Pamela J. Weathers

Microalgal bioreactors: challenges and opportunities.

Cultivating and harvesting of products from microalgae has led to increasing commercial interest in their use for producing valuable substances for food, feed, cosmetics, pharmaceuticals, and biodiesel, as well as for mitigation of pollution and rising CO2 in the environment. This review outlines different bioreactors and their current status, and points out their advantages and disadvantages. Compared with open‐air systems, there are distinct advantages to using closed systems, but technical challenges still remain. In view of potential applications, development of a more controllable, economical, and efficient closed culturing system is needed. Further developments still depend on continued research in the design of photobioreactors and break‐throughs in microalgal culturing technologies.

Production of Mouse Interleukin-12 Is Greater in Tobacco Hairy Roots Grown in a Mist Reactor Than in an Airlift Reactor

We compared the growth and productivity of a tobacco line of hairy roots that produces murine interleukin 12 (mIL‐12) grown in three different culture systems: shake flasks, an airlift reactor, and a scalable mist reactor. Of the total mIL‐12 produced by cultures grown in shake flasks (∼434.8 µg L−1), almost 21% was recovered from the medium. In contrast to roots harvested from shake flasks and the mist reactor, roots were not uniformly distributed in the airlift reactor. Roots formed a dense ring around the wall of the reactor and surrounding the central rising column of fine aeration bubbles. Root quality was also better in both the shake flasks and mist reactor than in the airlift reactor. There were more pockets of dark roots in the airlift reactor suggesting some of the roots were nutrient starved. Although the best root growth (7 g DW L−1) was in the shake flasks, both reactors produced about the same, but less dry mass, nearly 5 g DW L−1. Total mIL‐12 concentration was highest in the mist reactor at 5.3 µg g−1 FW, but productivity, 31 µg g−1 FW day−1 was highest in shake flasks. Roots grown in the mist reactor produced about 49.5% more mIL‐12 than roots grown in the airlift reactor. Protease activity in the media increased steadily during culture of the roots in all three systems. The comparisons of protease activity, protein and mIL‐12 levels done in the shake flask system suggest that the increase in proteases associated with progression into stationary phase is most detrimental to mIL‐12 concentration. This is the first description of the design and operation of a scalable version of a mist bioreactor that uses a plastic bag. This also the first report of reasonable production levels of functional mIL‐12, or any protein, produced by hairy roots grown in a mist reactor. Results will prove useful for further optimization and scale‐up studies of plant‐produced therapeutic proteins. Biotechnol. Bioeng. 2009;102: 1074–1086.

Platforms for Plant-Based Protein Production

Plant molecular farming depends on a diversity of plant systems for production of useful recombinant proteins. These proteins include protein biopolymers, industrial proteins and enzymes, and therapeutic proteins. Plant production systems include microalgae, cells, hairy roots, moss, and whole plants with both stable and transient expression. Production processes involve a narrowing diversity of bioreactors for cell, hairy root, microalgae, and moss cultivation. For whole plants, both field and automated greenhouse cultivation methods are used with J. Xu Arkansas Biosciences Institute, Arkansas State University, Jonesboro, AR, USA M. Towler · P. J. Weathers (*) Biology and Biotechnology Department, Worcester Polytechnic Institute, Worcester, MA, USA e-mail: weathers@wpi.edu # Springer International Publishing AG, part of Springer Nature 2018 A. Pavlov, T. Bley (eds.), Bioprocessing of Plant In Vitro Systems, Reference Series in Phytochemistry, https://doi.org/10.1007/978-3-319-54600-1_14 509 products expressed and produced either in leaves or seeds. Many successful expression systems now exist for a variety of different products with a list of increasingly successful commercialized products. This chapter provides an overview and examples of the current state of plant-based production systems for different types of recombinant proteins.