Engineering microbes to synthesize molecules of societal value has historically been a time consuming and artisanal process, with the synthesis of each new non-native molecule typically warranting its own separate publication. Because most microbial strain engineering efforts leverage a finite number of common metabolic engineering design tactics, we reasoned that automating these design steps would help create a pipeline that can quickly, cheaply, and reliably generate so-called microbial factories. In this work we describe the design and implementation of a computational system, an Automated Scientist we call Lila, which handles all metabolic engineering design and optimization through the design-build-test-learn (DBTL) paradigm. Lila generates metabolic routes, identifies relevant genetic elements for perturbation, and specifies the design and re-design of microbial strains in a matter of seconds to minutes. Strains specified by Lila are then built and subsequently phenotyped as part of a largely automated in-house pipeline. Humans remain in-the-loop to curate choices made by the system, helping for example to refine the metabolic model or suggest custom protein modifications. Lila attempted to build strains that could produce 454 biochemically diverse molecules with precursors located broadly throughout the metabolism of two microbial hosts, Saccharomyces cerevisiae and Escherichia coli . Notably, we observed the highest published titers for the molecule naringenin, the metabolic precursor to flavonoids. In total we created hundreds of thousands of microbial strains capable of overproducing 242 molecules, of which 180 are not native to S. cerevisiae or E. coli .

For commercial protein therapeutics, Chinese hamster ovary (CHO) cells have an established history of safety, proven capability to express a wide range of therapeutic proteins and high volumetric productivities. Expanding global markets for therapeutic proteins and increasing concerns for broadened access of these medicines has catalyzed consideration of alternative approaches to this platform. Reaching these objectives likely will require an order of magnitude increase in volumetric productivity and a corresponding reduction in the costs of manufacture. For CHO-based manufacturing, achieving this combination of targeted improvements presents challenges. Based on a holistic analysis, the choice of host cells was identified as the single most influential factor for both increasing productivity and decreasing costs. Here we evaluated eight wild-type eukaryotic micro-organisms with prior histories of recombinant protein expression. The evaluation focused on assessing the potential of each host, and their corresponding phyla, with respect to key attributes relevant for manufacturing, namely (a) growth rates in industry-relevant media, (b) adaptability to modern techniques for genome editing, and (c) initial characterization of product quality. These characterizations showed that multiple organisms may be suitable for production with appropriate engineering and development and highlighted that yeast in general present advantages for rapid genome engineering and development cycles.

Isoprenoids (terpenes/terpenoids) have many useful industrial applications, but are often not produced at industrially viable level in their natural sources. Synthetic biology approaches have been used extensively to reconstruct metabolic pathways in tractable microbial hosts such as yeast and re-engineer pathways and networks to increase yields. Here we review recent advances in this field, focusing on central carbon metabolism engineering to increase precursor supply, redirecting carbon flux for production of C10, C15, or C20 isoprenoids, and chemical decoration of high value diterpenoids (C20). We also overview other novel synthetic biology strategies that have potential utility in yeast isoprenoid pathway engineering. Finally, we address the question of what is required in the future to move the field forwards.

Isoprenoids (terpenes/terpenoids) have many useful industrial applications, but are often not produced at industrially viable level in their natural sources. Synthetic biology approaches have been used extensively to reconstruct metabolic pathways in tractable microbial hosts such as yeast and re-engineer pathways and networks to increase yields. Here we review recent advances in this field, focusing on central carbon metabolism engineering to increase precursor supply, re-directing carbon flux for production of C10, C15, or C20 isoprenoids, and chemical decoration of high value diterpenoids (C20). We also overview other novel synthetic biology strategies that have potential utility in yeast isoprenoid pathway engineering. Finally, we address the question of what is required in the future to move the field forwards.

