Before starting to read this article, could you please take a minute to depict a bacterium? Oily capsule? Long and zigzagged flagella? Wired and irregular shape? Yes, indeed, ever since its appearance being observed under the microscope, bacteria have been assimilated as a foe that humans need to combat. But did you know that most bacteria in the world are actually friendly and beneficial to humans? It seems that humans and bacteria have reached a harmonious relationship as bacteria could exist everywhere in the human body: in the gut, on the skin and in the mouth. It sounds disgusting, doesn’t it? But do take a deep breath and calm down. Rather than harming you, bacteria actually “collaborate” with you, they had hosted in your body since few hours after birth, trying their best to keep you and them alive. From biological terms, this phenomenon is referred to as symbiosis. If bacteria are unhappy with their “accommodation”, they raise the alarm in a special way: you probably will feel as unhappy as they do. That is to say, your mental health would go wrong somehow.
With more than a billion estimated bacteria in the world (Sender, Fuchs & Milo, 2016) , no man in the world could ever get rid of bacteria. Since bacteria account for such a proportion in the human body, it is definitely not surprising that the human genome is largely dependent on the Guangmiao Jin, Chengyue Tao.bacterial genome. In many cases, diseases induced by bacteria imbalance in the gut can be highly similar to the neural disease in terms of symptoms. For example, depression is characterised by weight loss and less active immune system which also be found patients suffering from gastrointestinal tract disorder. With more studies being carried out to investigate how bacteria can actually influence brain functioning, three major factors are revealed: hormone, neurotransmitter and immune cells. Bacteria co-live in the same extracellular matrix as body cells do, therefore, gut bacteria constantly scan the surroundings to guarantee that they are growing in a favourable environment for them to proliferate. If not, they will transfer this information to brain cells so that brain cells can proceed and respond to the information by adjusting the amount of hormone secreted. As beneficial bacteria are attacked by harmful microbiomes or do not grow in the correct way, the homeostasis is interrupted due to hormonal imbalance. Moreover, bacteria are involved in neurotransmitter manufacturing procedure to some extent, either explicitly or implicitly, like producing dopamine directly or regulating the serotonin synthesis indirectly. Neurotransmitter enables communication between neuronal cells by delivering information through chemical signals. Consequently, if the neurotransmitter concentration is too low or too high it may have direct repercussions upon naturally occurring pathways in humans. For example, people could be extremely sensitive because their neurons over-react to external stimuli. Last but not the least, bacteria abnormality would worsen the immune system response to pathogens, causing severe physical and mental problems. (Butler et al., )
Since the hypothesis of bacteria-induced chemical changes to the central neural system is prevalent among scientists, numerous researches were developed. The experiment conducted by Neufeld, Kang& Foster in 2010 on mice model is one of the most resounding studies. It shows how gut germ is related to anxiety-like behaviour and change of central neurochemical in mice. In this experiment, researchers compared the basal behaviour of adult germ-free (GF) mice and conventionally reared specific pathogen (SPF) mice by conducting two behaviour tests. For starters, a Locomotor test which monitored the moving distance of each mice was carried out. Unfortunately, data collected from this test did not show any obvious difference between the two groups. In another behaviour test——Elevated plus-maze test, which was based on animal nature of being reluctant to stay in the open space, the mice were placed on plus-maze space(figure 1) to test how they react. The more time the mice spent on enclosed arms, the greater the anxiety it had. Statistical analysis of the experimental results proved that GF mice spent less time on open arms than SPF mice, which means GF mice were more anxious. (Lalonde & Strazielle, 2008) Apart from the two behaviour tests, the expression of BDNF mRNA had also been tested as converging lines of evidence, because the expression of BDNF mRNA is directly proportional to anxiety level. Therefore, the GF mice were divided into two groups. Half of them remained in the GF cage and the rest were housed with SPF mice. The GF mice in mixed housing can gain bacteria because bacteria flora from SPF mice can colonize into the gut of GF mice. In the end, the expression of BDNF mRNA from GF mice was measured again, revealing the fact that the mixed housing GF mice expressed less BDNF mRNA. In other words, after gaining bacteria, the anxiety of GF mice was reduced. From this experiment, behavioural and chemical evidence proved that GF mice, in comparison to SPF mice, appeared more anxious. (Neufeld et al., 2011)
Even though no clear mechanism on bacteria-brain communication was highlighted, there is high evidence that keeping bacteria healthy is crucial to mental health, especially your gut bacteria which play a significant role in the digestion system. Here are some small tips for Imperial students to look at to help keep their gut bacteria healthy:
1. Maintaining a healthy diet
Generally, abundant and diverse gut flora is considered to be healthy. Each species relies on varied food resources. Since we are unsure of the specific nutrition required by every strain, the most secure thing we can do is to take a balanced diet to trigger diverse bacterial growth.
2. Uptake of prebiotics in the diet
Prebiotics promote the growth of “friendly” bacteria in the human gut (GIBSON et al., 1995). Try to have more food rich in prebiotics, such as oats, onions, nuts and leeks.
3. Do more physical exercise
One study showed that professional rugby players have a 2-fold increase of gut flora species as compared to controls of similar body size, age and gender (Clarke et al., 2014).
Why not proactively join the sports activities organised by college union?
As you can see, bacteria strive as hard as any Imperial student does and also share the same nutrients and oxygen as your own cells. Feeding bacteria well allows you better mental condition which benefits you in every aspect from study to life. Are there any reasons for you not to cherish and love them after reading the article?