Optimization of Phycocyanobilin Synthesis in E. coli BL21: Biotechnological Insights and Challenges for Scalable Production.

Phycocyanobilin (PCB) is a small chromophore found in certain phycobiliproteins, such as phycocyanins (PCs) and allophycocyanins (APCs). PCB, along with other phycobilins (PBs) and intermediates such as biliverdin (BV) or phycoerythrobilin (PEB), is attracting increasing biotechnological interest due to its fluorescent and medicinal properties that allow potential applications in biomedicine and the food industry. This study aims to optimize PCB synthesis in Escherichia coli BL21 (DE3) and scale the process to a pre-industrial level. Parameters such as optimal temperature, inducer concentration, initial OD600, and stirring speed were analyzed in shake flask cultures to maximize PCB production. The best results were obtained at a temperature of 28 °C, an IPTG concentration of 0.1 mM, an initial OD600 of 0.5, and an orbital shaking speed of 260 rpm. Furthermore, the optimized protocol was scaled up into a 2 L bioreactor batch, achieving a maximum PCB concentration of 3.8 mg/L. Analysis of the results revealed that biosynthesis of exogenous PBs in Escherichia coli BL21 (DE3) is highly dependent on the metabolic burden of the host. Several scenarios, such as too rapid growth, high inducer concentration, or mechanical stress, can advance entry into the stationary phase. That progressively halts pigment synthesis, leading, in some cases, to its excretion into the growth media and ultimately triggering rapid degradation by the host. These conclusions provide a promising protocol for scalable PCB production and highlight the main biotechnological challenges to increase the yields of the process.

Engineering bacteria to form a biofilm and induce clumping in Caenorhabditis elegans.

Bacteria are needed for a vast range of biotechnological processes, which they carry out either as pure cultures or in association with other bacteria and/or fungi. The potential of bacteria as biofactories is hampered, though, by their limited mobility in solid or semisolid media such as agricultural or domestic waste. This work represents an attempt toward overcoming this limitation by associating bacterial biotechnological properties with the transport ability of the nematode Caenorhabditis elegans. We report here biofilm formation on C. elegans by engineered Escherichia coli expressing a Xhenorhabdus nematophila adhesion operon and induction of nematode social feeding behavior (clumping) through an E. coli-mediated iRNA blocking on the expression of FLP-21, a neuropeptide involved in worm solitary behavior.