An attorney from the public defender's office appointed to represent Dutschke declined to comment after Monday's hearing. Another attorney of Dutschke's, Lori Nail Basham, said she will continue to represent him in other matters but not in the federal case.
Dutschke's house, business and vehicles in Tupelo, Miss., were searched last week, often by crews in hazardous materials suits, and he had been under surveillance.
He faces up to life in prison if convicted. A news release from federal authorities said Dutschke was charged with "knowingly developing, producing, stockpiling, transferring, acquiring, retaining and possessing a biological agent, toxin and delivery system, for use as a weapon, to wit: ricin."
He already had legal problems. Earlier this month, he pleaded not guilty in state court to two child molestation charges involving three girls younger than 16, at least one of whom was a student at his martial arts studio. He also was appealing a conviction on a different charge of indecent exposure. He told The Associated Press last week that his lawyer told him not to comment on those cases.
Earlier in the week, as investigators searched his primary residence in Tupelo, Dutschke told the AP, "I don't know how much more of this I can take."
"I'm a patriotic American. I don't have any grudges against anybody. ... I did not send the letters," Dutschke said.
Dutschke and Curtis were acquainted. Curtis said they had talked about possibly publishing a book on a conspiracy that Curtis says he uncovered about the black-market sale of body parts. But he said they later had a feud.
Curtis's attorney Hal Neilson said the legal team gave authorities a list of people who may have had a reason to hurt Curtis and Dutschke's came up.