Which organisms have been used for human welfare for centuries?

Most of the microorganisms that produce antibiotics live in the soil because:

Consider the following statements:
$I.$ Antibiotics are chemical substances produced by some microorganisms which can kill or retard the growth of other disease-causing microorganisms.
$II.$ Penicillin is the first antibiotic discovered by Alexander Fleming $(1928)$,while working on the bacterium $Staphylococcus$ $aureus$.
$III.$ The function of penicillin as an antibiotic was established by Ernst Chain and Howard Florey.
Which of the statements given above are correct?

$A$ pure culture of bacteria was first obtained by..........

Identify the bacterium from the given options.

Microbes like $Spirulina$ can be grown on materials like:
$I$. Waste water from potato processing plants
$II$. Straw
$III$. Animal manure and sewage
$IV$. Molasses
Choose the correct option.