Ismael “El Mayo” Zambada, the notorious alleged co-founder of the Sinaloa Cartel, pleaded not guilty to US drug charges on Friday after he and a son of a Mexican drug lord were arrested in Texas in a dramatic achievement for US law enforcement that could usher in a seismic shift to Mexico’s criminal landscape. Court records showed that Zambada directed that a not guilty plea be entered on his behalf, which was accepted by US Magistrate Judge Anne Berton. At an initial court appearance in a Texas courtroom on Friday,…