Tag Archives: synbio

Behind the paper: Four novel anti-CRISPR proteins found using synthetic biology

Last week our article on new anti-CRISPR proteins was published in Cell Host & Microbe. Anti-CRISPRs are small proteins that inhibit the activity of CRISPR-Cas. These days a lot of research is focused on finding more active CRISPR-Cas systems. So why does anyone want to reduce CRISPR-Cas activity?

A big challenge with CRISPR-Cas is that it cleaves DNA where it is not supposed to, known as the “off-target effect”. This means CRISPR-Cas can introduce mutations that are unwanted. Unwanted mutations are just one of the many concerns about the recently edited “CRISPR babies”, as they could pose potential and unknown dangers to human health. 

A solution to prevent off-target effects is to temporarily turn CRISPR-Cas activity off. This can be done using proteins that inhibit CRISPR-Cas activity. Some proteins mimic the DNA segment CRISPR-Cas is supposed to cut, while others prevent Cas9 from changing conformation. Until now, only a dozen anti-CRISPR proteins were known and are specific for their CRISPR-Cas type (see the figure below). So, it would be very useful to find more proteins that can inhibit CRISPR-Cas.

On the bottom the latest classification of CRISPR-Cas systems modified from Makarova and on the top the number of anti-CRISPR families found today as tracked by the anti-CRISPR database led by Joe Bondy-Denomy. In green, the anti-CRISPRs we found against Cas9. CRISPR-Cas systems are first divided into two classes based on which enzymes they use to cleave DNA or RNA sequences. In Class 1, this is actually a complex of several enzymes. In class 2, a single, but much larger enzyme is responsible for the final action. The layout of the tree is roughly based on the most conserved CRISPR-Cas gene, Cas1, and colored in deep purple.

The Idea

Back in 2015 I was working on detecting anti-HIV protease small molecules in metagenomic libraries using genetic circuits. Around that time genetic circuits were described that had a CRISPR-Cas output. Back then, CRISPR-Cas was not widely used in genetic circuits. We combined these concepts to find genes in metagenomic libraries that can inhibit a CRISPR-Cas system. Theoretically, it was possible because anti-CRISPRs against CRISPR-Cas type I-F and I-E were found in a ubiquitous bacteria, Pseudomonas aeruginosa. However, no anti-CRISPRs were known for use against the widely-used type II, better known as CRISPR-Cas9. This came in December 2016.

Until now, anti-CRISPRS were found computationally or by cloning out phage genes individually. We sought to perform the anti-CRISPR search in a high-throughput manner and without the prior knowledge that is needed for in silico prediction. The bacterial selection system we used contains two components, as outlined in the figure below.

The primary component is a genetic circuit with a Cas9 protein and guide RNA. This circuit cuts an antibiotic resistance gene on a plasmid, rendering the bacterial cells susceptible to antibiotics when no anti-CRISPR protein is present. The second component in the selection system is an anti-CRISPR source, in this case a metagenomic library. As input material we used metagenomic libraries that were constructed from fecal samples from humans, cows and pigs. Additionally we also used a metagenomic library from a soil sample. I previously wrote how similar systems are used to find new antibiotic resistance genes or vitamins transporters.

The discovery workflow starts with fecal samples from humans, cows and pigs, and a soil sample. It  ends with a list of potential anti-CRISPR genes. The proteins encoded by the potential anti-CRISPR genes were then validated using various experimental methods. 

The Experiments

After a lot of tweaking, colonies appeared that were able to dodge the selection system (and potentially Cas9 activity). Instead of sequencing individual colonies with Sanger sequencing, we used Nanopore sequencing. For Nanopore sequencing we used our previously published poreFUME protocol that allowed us to multiplex the sequencing of colonies and various different DNA sources.

The resulting sequences contained hits that did not only inhibit Cas9 activity, but also contained antibiotic resistance genes or genes that turned off expression of Cas9. After removing these false-postive genes, and to validate whether the sequences are actually inhibiting Cas9, the DNA was re-cloned into an E. coli expression vector. The individual proteins were tested in two ways: by assaying if Cas9 can still cleave DNA, and by testing whether the potential anti-CRISPR protein actually worked.

