Microbes in blood are closely related to each other (and to us); this knowledge can help treat diseases

Paramananda Barman July 17, 2017


In a recent study, a group of researchers at the Indian Institute of Engineering Science and Technology (IIEST) Shibpur, exploring the evolutionary relationship between various strains of microbes in the human blood using their protein sequences, found that not only are these organisms related to each other, but that they have genetic similarities with humans.

This is a significant finding, which can help us prevent or fight diseases like Type 2 diabetes and cardiovascular illnesses.

But wait, microbes in our blood? Yes, it’s not just the human gut but human blood too which has rich microbial diversity, and this plays an important physiological role. Blood microbiome (or the lack thereof) could lead to health issues; for instance, the presence of H. pylori, a bacterium, in blood could contribute to Parkinson’s disease. The researchers hope that their study, published in the journal Molecular Phylogenetics and Evolution, could pave the way for efficient treatment of such diseases.

When Antonie van Leeuwenhoek designed the first microscope, little did he know that he would show us an exciting world of microbes. Since the 1670s, technology has progressed tremendously, opening up a treasure trove of information on microbes like viruses, bacteria and archaea (single-celled organisms with no cell nucleus or any other membrane-bound organelles in their cells). While we harbour about 100 trillion microbes in our body, we have so far listed close to 3000 microbes for genome sequencing under the ‘Human Microbiome Project’, an initiative by National Institutes of Health (NIH), USA.

A sketch of the microscope by Van Leeuwenhoek from his book ‘Arcana Naturae Detecta’ published in 1695. Image: commons.wikimedia.org

While we despise these microbes as ‘germs’, scientists give it a fancy name — the ‘human microbiome’ – an ecosystem of sorts that harbours microbes. But not all of them are ‘germs’ or cause diseases; some provide vitamins, and a few guide our immune system to detect harmful invaders and produce compounds to fight against disease-causing microbes too. Probiotics, the science of using friendly bacteria like Lactobacillus, Bifidobacterium, and Streptococcus, carries tremendous health benefits. In fact, statistics say that the total number of microbes in our body is 10 times higher than the total number of cells in our body, and the total number of genes in the human microbiome is 200 times higher than total genes present in our genome!

A few scientists have found this world of microbes so exciting that they believe understanding this microbiome from different parts of our body could reveal promising outcomes, which can then be used for disease control. Studies have shown that a change in the skin microbiome can lead to psoriasis, atopic dermatitis and acne, variations in the gut microbiome have been related to eczema, asthma and food allergies. Now, it is practically possible to replace ‘harmful bacteria’ with ‘friendly, useful’ bacteria to address infections.

A close-up of Red Blood Cells (RBCs) in human blood

“Human microbiome analysis has drawn immense interest because of its promise in understanding biological systems at a deeper scale,” says Dr. Malay Bhattacharyya, one of the authors of the study done at IIEST, Shibpur. The comprehensive study of blood microbiome would undoubtedly change the landscape of how we understand diseases originating in the blood, says the researcher. “This kind of tissue-specific analysis of the microbiome is of high interest for therapeutic purposes too,” he adds.

While previous studies have tried to establish an evolutionary relationship between gut bacteria, this study focuses on looking at the microbes in our blood.

For this study, the researchers collected protein sequence information from the ‘Human Microbiome Project’ and conducted a phylogenetic study of 22 common proteins found in human blood microbiome. A phylogenetic study compares DNA or protein sequence information to draw conclusions about the evolutionary relationship among different species.

A phylogenetic study compares DNA or protein sequence information to draw conclusions about the evolutionary relationship among different species.  

Interestingly, the phylogenetic analyses conducted by the IIEST researchers revealed that different sister groups of microbes in our blood are also evolutionarily connected to each other. For instance, the bacterial species Enterococcus faecium that causes neonatal meningitis, and Enterocococcus faecalis that causes urinary tract infections, showed strong similarity to each other.

But how close are these microbes to humans? To explore this, the researchers analysed 22 of the commonly found microbiome proteins in humans and found 5 of them to be occurring in humans AND microbes. To their surprise, they found that many microbes did exhibit some similarity with human proteins, with members of the genus Enterococcus showing the highest co-existence with humans in most cases. The sequence similarities are found to be comparatively much higher for the proteins like peptide deformylase and thymidylate synthase. Interestingly, all these evolutionary conserved proteins are found to have closely related functions.

But how close are these microbes to humans?  

What is the importance of studying the blood microbiome? Dr. Bhattacharyya says: “The study on microbiomes has significant implications in the areas of environmental microbiology and medical microbiology. The understanding of human microbiology and its surrounding microbes is tightly coupled to the environment.” Research in microbiology is not merely confined to the diagnosis, prognosis and treatment of diseases — rather, it also involves the study of helpful microbes. Therefore, microbiome analysis is supportive to the combat against many diseases and promotes their treatment, says the researcher.

“Since the microbiome has been shown to have an impact on the physiology of the host in far-reaching ways, knowledge about microbes constituting the microbiome is significant”  

“Since the microbiome has been shown to have an impact on the physiology of the host in far-reaching ways, knowledge about microbes constituting the microbiome is significant,” comments Prof. S. Mahadevan, Professor at the Department of Molecular Reproduction, Development and Genetics, Indian Institute of Science, Bengaluru. Similarities between proteins of the microbe and the host suggest the possibility of gene exchanges between the two by a process known as horizontal gene transfer. This is a recently recognised aspect of evolution, says Dr Mahadevan.

As scientists figure out innovative ways to understand diseases and design better strategies to fight them, a renewed hope lingers on for a disease-free world.

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Update on July 17 at 5.30 pm: First paragraph of the story has been edited for clarity.
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