In the 18-minute recorded conversation, whose authenticity NDTV cannot verify, Nirmala Devi, an assistant professor with Devanga Arts College, is seen talking to women students and allegedly trying to persuade them for sexual favours to unnamed top university officials in exchange for academic and monetary favours.
She is heard telling four of her students about a video of the governor that she had shot in a meeting.
"In that meeting, you can see the close quarters from where I was able to film. It's not allowed. But now I have the allowance to move much closer. There is no screen now, at the governor level," Nirmala Devi is heard saying in the audio clip.
"Unfortunately the tape mentions the governor's name and those in proximity. Caesar's wife must be beyond suspicion. But the governor organises a press meet to exonerate himself. We want a CBI probe, no man can be a judge for his own cause," said DMK Spokesperson A Saravanan.
On Wednesday, the governor called a press conference and denied having met the professor. He also ordered a probe by Santhanam, a retired bureaucrat.
"I don't know the lady and I have not met her. What else you want? There is no need for a CBI probe. When it is needed, I would be the first to order," Mr Purohit had said.
The girls had complained to college authorities a month ago after which the professor was suspended. She was arrested earlier this week. A five-member probe committee announced by Madurai Kamaraj University to which the college is affiliated was withdrawn after the governor ordered a probe.
"The governor's behavior is unacceptable. He usurped the power of the university and the vice-chancellor. What was the need for hurriedly calling a press conference on an issue the government should act," asked DMK working president MK Stalin.
The alleged 'sex for degree' scandal has been handed over to the crime branch. The state government has so far been silent over the opposition's allegations against the governor.