From Microbial Warfare to Biotech Revolution: The Hunt for the Next CRISPR

On Earth, a war that has raged for billions of years has never ceased. It unfolds in the microscopic world invisible to us—in the depths of the oceans, within the soil, and even inside our own bodies. The belligerents areAn estimated 10^38 bacteria and an even more vast army of viruses (bacteriophages)This is not the plot of a science fiction novel, but a survival race unfolding in every corner of the Earth.

In this endless arms race, bacteria have evolved a variety of remarkable defensive weapons. They cleave viral components, depriving viruses of the essential elements needed for replication, and even sacrifice themselves to protect neighboring cells. In response, viruses continuously evolve countermeasures, creating a cycle of escalating offense and defense. This process of mutual adaptation has shaped one of the oldest and most complex immune systems on Earth.

Remarkably, although microbiologists have only just begun to grasp the full scope of this ancient war, microbial immune mechanisms have already given rise to revolutionary biotechnologies. From restriction endonucleases, which ushered in the era of molecular biology in the 1970s, to CRISPR-Cas gene-editing technology, which transformed the entire paradigm of biological research in the early 21st century, these world-changing tools all originate from bacterial defense systems.

And now, scientists are searching this vast toolkit for the next discovery capable of sparking a technological revolution. Eugene Koonin, an evolutionary biologist at the U.S. National Library of Medicine, asserts:“I dare say that bacteria and archaea employ every conceivable method of defense—and some you can’t even imagine.”

In fact, the first major contribution of microbial immune mechanisms to human biotechnology dates back to the 1970s, long before the now widely recognized CRISPR technology. At that time, scientists discovered that bacteria could produce a special protein—Restriction Endonuclease, it can cleave DNA at specific sites. Originally a weapon used by bacteria to shred the DNA of invading viruses, this protein has unexpectedly become the key to unlocking the era of molecular biology for humanity.

The discovery of restriction endonucleases was epoch-making. With these enzymes, scientists were finally able to precisely cut and splice DNA fragments, making possible the creation of genetically modified organisms, DNA fingerprinting, gene cloning, and recombinant DNA technology, thereby laying the foundation for modern genetic engineering. More importantly, this discovery led scientists to realize that the defense systems evolved by bacteria in their struggle against viruses might harbor even more world-changing technological secrets.

The story of CRISPR’s discovery began with a seemingly unremarkable observation. In 1987, Japanese scientists identified unusual repetitive sequences in the genome of Escherichia coli, but their significance was not understood at the time. It was only later that researchers realized the DNA fragments within the spacers of these sequences originated from bacteriophages, suggesting that bacteria were essentially recording information about viruses that had previously attacked them, akin to maintaining a wanted poster archive. In 2007, Rodolphe Barrangou of North Carolina State University and Philippe Horvath, a scientist at the Danish food company Danisco, experimentally confirmed that CRISPR indeed functions as an immune system, enabling bacteria to recognize and destroy the genomes of specific viruses.

The true technological breakthrough occurred in 2012. Jennifer Doudna of the University of California, Berkeley, and Emmanuelle Charpentier of the Max Planck Institute in Germany published landmark research demonstrating thatThe CRISPR-Cas9 system can be programmed to cleave any specified DNA sequence.This means that scientists have gained an unprecedented capability:Precise deletion of specific genes, correction of pathogenic mutations, and insertion of new gene functions.

Compared with traditional gene-editing methods, CRISPR is simpler, cheaper, and more precise, and the impact of this discovery has been explosive. It has not only attracted billions of dollars in investment but also earned the two discoverers the Nobel Prize in Chemistry in 2020.

It is no exaggeration to say that,The advent of CRISPR technology has fundamentally transformed the landscape of biological research.It has opened up new avenues for treating genetic diseases, provided new tools for crop improvement, and even made it possible to eradicate disease vectors.The first CRISPR therapy has been approved for the treatment of sickle cell disease and β-thalassemia, marking the formal transition of gene editing from the laboratory to clinical practice.

But this is only the beginning; scientists believe that CRISPR represents just the tip of the iceberg in the vast treasure trove of microbial defense systems.

In simple terms, the CRISPR-Cas system functions like a pair of molecular scissors equipped with GPS navigation. First, the guide RNA carries information about the target sequence, acting akin to a wanted poster. Then, guided by the RNA, the Cas protein scans the entire genome to locate the matching sequence. Once the target is identified, the Cas protein cleaves the DNA double helix like scissors. Finally, the cell’s endogenous DNA repair mechanisms are activated, allowing scientists to seize this opportunity to insert new genetic sequences or delete harmful fragments.

This seemingly simple and elegant system requires an additional recognition sequence as an auxiliary component, which scientists refer to asPAM Sequence. This short DNA fragment helps the Cas protein accurately locate and bind to the target DNA, ensuring that other similar sequences are not mistakenly targeted. It is this precise recognition mechanism that enables CRISPR to find the correct editing site within the vast genome.

