Which bacteria live symbiotically on the root system of leguminous plants?

Nodulated roots make the plant rich in

Mark the correct sequence of steps for the development of root nodules in legumes:
$a.$ Formation of infection thread.
$b.$ Division of cortical and pericyclic cells.
$c.$ Curling of root hairs.
$d.$ Leghaemoglobin synthesis.

Assertion : Nitrogen-fixing enzyme in legume root nodules functions at low oxygen concentration.
Reason : Low oxygen concentration is provided by leghaemoglobin.

Which bacteria are present in the structure shown below?

Leghemoglobin is found in which one of the following organisms?