Can a 555 output be made to pull to ground?
You can use CMOS version of IC 555 (LM555,.. for example). It will swing down to ground and up to VCC.

Or you can do this :







simulate this circuit &ndash; Schematic created using CircuitLab

Vcc depends on your MCU voltage and M1,M2 should be logic-level MOSFETs.