We visualized this process by putting the resulting reaction on a gel and checked whether the DNA was still intact, indicating that an anti-CRISPR protein was potentially inhibiting Cas9. If the DNA was cut into two pieces it was assumed the protein did not prevent Cas9 from cutting the DNA.

In the second experiment we tested with biolayer interferometry whether the potential anti-CRISPR protein can bind to Cas9. Together these experiments led us to believe that we found four new anti-CRISPR proteins, which we named AcrA7, AcrA8, AcrA9 and AcrA10. (Acr = anti-CRISPR. A because Cas9 is a type II-A system and 7-10 because of the chronological order they were found in, as proposed).

We unleashed a whole suite of computational analyses to find out how widespread these new anti-CRISPR proteins are. For example, we expected that the anti-CRISPR genes would co-occur with the CRISPR-Cas systems they are inhibiting, however there appeared no specific correlation between the two. A possible explanation could be that anti-CRISPR genes are often on mobile elements (such as plasmids and phages) and move through the population more rapidly than CRISPR-Cas systems. However, we did find homologs of the anti-CRISPRS in seven different phyla, including Firmicutes, Proteobacteria, Bacteroidetes, Actinobacteria, Cyanobacteria, Spirochaetes, and Balneolaeota, with high sequence similarity. This hints that the anti-CRISPR genes were moved recently by horizontal gene transfer. 

Overall this was a very exciting research project, though we never optimized this selection system to find all of the possible anti-CRISPRs, nor did we analyze all the resulting clones extensively. We were initially just interested whether this setup could actually work to find new anti-CRISPR genes. I’m confident the anti-CRISPRs found thus far will eventually find their way into mainstream usage of CRISPR-based therapies and applications. Next, it will be exciting to look into more metagenomic libraries against all the other CRISPR types for which we don’t have a single anti-CRISPR yet. I’m sure they are out there!

Uribe, R. V, van der Helm, E., Misiakou, M., Lee, S., Kol, S., & Sommer, M. O. A. (2019). Discovery and Characterization of Cas9 Inhibitors Disseminated across Seven Bacterial Phyla Short Article Discovery and Characterization of Cas9 Inhibitors Disseminated across Seven Bacterial Phyla. Cell Host and Microbe, 25, 1–9. https://doi.org/10.1016/j.chom.2019.01.003




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New paper out: functional metagenomics powered by synthetic biology

Why do functional metagenomics and synthetic biology (or synbio) make such an interesting combination? This week, our new article in Nature Chemical Biology, ‘The evolving interface between synthetic biology and functional metagenomics’, sheds light on how progress in synthetic biology can advance, and already have advanced, the field of functional metagenomics.

We are facing a growing and aging world population, and mankind thus needs new drug molecules and ways to produce nutrients. Instead of using chemical synthesis, drugs and nutrients can be sustainably produced by modified bacteria. Moreover, most of those interesting molecules are already produced by billions of bacteria in the environment. Unfortunately, it is difficult to grow most types of bacteria in a laboratory, and it is therefore not possible to harness their useful capabilities directly. However, bacteria contain all the information needed to produce these valuable molecules in their DNA. Using methods known collectively as ‘functional metagenomics,’ the DNA of these bacteria can be recovered from the environment and used by host bacteria that can be cultivated in a lab. This allows us to make use of the capabilities of the billions of bacteria that are present in the environment without actually growing them, but by directly utilizing their DNA instead.

Construction of a metagenomic library. Environmental DNA is extracted, purified, fragmented and cloned into a shuttle vector. The library of plasmids is then transformed into an expression host such as Escherichia coli. Finally, the resulting clones can be analyzed according to their genotype and/or phenotype.

Which kind of metagenomics should be used?

In practice, there are two ‘metagenomic’ approaches, sequence-based approaches (where environmental DNA is sequenced and a function is assigned computationally) and function-based approaches (where the environmental DNA is transformed into a host bacteria and the genes are expressed and interrogated). In our article, we focused on the functional approach by specifically interrogating metagenomic DNA functionally using a genetic circuit.

The term “metagenomics” can refer to many different techniques and procedures. In our new article, we focused on using genetic circuits to functionally mine a metagenomic library.