In practical applications, CRISPR has demonstrated significant value across multiple fields.

In terms of medical treatment,In addition to the approved therapies for sickle cell disease and beta-thalassemia, researchers are developing immunotherapies for cancer by editing immune cells to more effectively attack tumors, while also exploring gene therapy approaches for viral infections such as HIV.

In the agricultural sector,Scientists use CRISPR to breed disease-resistant crops, enhance their nutritional value, and enable them to adapt to climate change and extreme environments.

At the level of basic research,CRISPR has accelerated functional genomics research, enabling scientists to rapidly elucidate gene functions, create more accurate animal models of disease, and conduct in-depth investigations into the role of genes in evolution.

However, CRISPR is not flawless.Off-target effects remain a persistent issue——Cas proteins sometimes cleave sites that are similar to but not the intended target sequence, which may lead to unintended genetic alterations.

Delivery challenges also pose a significant hurdle; effectively delivering the CRISPR system to target cells in vivo, particularly in hard-to-reach organs and tissues, remains a bottleneck constraining its clinical application.The limitation of the PAM sequence means that not all desired editing sites can be recognized by Cas9, which restricts the flexibility of the technology to some extent.

Furthermore, ethical controversies surrounding human embryo editing have never subsided. Questions such as where the boundary lies between therapeutic and enhancement editing, and whether germline editing should be permitted, continue to plague the scientific community and society at large.

It is precisely these limitations and challenges that drive scientists to continue seeking new tools and solutions within microbial defense systems.

In 2011, Eugene Koonin, Kira Makarova, and their colleagues discovered that immune genes in bacterial and archaeal genomes tend to cluster into “defense islands.” This finding implies that scientists can use known defense genes as markers to search for novel defense mechanisms in their vicinity. This discovery served as a crucial clue on a treasure map, significantly accelerating the identification of new defense systems and laying the foundation for the next world-changing tool.

Driven by advances in the study of defense islands, the results have been astonishing. In recent years, researchers have reported hundreds of potential defense genes. Rotem Sorek of the Weizmann Institute of Science in Israel noted that his research team needs to discuss five new papers every week, yet still cannot cover all the findings. Artem Isaev from the Center for Molecular and Cell Biology in Moscow also lamented that discoveries are emerging so rapidly that researchers do not even have time to discuss all the progress.

Behind this research fervor lies scientists’ anticipation of discovering the next world-changing tool.

Shockingly, researchers are gradually coming to realize thatMany bacterial defense systems exhibit striking similarities to the immune mechanisms of humans and plants.Philip Kranzusch of Harvard Medical School, while studying the human immune protein cGAS, serendipitously discovered that bacteria also possess a system with strikingly similar structure—CBASS。These two systems are not only similar in structure but also nearly identical in their mode of operation.: They can all detect foreign DNA, generate the same signaling molecules, utilize the same receptor protein STING, and ultimately trigger cell death to prevent the spread of infection. Similar discoveries have followed in quick succession; scientists have identified bacterial versions of gasdermin proteins, prokaryotic versions of viperin proteins, and others, indicating that eukaryotes and prokaryotes employ similar defense strategies.

Aude Bernheim from the Pasteur Institute in Paris pointed out, “From an evolutionary perspective, this is completely unexpected.” Scientists originally believed that in the face of continuous viral attacks, the immune system should evolve rapidly, leading to significant differences in defense mechanisms between prokaryotes and eukaryotes. However, the reality is quite the opposite. The defense systems that evolved in the common ancestor of prokaryotes and eukaryotes have persisted for billions of years, creating parallel biological mechanisms across life forms.

Based on these findings, a series of new tools with the potential to challenge or complement CRISPR are emerging. Each tool possesses distinct characteristics and demonstrates unique advantages in different scenarios.

First is the Argonaute system,This is an immune response initially discovered in eukaryotes, and analogous versions have since been identified in microorganisms. Daan Swarts from Wageningen University in the Netherlands has conducted in-depth research on this system, revealing several significant advantages. First, unlike CRISPR, the Argonaute system does not require a PAM sequence, making it more flexible than CRISPR and capable of targeting a wider range of genomic locations. Second, it requires shorter guide sequences, which not only reduces manufacturing costs but also makes the entire system easier to produce and apply. The diagnostic test developed by Swarts’ team, based on the SPARTA system, can detect any target sequence through color changes or fluorescence. Swarts confidently stated, “Basically, any type of sequence can be detected using these Argonaute systems; we have not yet encountered any limitations.” From a commercial perspective, Argonaute offers another important advantage: while CRISPR patents are already saturated, the Argonaute field presents greater opportunities for securing new patent protection.

