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Journal: ACS synthetic biology


Sustainable and personally tailored materials production is an emerging challenge to society. Living organisms can produce and pattern an extraordinarily wide range of different molecules in a sustainable way. These natural systems offer an abundant source of inspiration for the development of new environmentally-friendly materials production techniques. In this paper, we describe the first steps towards the 3-dimensional printing of bacterial cultures for materials production and patterning. This methodology combines the capability of bacteria to form new materials with the reproducibility and tailored approach of 3D printing systems. For this purpose, a commercial 3D printer was modified for bacterial systems, and new alginate-based bio-ink chemistry was developed. Printing temperature, printhead speed, and bio-ink extrusion rate were all adapted and customized to maximize bacterial health and spatial resolution of printed structures. Our combination of 3D printing technology with biological systems enables a sustainable approach for the production of numerous new materials.

Concepts: DNA, Gene, Genetics, Bacteria, Biology, Organism, Printing, Inkjet printer


Tools to systematically reprogram cellular behavior are crucial to address pressing challenges in manufacturing, the environment, or healthcare. Recombinases can very efficiently encode Boolean and history-dependent logic in many species, yet current designs are performed on a case-by-case basis, limiting their scalability and requiring time-consuming optimization. Here we present an automated workflow for designing recombinase logic devices executing Boolean functions. Our theoretical framework uses a reduced library of computational modules distributed into different cellular subpopulations which are then composed in various manners to implement all desired logic functions at the multicellular level. Our design platform called CALIN (Composable Asynchronous Logic using Integrase Networks) is broadly accessible via a web server taking truth tables as inputs and providing corresponding DNA designs and sequences as outputs (available at: http:/

Concepts: Logic, Design, Design management, Boolean logic, Logical connective, Truth table, Boolean algebra, Boolean function


The volumetric heating values of today’s biofuels are too low to power energy-intensive aircraft, rockets, and missiles. Recently, pinene dimers were shown to have a volumetric heating value similar to that of the tactical fuel JP-10. To provide a sustainable source of pinene, we engineered Escherichia coli for pinene production. We combinatorially expressed three pinene synthases (PS) and three geranyl diphosphate synthases (GPPS), with the best combination achieving ∼28 mg/L of pinene. We speculated that pinene toxicity was limiting production; however, toxicity should not be limiting at current titers. Because GPPS is inhibited by geranyl diphosphate (GPP) and to increase flux through the pathway, we combinatorially constructed GPPS-PS protein fusions. The Abies grandis GPPS-PS fusion produced 32 mg/L of pinene, a 6-fold improvement over the highest titer previously reported in engineered E. coli. Finally, we investigated the pinene isomer ratio of our pinene-producing microbe and discovered that the isomer profile is determined not only by the identity of the PS used but also by the identity of the GPPS with which the PS is paired. We demonstrated that the GPP concentration available to PS for cyclization alters the pinene isomer ratio.

Concepts: Protein, Bacteria, Antibiotic resistance, Escherichia coli, Biotechnology, Enterobacteriaceae, Escherichia, Proteobacteria


Rose has been entwined with human culture and history. “Blue rose” in English signifies unattainable hope or impossible mission as it does not exist naturally and is not breedable regardless of centuries of efforts by gardeners. With the knowledge of genes and enzymes involved in flower pigmentation and modern genetic technologies, synthetic biologists have undertaken the challenge of producing blue rose by engineering the complicated vacuolar flavonoid pigmentation pathway and resulted in a mauve coloured rose. A completely different strategy presented in this study employs a dual expression plasmid containing bacterial idgS and sfp genes. The holo-IdgS, activated by Sfp from its apo-form, is a functional non-ribosomal peptide synthetase that converts L-glutamine into a blue pigment indigoidine. Expression of these genes upon petal injection with agro-infiltration solution generates blue-hued rose flowers. We envision that implementing this proof-of-concept with obligatory modifications may have tremendous impact in floriculture to achieve historic milestone in rose breeding.


The ability to regulate endogenous gene expression is critical in biological research. Existing technologies, such as RNA interference, zinc-finger regulators, transcription-activator-like effectors, and CRISPR-mediated regulation, though proved to be competent in significantly altering expression levels, do not provide a quantitative adjustment of regulation effect. As a solution to this problem, we place CRISPR-mediated interference under the control of blue light: while dCas9 protein is constitutively expressed, guide RNA transcription is regulated by YF1-FixJ-PFixK2, a blue light responding system. With a computer-controlled luminous device, the quantitative relationship between target gene expression and light intensity has been determined. As the light intensifies, the expression level of target gene gradually ascends. This remarkable property enables sensor-CRISPRi to accurately interrogate cellular activities.

Concepts: DNA, Gene, Genetics, Gene expression, Transcription, Molecular biology, RNA, RNA polymerase


Recently, synthetic biologists have developed the Synthetic Biology Open Language (SBOL), a data exchange standard for descriptions of genetic parts, devices, modules, and systems. The goals of this standard are to allow scientists to exchange designs of biological parts and systems, to facilitate the storage of genetic designs in repositories, and to facilitate the description of genetic designs in publications. In order to achieve these goals, the development of an infrastructure to store, retrieve, and exchange SBOL data is necessary. To address this problem, we have developed the SBOL Stack, a Resource Description Framework (RDF) database specifically designed for the storage, integration, and publication of SBOL data. This database allows users to define a library of synthetic parts and designs as a service, to share SBOL data with collaborators, and to store designs of biological systems locally. The database also allows external data sources to be integrated by mapping them to the SBOL data model. The SBOL Stack includes two Web interfaces: the SBOL Stack API and SynBioHub. While the former is designed for developers, the latter allows users to upload new SBOL biological designs, download SBOL documents, search by keyword, and visualize SBOL data. Since the SBOL Stack is based on semantic Web technology, the inherent distributed querying functionality of RDF databases can be used to allow different SBOL stack databases to be queried simultaneously, and therefore, data can be shared between different institutes, centers, or other users.

