeruginosa, Burkholderia cepacia and Staphylococcus aureus are opportunistic infectants which occur as mixed cultures in the lungs of cystic fibrosis (CF) patients. Knowledge on possible interactions and growth characteristics of the microbial community in the lung obviously cannot be obtained in situ. It would be very desirable to be able to predict the mixed culture’s reaction, e.g. on antibiotic treatment, for optimal therapy of patients. We set up a laboratory chemostat to quantitatively study the three species as a reproducible mixed culture under completely defined and controllable conditions [1]. Our focus was to find possible interactions by combination of experiments and mathematical modelling. Choice of a chemically defined culture medium primarily consisting of glucose and amino acids allowed for quantitative analysis of metabolic substrates and products. Absolute and species-specific cell numbers were determined by a quantitative T-RFLP analysis method [1]. Experiments showed an apparent coexistence of at least two of the species for more than 32 volume exchanges. This result was not predictable with a model assuming pure substrate competition [2]. Therefore, additional model assumptions were implemented and tested by comparison to experimental results. We present two selected interactions that were analysed in detail. One effect was that of a metabolic interaction, i.e. in this case the metabolic product of one species could serve as substrate for the two other species. The effect was shown mathematically to be a premise for coexistence, but not in the case for our species [2]. Another effect was that of amino acids as an additional substrate to glucose. The standard assumption for chemostat cultivations is that there is only one limiting substrate. It is known, that medium components can serve as co-substrate, mixed substrate or second carbon source [3]. This is rarely taken into account, when investigating pure or even mixed chemostat cultures. With a glucose-free variant of the chemically defined medium different hypotheses on the specific function of the amino acids were tested for each of the three species. Additionally, selected scenarios of the mixed culture outcome for variation of the implemented assumptions will be presented. We show, that even our laboratory model system is too complex to be described by the reduced assumptions of single-substrate competition, but that specific single species properties need to be considered to describe the mixed culture behaviour. The combination of mathematical modelling and quantitative experimental studies has to our knowledge not been presented before for a more than two species microbial community in such detail and quantitative quality. Further investigations will follow the same approach in studying the effects of antibiotic pulses on the dynamics of the mixed culture. [1] Schmidt, J.K. et al.: (2006) Biotech Bioeng (published online) [2] Heßeler, J. et al.: (2006) J Math Biol 53: 556-584 [3] Kovarova-Kovar K. et al.: (1998) Microbiol Mol Bio Rev: 646-66

Analysis of a Medically Relevant Microbial Community in a Bioreactor

Pseudomonas aeruginosa, Burkholderia cepacia and Staphylococcus aureus are opportunistic infectants, which occur as mixed cultures in the lungs of cystic fibrosis (CF) patients. Knowledge on possible interactions and growth characteristics of the microbial community in the lung obviously cannot be obtained in situ. It would be very desirable to be able to predict the mixed culture’s reaction, e.g. on antibiotic treatment, for optimal therapy of patients. We established a mixed culture in a chemostat bioreactor and use it as a model system related to the microbial community in CF lungs. Our experimental setup ensures defined and controllable conditions for the mixed culture and highly reproducible results. With comprehensive quantitative analytical methods we study bacterial growth characteristics and metabolic activity. In combination with mathematical modelling we focus on identifying microbial interactions and analyze the dynamics of the system, e.g. by disturbing the quasi steady state in chemostat experiments. In previous studies an apparent coexistence of at least two of the species was shown for more than 33 volume exchanges [1]. Also with complex models that e.g. include amino acids alternatively as a) co-substrate, b) mixed substrate or c) second carbon source, the experimental results of the three species culture could not be described in silico with adequate accuracy. This indicates that additional single species properties or interactions between the different species need to be included in corresponding models. From antibiotic pulse experiments we hope to gain further insight about the validity of existing models and learn more about possible other interactions. For measuring absolute and species specific cell numbers in mixed culture samples, a quantitative T-RFLP method was established and optimized [1]. Here, we show the applicability of our method as a valid quantification tool for cell numbers of the three species in single and mixed culture after treatment with ceftazidim, an antibiotic used in therapy of CF-patients. T-RFLP derived cell numbers are compared to plate counts and viability staining as reference methods. Additionally, we will present results of antibiotic pulse experiments and simulation studies of single and mixed cultures. The experimental part was realized in stirred tank reactors in a parallel small-scale system with off-gas analyser and a digital process control system (VL = 200 mL, fedbatch-pro®, GA4 and EasyAccess, dasgip, Germany). For modelling and simulation Matlab 7.1 (The MathWorks, Inc.) was used. Quantitative analysis of amino acids and ceftazidim was done by HPLC methods (anion exchange chromatography, DX600, Dionex and reversed phase chromatography, Agilent 1200, Agilent). Glucose was determined with an automated enzyme detector (YSI 7100 MBS, Kreienbaum wiss. Meßsysteme). [1] Schmidt, J.K. et al.: (2007) BiotechBioeng 96(4):738-75