The development of a cost-effective process for the production of artemisinin, the precursor of all artemisinin-derived drugs, the first-line treatment for malaria, has been a long-pursued endeavor. The breakthrough achievement of coaxing genetically engineered yeast to express Artemisia annua genes for the commercial production of artemisinic acid, an advanced intermediate in the synthesis of artemisinin, has yet to fully realize an affordable malaria treatment for the poor because of the lack of a cost-effective chemical conversion into artemisinin. We describe herein a commercially feasible and pragmatic synthesis of artemisinin from amorpha-4,11-diene, an early-stage intermediate produced in 2-fold higher molar yield than engineered yeast cells can process into artemisinic acid. The key to this novel approach is an exceedingly effective functionalization of the isopropenyl group of amorphadiene via endo-epoxyamorphadiene to give dihydroartemisinic acid, which upon esterification followed by oxidation and cyclicization furnishes pure artemisinin in approximately 60% yield.

selection of individuals from the biotech ecosystem give their views on the challenges facing the sector over the coming years.

Nat. Biotechnol. 34, 276–283 (2016); published online 10 March 2016; corrected after print 31 March 2016 In the version of this article initially published, Stanley Crooke's name was misspelled as “Crook” in the author list. The error has been corrected in the HTML and PDF versions of the article.

Industrial BiotechnologyVol. 11, No. 4 Roundtable DiscussionsSynthetic Biology-Based Microbial Conversion in Industrial ProcessesModerator: Kevin Jarrell, Participants: Kristala L.J. Prather, Joel Cherry, Emmanuel Petiot, and Todd PetersonModerator: Kevin JarrellCEO, Modular Genetics, Woburn, MASearch for more papers by this author, Participants: Kristala L.J. PratherAssociate Professor, Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, MASearch for more papers by this author, Joel CherryPresident, Research & Development, Amyris, Emeryville, CASearch for more papers by this author, Emmanuel PetiotCEO, Deinove, Grabels, FranceSearch for more papers by this author, and Todd PetersonChief Technology Officer, Synthetic Genomics, La Jolla, CASearch for more papers by this authorPublished Online:7 Aug 2015https://doi.org/10.1089/ind.2015.29004.kxjAboutSectionsView articleView Full TextPDF/EPUB Permissions & CitationsPermissionsDownload CitationsTrack CitationsAdd to favorites Back To Publication ShareShare onFacebookTwitterLinked InRedditEmail View articleFiguresReferencesRelatedDetails Volume 11Issue 4Aug 2015 InformationCopyright 2015, Mary Ann Liebert, Inc.To cite this article:Moderator:, Kevin Jarrell, Participants:, Kristala L.J. Prather, Joel Cherry, Emmanuel Petiot, and Todd Peterson.Synthetic Biology-Based Microbial Conversion in Industrial Processes.Industrial Biotechnology.Aug 2015.188-193.http://doi.org/10.1089/ind.2015.29004.kxjPublished in Volume: 11 Issue 4: August 7, 2015PDF download

Endoglucanases are important enzymes for biomass conversion and other industrial processes. Determining the specificity of endoglucanases from various glycoside hydrolase families is of interest for bioinformatic functional prediction and substrate-tailored enzyme development. To do so, we characterized approximately 30 endoglucanases from six glycoside hydrolase families. For p-nitrophenyl cellobioside and lactoside, only family 7 enzymes showed significant activity. For xyloglucan, both family 7 and 12 enzymes showed significant activity. For xylan and arabinoxylan, only family 7 enzymes showed significant activity. For mannan and galactomannan, both family 5 and 9 enzymes showed significant activity. The difference in specificity was preliminarily attributed mainly to the structural difference of the enzymes' active sites. For family 7 endoglucanases, difference in thermal stability might affect their performance in hydrolyzing various (hemi)cellulose substrates. Phylogenetic analysis on the subfamily distribution of family 5 endoglucanases (in relation with mannanases) suggested that their mannanase side-activity might be the remnant of an ancestral multi-function enzyme. Similar analysis was also made with the xyloglucanase or arabionxylans side-activity of family 12 and 7 endoglucanases. The apparent dependence of the specificity on family (primary/tertiary structure) might assist us in better understanding the structure-function relationship of the enzymes, and developing more versatile biocatalysts for the utilization of biomass.

