How autocorrect username type in wp mu registration ?

in wp username can only lowercase and no space or symbol

my market usually don’t know and use space and or symbol to their username registration

is there any solution that make auto correct for their input

example :

1. when they type “my username” then automatically became “myusername”

2. when they type “my.username” then automatically became “myusername”

or any idea in this issue?