Next is the TIGR-Tas system,This CRISPR-like system was discovered by Professor Feng Zhang of the Broad Institute of MIT and Harvard. TIGR-Tas, short for Tandem Intergenic Guide RNA–TIGR-associated protein, employs a two-component design to detect specific DNA sequences, similar to CRISPR. However, it does not require a PAM sequence, enabling more flexible programmable cleavage. More importantly, the components of TIGR-Tas are more compact and smaller in size than those of CRISPR. This feature is particularly valuable in gene therapy, as one of the current major limitations is the limited cargo capacity of delivery systems. Adeno-associated virus (AAV) vectors, serving as the primary delivery tool, have a fixed loading capacity; thus, a smaller editing system can be more easily delivered into tissues, offering new possibilities for overcoming delivery bottlenecks.

Next is the Retron system,This genetic element, discovered in the 1980s, had its immune function confirmed only in 2020. Seth Shipman of the Gladstone Institutes at the University of California, San Francisco, recognized the unique value of retrons in gene editing. Retrons use reverse transcriptase to create DNA from an RNA template, enabling the mass production of single-stranded DNA copies within cells. They employ a sophisticated toxin-antitoxin mechanism: the single-stranded DNA product, linked to the RNA template, folds into a double helix that forms a cage sequestering the toxin. If phage enzymes attempt to modify this DNA structure, it triggers a conformational change that releases the toxin, thereby eliminating the infected cell. For CRISPR gene editing, delivering large amounts of DNA templates has long been a challenge; however, with the retron system, scientists can enable cells to mass-produce template copies internally. Shipman has successfully used this method to edit bacteria, yeast, human cells, and phages, and has co-founded a company to advance the technology’s development.

In addition to these editing tools, the counterattack weapons of viruses have also brought new application ideas.

Joseph Bondy-Denomy of the University of California, San Francisco, discovered in 2011 while still a graduate student thatAnti-CRISPR Proteins——A Phage Weapon Capable of Shutting Down the Bacterial CRISPR Defense System.More than 100 Anti-CRISPR protein families are currently known, each operating through distinct mechanisms: some bind to Cas proteins to prevent DNA binding or cleavage, others modify or cleave guide RNAs, and still others interfere with the assembly of CRISPR complexes. These “off switches” provide new means for fine-tuning gene editing. Because Cas enzymes often cleave not only target sites but also similar off-target sites, and because targeted editing is fastest and most effective, scientists can use weakened Anti-CRISPRs or delay their activity to promptly halt Cas enzyme activity once the intended edits are complete, thereby preventing most undesirable off-target editing. Bondy-Denomy’s startup, Acrigen Biosciences, is developing this approach for gene therapy to enhance treatment safety and precision.

The medical application potential of these new tools is particularly exciting.

Many bacterial defense mechanisms adopt a self-destructive strategy, thwarting viral invaders by disrupting their own essential processes; thus, these mechanisms may serve as a source for novel antibiotics. Bondy-Denomy describes this as a gold mine of antibacterial enzymes.CBASS systems, gasdermin proteins, retron systems, and other toxin-antitoxin systems could all be engineered into antimicrobial weapons.The challenge lies in the fact that these systems evolved intracellularly; therefore, it is necessary to develop methods for delivering them into bacteria or for activating endogenous defense systems within bacteria that are present but remain inactive.

Locus Biosciences, based in Morrisville, North Carolina, has adopted an ingenious strategy: they engineered bacteriophages carrying an antimicrobial CRISPR system that, rather than targeting viruses, directs bacteria to destroy their own essential genes. In a small clinical trial for urinary tract infections in women, this therapy successfully reduced pathogen levels and alleviated symptoms, demonstrating the feasibility of repurposing microbial defense systems into therapeutic agents.

Phage therapy itself will also benefit from these studies. Asma Hatoum-Aslan of the University of Illinois Urbana-Champaign cautions, “Once we initiate phage therapy, we will face the issue of phage resistance. The key is to understand this in advance and incorporate certain interventions into our phage therapy regimens.” A deeper understanding of microbial defense systems will help scientists predict and prevent the emergence of bacterial resistance, design more effective phage therapies, and develop combination treatment strategies, thereby revitalizing this ancient therapeutic approach in an era of increasingly severe antibiotic resistance.

Bacterial defense systems that parallel the human immune system point to new avenues for treating autoimmune diseases, cancer, and infections. Transcription-blocking molecules produced by prokaryotic viperin could be developed into antiviral drugs. Kranzusch speculates that signaling molecules generated by the CBASS system could be engineered into vaccine adjuvants to enhance the body’s response to vaccines. Furthermore, research published last year by Bondy-Denomy and colleagues demonstrated that Anti-CBASS proteins can silence the cGAS-STING pathway in human cells, potentially yielding anti-inflammatory effects and opening new pathways for the treatment of autoimmune diseases. Bernheim and other microbiologists are forging collaborations with human immunologists to explore how these immune mechanisms, spanning different forms of life, can inform one another and serve human health.

