The spokesman said the attorney general's office had received requests between June 2018 and January 2019 for "mutual legal assistance" from Brazilian prosecutors relating to their probe.
Brazilian prosecutors have alleged that executives of the commodities companies, including some in the United States, were involved in improper payments to executives at Brazil's state-run oil firm Petroleo Brasileiro SA.
The U.S. Justice Department has launched its own investigation into these business dealings.
The attorney general's spokesman added the requests concerned "in particular two of the three companies mentioned, as well as several natural persons (individual people). These requests are still being executed." He did not identify the two companies or the individuals.
Brazilian federal prosecutors and the trading firms did not immediately respond to a request for comment.
Vitol and Glencore have previously said they are cooperating with Brazilian authorities, and Trafigura has said it takes the allegations seriously. All three have been suspended from business dealings with Petrobras.
In December last year, Brazilian prosecutors alleged the three firms and others collectively paid at least $31 million in bribes over a six-year period to Petrobras officials to secure advantages in deals.
The announcement marked a new phase in the years long "Car Wash" corruption probe that has toppled presidents in two countries and sent more than 130 politicians and businessmen to jail across Latin America.
Swiss, U.S. and Brazilian authorities have worked closely on Car Wash cases that led to the world's largest ever leniency deal after industrial conglomerate Odebrecht agreed to pay $2.6 billion.
The Swiss attorney general announced in November 2016 that it had opened a criminal probe into a Trafigura employee as part of a wider investigation into suspected corruption at Petrobras.
The spokesman said that investigation was ongoing, without providing an update.
(Reporting by Julia Payne; Editing by Mark Potter)
By Julia Payne