In our publication, we first surveyed the ways in which genetic circuits have been used in the recent past to interrogate metagenomic libraries. Though scientists have been quite creative, researchers need to move from a ‘screening’ method to a more high-throughput interrogation methods. These ‘screening’ methods require researchers to painstakingly examine each bacterial colony for a visual change associated with the production of a compound, for example. In more effective high-throughput methods, researchers couple the production of a compound of interest to the survival of the cell. The spontaneous death of cells lacking the target compound replaces the labor-intensive process of scrutinizing massive number of clones. My colleague Hans has utilized this approach previously to identify new vitamin transporters as outlined in the illustration below.

Example of a genetic circuit consisting of a riboswitch coupled with two selectable markers, which can be used to mine a metagenomic library for vitamin B1 transporting or producing genes. The genetic switch can also be formalized as an AND-gate with vitamin B1 as the input and cell survival as the output.

Insights for improving genetic selection circuits can also be obtained from biocontainment research, as it is notoriously difficult to perform experiments in which all cultured cells commit suicide. For example, the research group led by Farren Isaacs showed how multi-layered circuits can aid in this, and a recent review from the Collins lab summarizes the latest advances in biocontainment systems.

We anticipate that the expansion of synthetic biology tools, such as automated circuit design and computational design of proteins, will usher in greater efficiencies in the mining of functional metagenomics libraries. These advances in functional metagenomics and synthetic biology are already demonstrating remarkable potential in industrial and medical applications. Our full paper, available at Nature Chemical Biology, goes into more depth on all the previously constructed genetic circuits and new technologies that will continue to propel the field forward:

van der Helm, E. Genee, H.J. Sommer, M.O.A (2018) ‘The evolving interface between synthetic biology and functional metagenomics’ Nature Chemical Biology 10.1038/s41589-018-0100-x

Other resources

Gallagher, R. R., Patel, J. R., Interiano, A. L., Rovner, A. J., & Isaacs, F. J. (2015). Multilayered genetic safeguards limit growth of microorganisms to defined environments. Nucleic Acids Research, 43(3), 1945–54. https://doi.org/10.1093/nar/gku1378 [-]

Genee, H. J., Bali, A. P., Petersen, S. D., Siedler, S., Bonde, M. T., Gronenberg, L. S., Sommer, M. O. A. (2016). Functional mining of transporters using synthetic selections. Nature Chemical Biology, 12, 1015–1022. https://doi.org/10.1038/nchembio.218 [-]

Lee, J. W., Chan, C. T. Y., Slomovic, S., & Collins, J. J. (2018). Next-generation biocontainment systems for engineered organisms. Nature Chemical Biology, 14(6), 530–537. https://doi.org/10.1038/s41589-018-0056-x [-]

Nielsen, A. K., Der, B. S., Shin, J., Vaidyanathan, P., Densmore, D., & Voigt, C. A. (2016). Genetic circuit design automation. Science, 352(6281), 53–63. https://doi.org/10.1126/science.aac7341 [$]

Taylor, N. D., Garruss, A. S., Moretti, R., Chan, S., Arbing, M., Cascio, D., Raman, S. (2016). Engineering an allosteric transcription factor to respond to new ligands. Nature Methods, 13(2), 177–183. https://doi.org/10.1038/nmeth.3696 [-]

Note: parts of this blogpost are sourced from my PhD thesis

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SynBioBeta ’16 packed with innovation

sblogoLast Wednesday the SynBioBeta conference got kicked off at Imperial College. Central topic was the current state of synthetic biology and how (commercial) value can be gained by supplying tools and platforms. In the keynote by Tom Knight from Ginkgo Bioworks, and the afterwards chat with his old PhD student Ron Weiss (now professor at MIT), a few interesting points came by that illustrate the path synbio has taken over de last two decades.

Ginkgo Bioworks founder Tom Knight

Ginkgo Bioworks founder Tom Knight (Photo courtesy of Twist Bioscience)

Tom started of with a quote from Douglas Adams  “if you try and take a cat apart to see how it works, the first thing you have on your hands is a non-working cat” to illustrate the current (or not so far in the past) state of biology in general. He used the old ‘systems engineering’ of a Boeing 777 example to highlight where synbio should be going in his opinion. As in: 1. design using CAD 2. build 3. it works. So no more tinkering and endless design-build-test cycles. In order to do so he argued for an extra loop in the cycle, the simulate component. This would allow the end-user to design and simulate a layout before actually building and testing it.  However, he was quickly to note that we are currently lacking a lot of insights into the biology of a single simple cell, for exmample the Mycoplasma mycoides of which 149 of the 473 remain of unknown function but are essential for cell survival.