Concepts: DNA, Gene, Genetics, Biology, Semantic Web, Resource Description Framework, Synthetic biology, Registry of Standard Biological Parts


Engineered T cells are transforming broad fields in biomedicine, yet our ability to control cellular activity at specific anatomical sites remains limited. Here we engineer thermal gene switches to allow spatial and remote control of transcriptional activity using pulses of heat. These gene switches are constructed from the heat shock protein HSP70B' (HSPA6) promoter, show negligible basal transcriptional activity, and activate within an elevated temperature window of 40-45°C. Using engineered Jurkat T cells implanted in vivo, we use plasmonic photothermal heating to trigger gene expression at specific sites to levels greater than 200-fold. We show that delivery of heat as thermal pulse trains significantly increase cellular thermal tolerance compared to continuous heating curves with identical area-under-the-curve (AUC), enabling long-term control of gene expression in Jurkat T cells. This approach expands the toolkit of remotely controlled genetic devices for basic and translational applications in synthetic immunology.

Concepts: DNA, Gene, Genetics, Gene expression, Transcription, Organism, Heat, RNA polymerase


L-malate is an important platform chemical that has extensive applications in the food, feed, and wine industries. Here, we synergistically engineered the carbon metabolism and redox metabolism in the cytosol and mitochondria of a previously engineered A. oryzae to further improve the L-malate titer and decrease the byproduct succinate concentration. First, the accumulation of the intermediate pyruvate was eliminated by overexpressing a pyruvate carboxylase from Rhizopus oryzae in the cytosol and mitochondria of A. oryzae and consequently, the L-malate titer increased 7.5%. Then, malate synthesis via glyoxylate bypass in the mitochondria was enhanced and citrate synthase in the oxidative TCA cycle was downregulated by RNAi, enhancing the L-malate titer by 10.7%. Next, the exchange of byproducts (succinate and fumarate) between the cytosol and mitochondria was regulated by the expression of a dicarboxylate carrier Sfc1p from Saccharomyces cerevisiae in the mitochondria, which increased L-malate titer 3.5% and decreased succinate concentration 36.8%. Finally, an NADH oxidase from Lactococcus lactis was overexpressed to decrease the NADH/NAD+ ratio, and the engineered A. oryzae strain produced 117.2 g/L L-malate and 3.8 g/L succinate, with an L-malate yield of 0.9 g/g corn starch and a productivity of 1.17 g/L/h. Our results showed that synergistic engineering of the carbon and redox metabolisms in the cytosol and mitochondria of A. oryzae effectively increased the L-malate titer, while simultaneously decreasing the concentration of the byproduct succinate. The strategies used in our work may be useful for the metabolic engineering of fungi to produce other industrially important chemicals.


Transplanting metabolic reactions from one species into another has many uses as a research tool with applications ranging from optogenetics to crop production. Ferredoxin (Fd), the enzyme that most often supplies electrons to these reactions, is often overlooked when transplanting enzymes from one species to another because most cells already contain endogenous Fd. However, we have shown that the production of chromophores used in Phytochrome B (PhyB) optogenetics, is greatly enhanced in mammalian cells by expressing bacterial and plant Fds with ferredoxin-NADP+ reductases (FNR). We delineated the rate limiting factors and found that the main metabolic precursor, heme, was not the primary limiting factor for producing either the cyanobacterial or plant chromophores, phycocyanobilin or phytochromobilin, respectively. In fact, Fd is limiting, followed by Fd+FNR and finally heme. Using these findings, we optimized the PCB production system and for the first time, combined it with a tissue penetrating red/far-red sensing PhyB optogenetic gene switch in animal cells. We further characterized this system in several mammalian cell lines using red and far-red light. Importantly, we found that the light-switchable gene system remains active for several hours upon illumination, even with a short light pulse and requires very small amounts of light for maximal activation. Boosting chromophore production by matching metabolic pathways with specific ferredoxin systems will enable the unparalleled use of the many PhyB optogenetic tools and has broader implications for optimizing synthetic metabolic pathways.

Concepts: DNA, Gene, Cell, Bacteria, Metabolism, Adenosine triphosphate, Enzyme, Organism


Engineering the bacteria present in animal microbiomes promises to lead to breakthroughs in medicine and agriculture, but progress is hampered by a dearth of tools for genetically modifying the diverse species that comprise these communities. Here we present a toolkit of genetic parts for the modular construction of broad-host-range plasmids built around the RSF1010 replicon. Golden Gate assembly of parts in this toolkit can be used to rapidly test various antibiotic resistance markers, promoters, fluorescent reporters and other coding sequences in newly isolated bacteria. We demonstrate the utility of this toolkit in multiple species of Proteobacteria that are native to the gut microbiomes of honey bees ( Apis mellifera) and bumble bees ( Bombus sp.). Expressing fluorescent proteins in Snodgrassella alvi, Gilliamella apicola, Bartonella apis, and Serratia strains enables us to visualize how these bacteria colonize the bee gut. We also demonstrate CRISPRi repression in B. apis and use Cas9-facilitated knockout of an S. alvi adhesion gene to show that it is important for colonization of the gut. Beyond characterizing how the gut microbiome influences the health of these prominent pollinators, this bee microbiome toolkit (BTK) will be useful for engineering bacteria found in other natural microbial communities.

Concepts: DNA, Gene, Bacteria, Evolution, Honey bee, Bee, Bumblebee, Apidae