I share a unique bond with the bacterium Xanthomonas. During my graduate studies at UC Davis, I focused my thesis on Xanthomonas campestris pathovar campestris, a member of this genus responsible for diseases in brassicas, including cabbage, broccoli, radish, and mustard.

My Ph.D. journey was filled with enjoyable moments both in the lab and socially. I found amusement in sharing my research topic at gatherings, stating with a serious demeanor, “Black rot of cabbage.” The reactions varied from confusion to disgust, and some were just entertained. Witnessing these responses made it all worthwhile.

While my topic may not have sounded as impressive as some of my peers’ work on more glamorous subjects, my humorous introduction successfully piqued interest and allowed me to emphasize the significance of plant disease research.

Understanding plant diseases is critical for agriculture and food security. Gaining insights into their transmission and management is essential for sustaining healthy crops and ensuring food supply for an expanding global population.

Thus, although my study on cabbage black rot might not appear groundbreaking, it plays a crucial role in the broader landscape of agricultural science. Research in this area could potentially lead to significant advancements in the future.

In fact, the bacterium Xanthomonas has contributed to notable scientific innovations beyond plant pathology. Here are three remarkable products and technologies that owe their existence to Xanthomonas:

1. Xanthan gum

Xanthan gum is a high-molecular-weight carbohydrate polymer generated by Xanthomonas. It is a common ingredient in processed foods, serving as a thickener, stabilizer, and emulsifier that enhances texture and stability.

While xanthan gum is popular in the food industry, I must admit I tend to shy away from processed foods, especially those loaded with various industrial ingredients. For instance, xanthan gum is often marketed as a gluten-free substitute. However, for those of us with gluten intolerance, it can cause digestive issues, particularly when derived from a culture medium that includes wheat.

I once purchased a bottled Tomato, Pepper & Cucumber Gazpacho Soup, which seemed healthy but left me bloated and uncomfortable afterward. It turned out that xanthan gum comprised a significant portion of the soup, illustrating how the food industry can mislead consumers into choosing processed items disguised as nutritious options.

Beyond the food sector, xanthan gum finds applications in cosmetics, pharmaceuticals, and even in the oil and gas industry as an additive. The xanthan gum market is experiencing annual growth exceeding 5%, with projections indicating it could reach $1 billion soon.

2. TALEN gene editing technology

TALENs (Transcription Activator-Like Effector Nucleases) emerged in the mid-2000s as a novel gene editing tool. This technology originated from the identification of virulence effector proteins, known as TAL Effectors (TALEs), secreted by Xanthomonas. These proteins represent a unique class of DNA-binding proteins, following a specific code where each protein repeat corresponds to a DNA base.

When I first encountered this technology at a plant pathology conference in 2009, I was astounded by its potential.

Shortly after, researchers began combining TALEs with a DNA-cutting domain from the FokI endonuclease, creating programmable enzymes capable of targeting specific genomic sequences. This fusion of DNA-binding and cutting abilities makes TALENs a potent tool for gene editing, applicable in both medicine and agriculture. For example, in a gene therapy trial, TALENs successfully corrected a mutation in a one-year-old girl with cancer, demonstrating their transformative potential.

Though TALENs have seen some decline in popularity following the rise of CRISPR technology, their applications continue to expand beyond plant-pathogen interactions.

3. The antibiotic albicidin

Albicidin is an antibiotic produced by Xanthomonas albilineans, a pathogen affecting sugarcane. Similar to TALEs, albicidin acts as a virulence factor, promoting the pathogen's infection by inhibiting DNA gyrase, a vital enzyme for DNA replication in plant chloroplasts, ultimately leading to plant cell death. Interestingly, as chloroplasts share evolutionary ties with bacteria, albicidin also shows antibacterial properties, making it a promising therapeutic antibiotic.

Recent studies have reignited interest in albicidin. My colleague Dmitry Ghilarov recently elucidated the structure of albicidin in complex with DNA gyrase and a DNA fragment, revealing how it obstructs the gyrase enzyme's function.

This research presents opportunities to enhance the clinical applications of albicidin and may help mitigate the emergence of antibiotic-resistant bacteria, which can arise from increased gyrase gene copy numbers.

Basic research — The unknown potential of cures

Delving into seemingly odd topics like cabbage black rot can lead to unforeseen scientific breakthroughs. As Nobel laureate Barry Marshall aptly noted about scientific inquiry: “You don’t know where you will end up. You don’t know what you will cure.” In the meantime, let’s continue to engage and entertain others as we underscore the importance of fundamental research and the transformative power of science.

Acknowledgements

This article was created with the support of ChatGPT and Quillbot.

This article is available under a CC-BY license via Zenodo. Cite as: Kamoun, S. (2023). 3 unexpected things we owe to the plant pathogenic bacterium Xanthomonas. Zenodo https://doi.org/10.5281/zenodo.7586037