Enterobacter cloacae is a microbial biocontrol that can suppress seed infection by Pythium ultimum. This phenomenon occurs when E. cloacae metabolizes the chemical cues that are necessary for P. ultimum to infect a germinating seed. However, the depletion of these chemical cues by E. cloacae only occurs when carbohydrates are scarce. Thus, when carbohydrates are abundant in seed exudates P. ultimum will infect the seed even if E. cloacae is present. In this research, we attempt to solve this problem by pairing E. cloacae with other bacterial isolates that are superior competitors for carbohydrate resources. This was done to alter the realized niche of E. cloacae so it would consume fatty acids even in exudates with abundant carbohydrates. We accomplished this by determining the carbon metabolic profile of each isolate. We then paired E. cloacae and a single competitor isolate for competition trials in seed exudates and used the supernatant from these competition trials to determine if P. ultimum suppression occurred. Random forest regression models were used to determine which carbon sources were predictive of P. ultimum suppression. General competition outcomes on pathogen suppression were analyzed using Wilcoxon Rank-Sum test.
Results/Conclusions
Our preliminary results indicate that competition was predictive of P. ultimum suppression and that when a competitor outcompetes E. cloacae on seed exudates that P. ultimum will be suppressed (Wilcoxon Rank-Sum test, p-value = 0.0132). However, surprisingly we also found that none of the common carbon substrates tested were indicative of P. ultimum suppression (Random Forest Regression, p-value = 0.963). Prior work has suggested that the carbohydrates glucose, sucrose, and fructose generally inhibit the suppression of P. ultimum by E. cloacae. Instead, our work indicates that the outcome of competition is important for predicting the function of E. cloacae and that additional mechanistic screening may not be warranted in order to improve E. cloacae function aside from general competition assays.