Bacterial Streamers

Bacterial Streamers

Our research group works at the intersection of biology and the physical sciences, and over the last few years we have done a substantial work on a class of biophysical problems related to bacteria. As you might be already aware, bacteria represent one of the most ancient life forms on our planet. Bacteria are unicellular organisms, and an average bacterium is microscopic in nature. Think of a human hair – a typical bacterium is 1/10th of the size of human hair. Despite their size and the fact that they do not even possess a nucleus, bacteria are capable of a fascinating lifestyle. Like humans, bacteria can live a solitary lifestyle in a liquid environment or they can live in community structures. Bacterial communities, of which there can be different types, usually consist of bacterial cells suspended in a gelatinous matrix of their own secretion. Imagine scores of M&Ms embedded in Jell-O – bacterial communities can be imagined as their microscopic counterpart. Why do bacteria secrete gelatinous matrix in which they themselves can be ‘caught’. The gelatinous matrix actually makes bacterial cells very resilient to external stresses such as antibiotics and can make it very hard for you to scrub off bacterial colonies off surfaces. Thus, community living does for bacteria what it also does for humans – allows us to survive harsh conditions by putting up a collective brave front.
       So, what is our research group doing with bacteria and bacterial colonies? Well it turns out those bacterial communities that grow in environments with sustained fluid flow, can take on the shape of a filament, which is known as a ‘Bacterial Streamer’. ‘Bacterial Streamers’ is a technical name and you would not find this name in a dictionary (yet). Where would you find these streamers? A simple example can be river, where streamers are often seen tethered from one end onto a rock, while the other end freely floats in water. My group works with miniature devices, and we found that streamers can also grow in these small devices over a period of time. The figure below was obtained by Mr. Amin Valiei, who was an MS student in my research group1. In the figure, the bacteria are glowing bright green, the gelatinous matrix enveloping the bacteria is invisible, and black circle are micropillars. When we first discovered the phenomenon, the mechanics of the formation of these were still a mystery. Over the last few years, we have shown that a certain class of bacterial communities called flocs can undergo rubber-like stretching by fluid shear leading to the formation of these streamers2.

       
What makes streamers interesting? It turns out that a bacterial streamer is some ways akin to a spider web. In miniature devices, which abound in biomedical sciences and engineering, these bacterial filamentous structures can ‘catch’ more and more bacteria over time and soon become a web-like structure containing millions and billions of bacteria. Eventually, these can clog the devices leading to their final failure. The figure below shows an image from our research group that was featured on the back cover of the Royal Society of Chemistry journal LabChip. The image shows such a clogging in progress.

          For our work here, we used bacteria that were genetically engineered to glow green. Under a microscope, a mature streamer looks like a galaxy of bacteria. Due to this reason, we propose the name जीवाणु गंगा (jeevanu ganga) for bacterial streamers. The figure below, I have named ‘जिवाणुओं की होली’ (jeevanuaon ki holi). For me, research is a long yatra towards truth. This yatra need not be onerous, but is meant to be enjoyed at every instant.



References & Notes:

1. Valiei, Amin, et al. "A web of streamers: biofilm formation in a porous microfluidic device." Lab on a Chip 12.24 (2012): 5133-5137.

2. Hassanpourfard, Mahtab, et al. "Bacterial floc mediated rapid streamer formation in creeping flows." Scientific reports 5 (2015).

3. Karimi, A., et al. "Interplay of physical mechanisms and biofilm processes: review of microfluidic methods." Lab on a Chip 15.1 (2015): 23-42.

4. Hassanpourfard, Mahtab, et al. "Dynamics of bacterial streamers induced clogging in microfluidic devices." Lab on a Chip 16.21 (2016): 4091-4096.

Acknowledgements: Dr. Kumar greatly appreciates inputs from all his collaborators in his research. In particular, Dr. Ghosh's input on the sanskrit names is acknowledged. 

About the author: Dr. Aloke Kumar is currently an Assistant Professor at the Indian Institute of Science, Bangalore. Twitter handle: @aalokelab

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