V. parahaemolyticus can infect humans´ gut, when contaminated raw or insufficiently cooked seafood is consumed. Due to environmental conditions such as increase in water temperatures, the number of cases of intestinal infection is increasing around the globe [1]. Therefore, it is crucial to decipher which factors are contributing to the spread of this pathogenic bug. For me it is fascinating the ability exhibited by bacteria to switch and differentiate into distinct cell types according to the environmental scenario. As estuarine areas are a natural habitat of V. parahaemolyticus, this bacterium can adapt to move not only in liquid but also in solid surfaces. Particularly, as a short swimmer and as an elongated swarmer cell, respectively [2][3]. Although some studies suggested that this bacterium can probably transit from solid to liquid environments due to the tidal rhythms of estuarine areas [4, 5], this hypothesis had never been tested before.  

The discoveries that are present in our article result from at least three main factors. One was the curiosity to test if the transition of cells from solid to liquid indeed happens. The second factor was the interaction with other scientists, either by establishing collaborations or by giving talks and receiving feedback. I collaborated with Dr. Timo Glatter, the head of the new mass spectrometry facility, which joined our institute the same year I did. Timo helped me to obtain and analyze the data from proteomics - a strong, useful tool I used during my research. After I gave a seminar talk, a colleague of mine asked me an interesting question: “Although it is already known that people get severely sick when they ingest contaminated raw seafood, did you ever test if bacteria from a swarm colony (a surface attached colony) can attach to seafood and fish?“ The answer was mainly “no”, and after the talk that idea would just simply not leave my mind. And here comes the third factor: I planned an experiment in which I saw that some cells were released from the swarm colony into the liquid and some cells did attach to chitin – a main component present in seafood organisms. New ideas evolved from here, and my supervisor Dr. Simon Ringgaard and I, kept planning more experiments, which led to the story I am going to tell you now.  

Our studies show that V. parahaemolyticus swarm colonies (colonies grown in solid surfaces) develop over time into a highly structured architecture and consist of zonal regions of specialized and differentiated cells. To further simulate the tidal rhythms of estuarine environments and how these influence the ecology of V. parahaemolyticus, we flooded swarm colonies and analyzed the effect on colony development and if cells were released from colonies during flooding events. 

 Interestingly, flooding had profound effects on colony architecture and we showed that cells were released from the colony into the liquid environment. Surprisingly, we could identify this population of released cells as a novel cell type with a different cell size and a distinct proteome when compared to the populations present in center and periphery of the swarm colonies. We named this new cell type as “adventurer cells”. Particularly, these adventurer cells can explore new niches immediately after flooding, as they can 1) swim efficiently, 2) sense chitin (or in other words “smell potential food”) and swim towards it through a process called chemotaxis and 3) re-attach to new solid surfaces, such as submerged chitin surfaces.      

  What implications do our findings have?

Once these adventurer cells are released into the liquid and attach to the surface of seafood, it means this bacterium enters into our food chain. Additionally, zooplankton, which is a group of marine organisms composed of chitin, may serve as a means of spreading of this bacterium to other coastal areas. V. parahaemolyticus can also infect the gut of shrimps and has been recently appointed as the cause of an early mortality syndrome (EMS) of this marine animal. Adventurer cells would thus be of central importance for the worldwide epidemiology of the disease and to develop measures to contain it - for example in industrial aquaculture. Lastly, the mechanism of spreading we describe here could represent a general mechanism utilized by other swarming pathogenic bacteria, such as V. alginolyticus, which also lives in estuarine and marine waters. But that will be another study, another story…

1.      Ceccarelli D, Hasan NA, Huq A, Colwell RR. Distribution and dynamics of epidemic and pandemic Vibrio parahaemolyticus virulence factors. Front Cell Infect Microbiol 2013; 3: 97

2.      McCarter LL. Dual flagellar systems enable motility under different circumstances. J Mol Microbiol Biotechnol 2004; 7: 18–29.

3.      McCarter L. The multiple identities of Vibrio parahaemolyticus. J Mol Microbiol Biotechnol 1999; 1: 51–57.

4.      Jones JL, Kinsey TP, Johnson LW, Porso R, Friedman B, Curtis M, et al. Effects of Intertidal Harvest Practices on Levels of Vibrio parahaemolyticus and Vibrio vulnificus Bacteria in Oysters. Appl Environ Microbiol 2016; 82: 4517–4522.

5.      Nordstrom JL, Kaysner CA, Blackstone GM, Vickery MCL, Bowers JC, Depaola A. Effect of Intertidal Exposure on Vibrio parahaemolyticus Levels in Pacific Northwest Oysters. Journal of Food Protection . 2016 10: 2178–2182.