A recent update on the VFS website indicates that the U.S. Consulate in Kolkata would be closed on Thursday, September 15, 2011 and September 16, 2011 and again from Monday, October 3, 2011 to Tuesday, October 11, 2001.
U.S. visa applicants planning to appear for a visa interview in Kolkata need to plan their visit to Kolkata based on the above information.
This link can be found here.