Currently, the relatively high cost of enzymes such as glycoside hydrolases that catalyze cellulose hydrolysis represents a barrier to commercialization of a biorefinery capable of producing renewable transportable fuels such as ethanol from abundant lignocellulosic biomass. Among the many families of glycoside hydrolases that catalyze cellulose and hemicellulose hydrolysis, few are more enigmatic than family 61 (GH61), originally classified based on measurement of very weak endo-1,4-beta-d-glucanase activity in one family member. Here we show that certain GH61 proteins lack measurable hydrolytic activity by themselves but in the presence of various divalent metal ions can significantly reduce the total protein loading required to hydrolyze lignocellulosic biomass. We also solved the structure of one highly active GH61 protein and find that it is devoid of conserved, closely juxtaposed acidic side chains that could serve as general proton donor and nucleophile/base in a canonical hydrolytic reaction, and we conclude that the GH61 proteins are unlikely to be glycoside hydrolases. Structure-based mutagenesis shows the importance of several conserved residues for GH61 function. By incorporating the gene for one GH61 protein into a commercial Trichoderma reesei strain producing high levels of cellulolytic enzymes, we are able to reduce by 2-fold the total protein loading (and hence the cost) required to hydrolyze lignocellulosic biomass.

Directed evolution coupled with a high-throughput robotic screen was employed to broaden the industrial use of the maltogenic alpha-amylase Novamyl from Bacillus sp. TS-25. Wild-type Novamyl is currently used in the baking industry as an anti-staling agent in breads baked at neutral or near neutral pH. However, the enzyme is rapidly inactivated during the baking process of bread made with low pH recipes and Novamyl thus has very limited beneficial effect for this particular application. In an effort to improve the performance of Novamyl for low pH bread applications such as sourdough and rye, two error-prone PCR libraries were generated, expressed in Bacillus subtilis and screened for variants with improved thermal stability and activity under low pH conditions. Variants exhibiting improved performance were iteratively recombined using DNA shuffling to create two generations of libraries. Relative to wild-type Novamyl, a number of the resulting variants exhibited more than 10 degrees C increase in thermal stability at pH 4.5, one of which demonstrated substantial anti-staling properties in low pH breads.

The commercial cellulase product Celluclast 1.5, derived from Trichoderma reesei (Novozymes A/S, Bagsvaerd, Denmark), is widely employed for hydrolysis of lignocellulosic biomass feedstocks. This enzyme preparation contains a broad spectrum of cellulolytic enzyme activities, most notably cellobiohydrolases (CBHs) and endo-1,4-beta-glucanases (EGs). Since the original T. reesei strain was isolated from decaying canvas, the T. reesei CBH and EG activities might be present in suboptimal ratios for hydrolysis of pretreated lignocellulosic substrates. We employed statistically designed combinations of the four main activities of Celluclast 1.5, CBHI, CBHII, EGI, and EGII, to identify the optimal glucose-releasing combination of these four enzymes to degrade barley straw substrates subjected to three different pretreatments. The data signified that EGII activity is not required for efficient lignocellulose hydrolysis when addition of this activity occurs at the expense of the remaining three activities. The optimal ratios of the remaining three enzymes were similar for the two pretreated barley samples that had been subjeced to different hot water pretreatments, but the relative levels of EGI and CBHII activities required in the enzyme mixture for optimal hydrolysis of the acid-impregnated, steam-exploded barley straw substrate were somewhat different from those required for the other two substrates. The optimal ratios of the cellulolytic activities in all cases differed from that of the cellulases secreted by T. reesei. Hence, the data indicate the feasibility of designing minimal enzyme mixtures for pretreated lignocellulosic biomass by careful combination of monocomponent enzymes. This strategy can promote both a more efficient enzymatic hydrolysis of (ligno)cellulose and a more rational utilization of enzymes.