Proof of Claim
To get in line with the tenant's other creditors and hopefully collect some of the back rent, file a proof of claim with the bankruptcy court. You'll need to submit a total of unpaid rent before the tenant filed for bankruptcy. Keep track of the rent due after the bankruptcy filing because the court treats them separately. Inform the court of the tenant's security deposit as well. Depending on how the court chooses to allocate funds, you may get none, part or all of the back rent paid.
http://homeguides.sfgate.com/tenant-filing-bankruptcy-owes-back-rent-53174.html