The human body is a pathogen killing machine. We have an incredibly developed
immune system containing a variety of cells capable of binding and “killing” foreign
bacterial cells. Our bodies are in constant contact with bacteria in the air, water, and
soil. In fact, the human body contains roughly 10x more bacterial cells than human
(eukaryotic) cells1. These bacterial cells are incredibly important for human health and
utilization of nutrients and energy from food. Nevertheless, a group at the Nanyang
Technological University in Singapore is designing bacteria which can find and destroy
other potentially pathogenic bacteria.
In an article published 10SEP2013 the group describes reprogramming Escherichia
coli to find and destroy a model pathogenic bacteria Pseudomonas aeruginosa. The
investigators describe two main difficulties for this project; persuading the bacteria to
find the pathogenic bacteria, and providing it with the tools to destroy their target.
Bacteria possess a natural process for moving toward “food” and away from toxins
by rotating their flagella, a long whip-like protein. This process called chemotaxis
is regulated by the ratio of CheZ to CheY proteins which determine clockwise or
counterclockwise movement of the flagella. The E. coli were programmed to sense
the presence of P. aeruginosa using a sensing device developed in a previous project.
However, the natural response for E. coli is to move away from these pathogenic
bacteria, so the researchers reprogramed its chemotaxis behavior by destabilizing
In order for E. coli to fight the pathogenic P. aeruginosa, it needed to be equipped
with a suitable arsenal. P. aeruginosa and other pathogenic bacteria can be difficult to
kill because they often form biofilms (a slimy substance containing a large number of
bacteria with several small molecules like sugars and proteins), which are more difficult
to destroy than a single (planktonic) bacterium. Thus, researchers provided the E. coli
with the biolfilm degrading enzyme nuclease DNAseI. Microcin S was selected as the
antibiotic, because it has been shown to kill efficiently against a wide range of Gram-
negative microbes like P. aeruginosa.
Bacteria already act as part of our immune system by competing for space in and on
our bodies. But the development of bacteria which will actually seek out and destroy
invading microbes could add a new category of safety, compared to our current, passive
In our current healthcare system individuals wait until they feel symptoms of a bacterial
infection. The patient must meet with a doctor who performs tests to determine the
bacterial pathogen, and then provide access to an antibiotic. This study presents
a possible improvement in which bacteria residing in our body will simply kill the
pathogenic bacteria at the first sign of invasion. It is the bacterial equivalent of training an attack dog for protection.
1 Wenner, M. (2007, November 30). Humans Carry More Bacterial Cells than Human Ones. Strange But True.
Retrieved December 11, 2013, from http://www.bhhsnormans.us/ourpages/auto
Chang, MW., et al. (2013) Reprogramming Microbes to Be Pathogen-Seeking Killers. ACS Synthetic Biology.