How do bacteria find food? It is an important question as everything and also bacteria need to intake food/nutrients to survive and grow.
Think about how you get food. First of all you realise that you are hungry, then you need to know where your next food source is, which can be either your fridge or the nearest take away, and then you move towards it.
Bacteria do it very similarly.
Interestingly, most bacteria can move or swim towards a nutrient as soon as they are hungry and they know where to find food.
This process of bacterial movement according to a chemical is called chemotaxis. Such chemicals can be nutrients like sugars, amino acids, nitrogen or oxygen among others like metals, hormones or neurotransmitters. A chemical that activates bacterial movement is called a chemoeffector.
The movement can be towards or away from the chemoeffector depending on whether the chemoeffector is good or bad for the bacterium.
Chemotaxis is a highly regulated mechanism because moving the whole bacterial cell costs a lot of energy. Just as you have to be very hungry to drag yourself up the sofa to move towards the fridge 😉
So how does all of this work? Yes, there is a figure.
First of all, a bacterial cell has to know that it is hungry which means it is missing a certain nutrient as in our figure sugar (in blue).
To know what is going on in the environment, bacteria have different chemoreceptors on their cell surfaces (in purple). These chemoreceptors contain two parts: one half sits at the outside of the cell while the other half is placed on the inside and both parts are connected through the bacterial cell membrane.
On the outside the chemoreceptor can bind the specific chemoeffector when it is present in the environment. This binding activates the chemoreceptor which is illustrated by the star in the figure.
On the inside of the cell the chemoreceptor is bound to a sensor protein (in red). This one is responsible to sense the signal; which in this case is when the chemoeffector is present in the environment. So the sensor protein gets activated when the receptor binds the chemoeffector on the outside.
This sensor protein then activates its partner, the response regulator (the purple pacman). This one is responsible to respond to the incoming signal.
When activated, the response regulator binds to the flagellum of the bacterium (the long appendix of the bacterium). The flagellum is a fascinating little machine and can be understood as a little rotor with a propeller. There are amazing videos of bacterial flagella on youtube.
Binding of the response regulator activates the flagellum and it starts spinning which moves the bacterium.
This movement is regulated so that the bacterium can be going towards or away from the chemoeffector. So with this bacteria can move towards the nutrient source or away from a dangerous or toxic chemoeffector.
Interestingly, bacteria do not only use chemotaxis to find nutrients. When they arrive within the human body or a plant they can also sense certain hormones or even neurotransmitters. In such case, the bacterium realises that it is indeed within a human body or plant and close to a human cell and it swims towards it. Then it can produce all their virulence factors and properly infect the cell and thus the body.
In any case, chemotaxis helps bacteria to survive either by finding nutrients or by helping them to infect cells and grow in them.
Take away from this week’s article:
- bacteria use chemotaxis to know that they are surrounding by specific chemicals
- presence of the chemical activates their flagellum which allows them to swim
- they can swim towards the chemical if it supports bacterial growth or away if it is damaging