Materials and Reagents

1. Cells: Non-transformed E. coli AC70R1-504 or harboring plasmids with the S. mutans glgC and glgD genes, separately or combined
   Note: This strain has a deficient production of the ADP-glucose pyrophosphorylase enzyme in absence of complementary plasmids (Morán-Zorzano et al., 2007).
   
2. Luria-Bertani (LB) liquid medium
   
3. Antibiotics: Kanamycin (US Biological, catalog number: K0010 ) and spectinomycin (Sigma-Aldrich, catalog number: S4014 )
   
4. Inducers: Isopropyl β-D-1-thiogalactopyranoside (IPTG) (Sigma-Aldrich, catalog number: I6758 ) and nalidixic acid (Sigma-Aldrich, catalog number: N4382 )
   
5. Plasmids: pMAB6/glgC, expressing S. mutans glgC (induced by nalidixic acid) and pMAB5/glgD, expressing S. mutans glgD (induced by IPTG)
   Note: These plasmids are compatible and bear resistance to spectinomycin and kanamycin, respectively (Asencion Diez et al., 2013).
   
6. D(+) Glucose (Sigma-Aldrich, catalog number: G5767 )
   
7. Iodine crystals (Biopack Medical, catalog number: 2000162300 )
   

Equipment

1. 1.5 ml microcentrifuge tube (Deltalab, catalog number: 200400 )
   
2. Microcentrifuge (Beckman Coulter, model: 22R )
   
3. Shaker (at least 200 rpm) at 37 °C (Thermo Fisher Scientific)
   

Procedure