Fig. 4.

Effects of different antibiotic dosage treatments (0, 50, or 400 mg/L) on gut microbial growth and soybean tolerance in WT- and RR-WCR. (A) Antibiotic treatments (dosage indicated on the left) suppressed growth of culturable bacteria in WT- and RR-WCR guts. Pulverized gut-tissue suspensions (10⁴-fold diluted, 100 µL) were dropped on nutrient agar plates and cultured for 48 h at 30 °C. (B) Survival of WT-WCR (Higginsville, MO, population) and RR-WCR (Shabbona, IL, population) treated with different antibiotic concentrations (mg/L) before feeding on soybean plants. Significant differences (log-rank test, Tukey–Kramer adjusted) between survival curves were declared at P < 0.05 (letters next to the key). Crosses represent WCRs treated with 400 mg/L of antibiotics and fed with corn (CR) during the same experiment. (C) Effects of antibiotic treatments on gut cysteine protease activities in WT-WCR (Higginsville, MO, population) and RR-WCR (Urbana, IL, population). Protease activities are expressed as nanomoles of pNA released per milligram of gut protein per minute. Different letters indicate significant differences between treatments (Fisher’s LSD; P < 0.05).