A biomass plant in the U.S. state of Texas has shut down while authorities are investigating a bomb threat, local media reported on Wednesday.The threat was found written on the inside wall of a portable toilet at the Southern Power biomass plant in Nacogdoches County, in east Texas, on Monday evening, according to local TV channel KYTX.The company decided to close the facility until after Thanksgiving even though a deadline on the note had passed by several hours when it was found, local newspaper Daily Sentinal quoted a police officer as saying.Thomas Kerss, the Nacogdoches County sheriff, told the newspaper the bomb threat is taken seriously because a power plant is a national security interest.The shutdown will lead to a loss of 1.1 million U.S. dollars, Kerss said.The sheriff also said that his department obtained the warrant on Wednesday afternoon and is searching for the suspect, whose name had not been released.The suspect will be charged with a third-degree felony of disorderly conduct.