An improved version of the design cycle proposed by Tom Knight

An improved version of the design cycle proposed by Tom Knight

Also the VSLI analog was brought up and the panel noted that Voigts group last week came a step closer to this paradigm by rationally designing circuits and building them.

On the questions whether synbio is progressing fast enough Ron Weiss replied that it is not “as fast as we want”, he recalled the last chapter of his thesis describing a synthetic biology program language, which he laughingly categorized as “completely useless back then”. However the state of mind back in the 2000’s was “that within a year or 5” we would be able to build circuits with at least 30 gates (Voigts paper from last week showed a ‘Consensus circuit’ containing 12 regulated promoters). Tom was a bit more optimistic saying that “You overestimate what is going to happen in 5 and underestimate what happens in 10 years”. Bottom line was the central need to be able to make robust systems that can work in the real world and in order to do so more information is needed such as whole cell models. The session ended with a spot-on question from riboswitch pioneer Justin Gallivan, now at DARPA; “who is going to fund research this research to gain basic knowledge?”. For example, who is going to elucidate the function of the 149 proteins of unknown functions? One suggestion was that Venter should just pull out his checkbook again…

The investors’ perspective

Next on the program was the investors round table geared towards the commercialization aspect of synthetic biology. It was debated whether the use of the term ‘synbio’ would negatively affect your final product or whether it would boost sales, Veronique de Bruijn from IcosCapital argued that the “uneducated audience will definitely judge you” so she suggested to use the term ‘synbio’ cautiously. Business models, an ever debated topic, stroke more consensus among the investors, they all agreed that it is difficult for a platform technology to go out, hence it can be extremely difficult to apply the technology to the optimal specific product. Karl Handelsman from Codon Capital noted that when you do have a product company it is important to engage with customers early, so you build something they really want. Related to this he recalled that a product company at the West Coast typically exits for 60-80 million USD, so you should be aware that you can never raise more than ~9 mUSD throughout the lifetime of a company. When it came to engaging with Corporate Venture Capital, the panel unanimously appraised them for their expertise came, but care should be taken that your exit strategies are not getting limited by partnering up with them. The session was rounded off with a yes/no on the positive impact of Trump as president on synbio, only Karl was positive because this would definitely direct lots and lots of funding towards Life-On-Mars projects.

Applications of synbio by the industry

In the ‘Application Stack’ session five companies pitched their take on synbio and how this can be used as a value creator. Ranging from bacterial vitamin production by Biosyntia to harnessing the power of Deinoccocus. Particular interesting was Darren Platts’ talk who showing one of Amyris in-house developed tools on language specification in synthetic biology. The actual challenge here was not to write the software “pretty straightforward”, it was more difficult to get the users engaged in the project and adapting the tool. Their paper was published recently in ASC Synbio and the code is soon released on Github.

Is there place for synbio in big pharma?

The final session of the first day was titled ‘ Synthetic Biology for Biopharmaceuticals’ and here if found the talks of Marcelo Kern from GSK and Mark Wigglesworth from AstraZeneca especially interesting, they gave their ‘big pharma’ view on how to incorporate synthetic biology into the established workflows. GSK for example focused on reducing the carbon footprint by replacing chemical synthesis with enzyme catalysis. Another great example was the use of CRISPR to generate drug resistant cell lines to for direct use by the in-house screening department.

The first day was rounded of by Emily Leproust from Twist Bioscience, announcing that they would be happy to take new orders from June (!) on.

The future of synbio

The second day started of with a discussion on ‘Futures: New technologies and Applications’ by Gen9 CEO Kevin Mundanely and Sean Sutcliffe from Green biologics. Both showed examples of partnering by their company with academic institutions to get FTO into place. Sean also made an interesting comment that it took them about 4 years to commercialize “technology from the ’70” so he estimated it would take around 12 years before the CRISPR technology, now trickling into the labs, can be used on production scale in the fermenters.