The integration of artificial intelligence and machine learning is also accelerating progress in this field. Preprint studies published this year show that both the Bernheim laboratory and Michael Laub’s team at MIT are using machine learning to identify new candidates for defense systems. Machine learning can analyze vast amounts of genomic data, predict protein structures, and identify new defense islands, greatly accelerating the screening process for candidate systems. Laub’s assessment is encouraging:“Thousands of new systems remain to be discovered.”This means that what we are currently seeing may represent only a small fraction of the vast repertoire of microbial defense systems.

CRISPR has demonstrated that microbial defense systems can serve as powerful biotechnological tools. Scientists are now building a more diverse toolkit, with each tool offering unique advantages and specific applications.

First, as a mature technology, CRISPR-Cas continues to play a pivotal role in the field of precise gene editing, while Argonaute systems offer more flexible application possibilities due to their PAM-free nature. The compact size of TIGR-Tas makes it particularly suitable for gene therapy delivery; Retron systems enhance editing efficiency through internal DNA synthesis; and Anti-CRISPR proteins provide new means for fine-tuned regulation and improved safety. As Koonin stated, “It is a very high bar to do better than CRISPR, but some of these systems indeed hold significant applications.”

The development pathway in this field is becoming increasingly clear. The journey from basic discovery to clinical application involves multiple stages, including the identification of novel defense systems, elucidation of their mechanisms of action, engineering into laboratory and clinical tools, optimization of efficiency and safety, and ultimately, regulatory approval for clinical deployment.Each stage requires collaboration across different disciplines, which is why future breakthroughs will increasingly rely on multidisciplinary integration.

Computational biology is playing an increasingly important role in this process.Through genomic data mining, scientists can identify novel defense systems from vast repositories of microbial genomes. The advent of protein structure prediction technologies, particularly artificial intelligence tools such as AlphaFold, has facilitated a deeper understanding of the molecular mechanisms underlying these defense systems. Phylogenetic analysis further enables researchers to trace the origins and evolutionary trajectories of these defense mechanisms, shedding light on why certain mechanisms have been conserved over billions of years.

Synthetic biology provides tools for the engineering and optimization of these natural defense systems.Scientists are no longer content with simply using systems found in nature; instead, they are beginning to design new defense mechanisms, optimize the performance of existing tools, and even create hybrid systems that combine the advantages of different tools. This rational design approach is accelerating the translation process from discovery to application.

The needs of clinical medicine provide clear direction for these studies.Personalized gene therapy requires more precise and safer editing tools. The development of precision diagnostic tools necessitates technologies capable of rapidly and specifically detecting target sequences. The exploration of novel antibacterial strategies requires an understanding of how bacteria defend against viral attacks, as well as how to harness these mechanisms as weapons against pathogenic bacteria.

Meanwhile, we must not overlook the ethical and social challenges posed by these powerful technologies.Advancements in gene-editing capabilities have blurred the line between therapeutic and enhancement editing. The formulation of regulations for germline editing requires striking a balance between scientific possibilities and social ethics. Safety assessments for releasing engineered microorganisms into the environment must take into account long-term ecological impacts. Issues of technology accessibility are also becoming increasingly prominent: how to ensure equitable access to these advanced therapies in developing countries, how to control costs to make them affordable, and how to promote technology transfer rather than exacerbate global health inequalities are all critical questions that demand careful consideration and resolution. As we acquire powerful technological capabilities, we must also cultivate corresponding sense of responsibility and forward-thinking.

The billions-of-years-old war between bacteria and viruses has provided humanity with a seemingly inexhaustible source of innovation. From restriction enzymes to CRISPR,The numerous emergingNew systems are pushing the boundaries of biotechnology with every discovery. The rapid development in this field is breathtaking, with new findings emerging so quickly that even researchers struggle to keep pace.

Although no single technology appears poised to completely supplant CRISPR as the most transformative biological discovery of this century, this does not signal the end of exploration. On the contrary, we are witnessing the dawn of a new era—one characterized by a diverse toolkit, where each tool delivers unique value in specific scenarios.

These findings also remind us of a profound truth: nature has spent billions of years conducting the most exquisite engineering design.Our task is not to innovate from scratch, but to learn to read and understand nature’s vast engineering manual.

In this sense, the search for the next CRISPR is not merely a scientific question but a philosophical proposition:How can we find answers to humanity’s most modern problems in nature’s oldest struggles? How can we harness its wisdom to serve human well-being while respecting nature? How can we maintain reverence for ethical boundaries while pursuing technological advancement?The answers to these questions will be written jointly by this generation and the next. And the very process of writing them is the most exhilarating manifestation of human intellect.