Introduction

Microorganisms including bacteria, fungi and viruses—can make you ill and cause infectious diseases such as ‘flu and measles but they can also be beneficial to health by defending the host against pathogens and boosting immune system responses. A good example of this is the microbiome found in the gastrointestinal tract (GIT). Presence of this complex population of different microorganisms and metabolites ensures the breakdown and absorption of important nutrients from ingested substances and produces chemicals that shape metabolic rates and overall metabolic health. Recent research has shown that some Bacillus spp. in the digestive tract can bind to immune cells and stimulate them to divide and reproduce, providing a boost in immune response. In this section, a brief historical view of microbiology (the study of microorganism) and the diversity of microorganisms will be covered.