Biotechnol. Appl. Biochem. (2010) 55, 00–00 (Printed in Great Britain) doi:10.1042/BA20090277 1 Production of rhamnolipid biosurfactants by Pseudomonas aeruginosa DS10-129 in a microfluidic bioreactor Q1 Pattanathu K. S. M. Rahman 1 , Godfrey Pasirayi, Vincent Auger and Zulfiqur Ali Chemical and Bioprocess Engineering Group, School of Science and Engineering, Teesside University, Middlesbrough-TS1 3BA, Tees Valley, U.K. A low-cost μBR (microbioreactor) made from f PTFE [poly(tetrafluoroethylene)] was used to cultivate a model organism, Pseudomonas aeruginosa DS10-129. The progress of bioprocessing was monitored by comparing the growth of the organism in a μBR, a conventional bench scale bioreactor and a shake flask. Under the μBR conditions, the organism Q3 produced 23 mg/ml of pyocyanin that had antimicrobial effects against Bacillus subtilis, Staphylococcus aureus, Staphylococcus epidermidis, Pseudomonas teessidea and Pseudomonas clemancea. Furthermore, it produced a total of 106 μg/ml of effective biosurfactants consisting of dirhamnolipids (RL2) and monorhamnolipids (RL1). The biosurfactants reduced the surface tension of distilled water from 72 to 27.9 mN/m and emulsified kerosene by 71.30%. The pyocyanin and rhamnolipids were produced during the exponential and stationary phases of growth respectively. The results of the μBR were comparable to those obtained using the conventional scale methods. Introduction The development of microfluidic systems over the past Q4 decade has been remarkable worldwide. Microfluidic technology offers certain advantages such as utilization of small sample size, the integration of sample handling and measurement function on one chip, ability to improve analytical performance, lower production and operational costs, and ease of use. Reports have shown that the global market for microfluifics technology is steadily rising to several billions of dollars as companies are actively pursuing the commercialization of their systems [1]. μBRs (microbioreactors) represent a type of complex microfludic systems that are a scaled-down version mimicking the conventional scale bioreactor systems. They are low-cost modules providing data-rich solutions useful to optimize conventional scale operations and offering highly parallel analytical platforms in high-throughput bioprocessing. The attractive features of μBRs have resulted in their use in a number of fields such as drug discovery, tissue engineering, strain development, cell-based screening and bioprocess optimization. Their low volume has the advantage of supporting small bacterial populations, which allows long- time monitoring of cell behaviour. Furthermore, μBRs have the added potential of lowering the cost of conducting research and increasing the process development rate. It is clear from these developments that μBRs are promising tools that can potentially overcome the bottlenecks (non-integration of systems, labour-intensive, high operational costs and prolonged time for cell cultivation) currently encountered in macroscale operations. In the literature, many researchers have reported various designs to manufacture μBRs. For example, Kim et al. [2] reported a silicon microfermentor chip that used electrodes to measure cell density, pH and dissolved oxygen. Zanzotto et al. [3] and Kostov et al. [4] developed and demonstrated a low-cost microfluidic bioreactor for high- throughput bioprocessing using Escherichia coli as the model organism. The results showed that E. coli cultivation in the μBR was identical with the results obtained in conventional systems [SF (shake flask) and bench bioreactor]. In other studies, Szita et al. [5] demonstrated a 150 μl membrane aerated well-mixed polymer-based μBR system integrated with attenuance, pH and dissolved oxygen sensors with real- Q5 time measurements and concluded that a microchemostat was an effective tool for bioprocessing. Walther et al. [6] developed a 3 ml continuous bioreactor with integrated microelectronic sensors for biomass, pH and temperature to investigate the physiological and morphological properties of yeast cells in microgravity environments in a space laboratory. Steinhaus et al. [7] developed a portable aerobic microfluidic bioreactor with microchannels of different widths to study the optimum growth conditions for the Key words: antimicrobial activity, biosurfactant, high-throughput bioprocessing, microbioreactor (μBR), microfluidic bioreactor, rhamnolipid. Abbreviations used: ANTBM1, antibiotic medium number 1; BSBR, bench scale bioreactor; cfu, colony-forming units; CMC, critical micelle concentration; CTAB, cetyltrimethylammonium bromide; FTIR, Fourier-transform infrared; NB, nutrient broth; GSNB, glycerol-supplemented NB; MBA, Methylene Blue agar; μBR, microbioreactor; NA, nutrient agar; PTFE, poly(tetrafluoroethylene); SF, shake flask. 1 To whom correspondence should be addressed (email p.rahman@tees.ac.uk). C  2010 Portland Press Ltd