For those who haven't already read this book Alanna Collen's Book is a good start on the significance of microbes for human health [1] https://www.amazon.com/10-Human-Microbes-Health-Happiness/dp...

I got to know about microbiome sometimes last year.

Spent good amount of time on reading about it, some books I read:

* 10% Human: How Your Body’s Microbes Hold the Key to Health and Happiness (https://www.amazon.in/10-Human-Microbes-Health-Happiness/dp/...)

* Gut: The Inside Story of Our Body's Most Under-Rated Organ (https://www.amazon.in/gp/product/938528861X)

* Brain Maker: The Power of Gut Microbes to Heal and Protect Your Brain–for Life (https://www.amazon.in/dp/0316380105)

also watched the course on Coursera about Microbiome (https://www.coursera.org/learn/microbiome), it was an eye opener.