remove white space

[eluser]Bigil Michael[/eluser]
i want to remove the white space between words

i used validation like this

Code:

array('field'   => 'username','label'   => 'Username', 'rules'   => 'trim|required|xss_clean'),

it accepts username like this bigil michael

i want to remove the white space between bigil & michael

i searched,but no result
can anyone help me????
thanks in advance...........