Recessed beam where joists meet in center of room
Short answer:


Get an engineer to size the beam and end supports and footings.
Lay the beam on top, attach it to the vertical support.
Use long U-shaped joist hangers to hang the joists off the beam.
Demolish the existing wall.
Spend the rest of your life cleaning up.


Long Answer -  2 part Blog post that I wrote after I did a similar reno in my house.