What type of bacteria is $Rhizobium$?

Which of the following is a recently discovered Gram-positive,non-leguminous,nitrogen-fixing bacterium?

Give scientific reasons:
$(1)$ Leguminous plants are rich in protein.

Trace the events starting from the coming in contact of Rhizobium to a leguminous root till nodule formation. Add a note on the importance of leghemoglobin.

Arrange the stages of root nodule formation in the correct sequence:
$I-$ Infection thread is produced.
$II-$ Bacteria are carried to the cortex of the root.
$III-$ Bacteria attach to the root hair.
$IV-$ Bacteria are released from the thread into the cells.
$V-$ Differentiation into nitrogen-fixing cells occurs.

Nodules with nitrogen-fixing bacteria are present in