Short answers, pulled from the story.
Antonie van Leeuwenhoek is considered a father of microbiology. In 1676, working in Delft in the Netherlands, he directly observed bacteria and other microorganisms using a single-lens microscope of his own design. Louis Pasteur and Robert Koch are also regarded as fathers of modern microbiology and medical microbiology respectively.
Multiple thinkers proposed this independently across centuries. Marcus Terentius Varro warned in ancient Rome that invisible minute creatures floating in air near swamps caused serious diseases. In 1546, Girolamo Fracastoro formally proposed that epidemic diseases were caused by transferable seedlike entities. Robert Koch later proved the germ theory of disease in the 19th century through experimental work.
Athanasius Kircher published his Scrutinium Pestis in 1658, stating correctly that plague was caused by microbes. What he likely saw, however, were red or white blood cells rather than the plague agent itself. He had previously written in 1646 about observing what he described as an innumerable multitude of worms in vinegar and milk.
Less than 1% of the microorganisms present in common environments can be cultured in isolation using current means. This limitation has driven microbiologists toward molecular biology tools such as DNA sequence-based identification, including 16S rRNA gene sequencing for bacterial identification.
Corynebacterium glutamicum is one of the most important bacterial species in industrial biotechnology, with an annual production of more than two million tons of amino acids, primarily L-glutamate and L-lysine.
Mahavira, the founding teacher of Jainism, asserted as early as the 6th century BCE that unseen microbiological creatures lived in earth, water, air, and fire. Jain scriptures describe nigodas as sub-microscopic creatures living in large clusters with very short lives, said to pervade every part of the universe including plant tissues and animal flesh.