A fun-and-fast-paced ‘Lightning Talks’ session gave industry and non-profit captains a platform of exactly 5 minutes to pitch their vision. Randy Rettberg gave a fabulous speech about the impact of iGEM on the synbio sector and concluded that iGEM helps cultivating the future leaders of the field. Gernot Abel from Novozymes highlighted a ‘citizen science’ project where the ‘corporate’ Novozymes worked together with biohacker space Biologigaragen in Copenhagen to successfully construct an ethanol assay. Along these lines Ellen Jorgensen from the non-profit Genspace pitched their “why a new generation of bio-entrepreneurs are choosing community labs over incubators/accelerators” at a price point of 100$/month versus 1000$/month. Dek Woolfson (known for his computationally designed peptides and cages) gave an academically tasting talk about BrisSynBio but finished his pitch that they are looking for a seasoned business person to help making their tools available for a broader public.

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Dek Woolfson was one of the few (still) academics on stage. (Photo by: Edinburgh iGEM)

What happens when synthetic biology and hardware meet?

The hardware and robot session showcased, among others, Biorealize who are constructing a tabletop device to transform cells and incubate and lyse them, Synthase who just released an open source data management platform Antha and Bento Lab (currently running a very succesfull kickstarter campaign) highlighting their mobile PCR workstation. An interesting question was posed at the end as to how much responsibility Bento Lab was putting on the DNA oligo synthesis companies by democratizing and making PCR available to the general public. Bento Lab defended that they are supplying an extensive ethical guide with their product and that they don’t supply any reagents. Unfortunately this very interesting discussing was terminated due to a tight conference schedule.

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Tabletop transformations, incubations and lysis in one go using Biorealize

A healthy microbiome using GMO’s?

In the final session of SynBioBeta a few examples of synbio applied to the microbiome came by. Boston based Synlogic is planning on starting the IND (Investigational New Drug) process on their E.coli equipped with ammonia degrading capabilities to combat urea cycle disorder. Xavier Duportet showed an example of Eligo Bioscience using CRISPR systems delivered by phages that selectively kill pathogens, such as Staphylococcus aureus, part of this exciting work was published in 2014 in Nature Biotech using mice models.

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Eligo Bioscience and their CRISPR-delivered-by-phage technology (Photo by: Edinburgh iGEM)

After all these dazzling applications of synthetic biology, captain John Cumbers wrapped up SynBioBeta by also announcing the next event in San Fransico at 4th-6th October and in London next year again around April.

Personally I think the conference did a great job at gathering together the industrial synthetic biology community, from both early start-up to big pharma. Although the sentiment is that we are not as far as we want to be, there have been some considerable advancements over the last 15 years. From an investors perspective there is still a lot of uncertainty surrounding the run-time (and the inherently coupled rate of return) of synbio projects, however the recent numbers on VC funding are indicating there is an eagerness to take the leap. Taking together, a jam packed two days with high end exciting synthetic biology applications, it will be very interesting to see if Moore’s law also applies to synbio.

Disclaimer: The above write up is strongly biased by my own interests, so revert to the twitter hashtag #SBBUK16 to get a more colorful overview of the past two days.

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Highlights of the International Synthetic and Systems Biology Summer School 2014

sicily_etnaLast week I joined the International Synthetic and Systems Biology Summer School in Taormina, Italy and as the title describes it was all about Synthetic and Systems biology with some pretty cool speakers.  Weiss talked about the general principles of genetic circuits and the current limitations (record is currently 12 different synthetic promoters in 1 designed network). Sarpeshkar focused on the stochastic nature and the associated noise of cells, he showed how they can be simulated or mirrored using analog circuits. Paul Freemont took Ron Weiss’ design principles and showed how to apply them on different examples, he also elaborated on an efficient way of characterizing new circuits and parts. Tanja Kortemme, a former postdoc from the Baker lab, gave an introduction to the capabilities of computational protein design and using some neat examples showed the power (and limitations) of computational design. Below some highlights and the relevant links of the literature that was discussed.

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On promoters and operators, which combination is the best?

DNA helix artistPromoters and (their often forgotten partner-in-crime) operators are two key elements in the transcription of a protein sequence. A promoter sequence recruits the RNA polymerase and the status of the operator determines whether or not the adjunctive protein sequence gets translated (Figure 1). So far, biochemistry 101. Far more interesting is the diversity in promoter/operator complexes currently employed in the biotech industry and their associated efficiency rates. Not a lot of quantitative and  real comparable research had been done on this topic, until March 2013…

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