S-layer Increases Predation Ability Of Myxococcus Xanthus

Background: Myxococcus xanthus is a gram-negative soil bacterium that exhibits micro-predatory activities. When starved, M. xanthus produces resistant spores within fruiting bodies for survival. The S-layer is a paracrystalline structure intertwined in many different patterns and is composed of proteins or glycoproteins. A species that produces the S-layer is Aeromonas. A. salmonicida is a strain of Aeromonas that infects fish. A. hydrophila is another pathogenic strain that causes a wide range of human diseases. We investigated the ability of the S-layer to protect Aeromonas from predation by Myxobacteria. Methods: Myxococcus and prey Aeromonas cultures were standardized to a concentration of 109 and1010 cells per ml and spotted 1mm apart on partial starvation agar media. Predation assay plates were incubated for up to 72 hours and samples collected at 48 h and 72 h. Fruiting body and sonication-resistant spore counts were performed to determine the number of fruiting bodies and spores formed by M. xanthus under different conditions. Aeromonas strain Ahy1127 (S-layer +) was more susceptible to predation by Myxo. strain DK1622. Aeromonas ATCC7966 (S-layer -) was the least susceptible. All strains showed a decrease in surviving prey cells compared to the control spots. There was a greater difference in number of surviving prey cells after predation when compared to prey only control spots for S-layer plus strain Ahy1127 than for S-layer negative strain ATCC7966. Results: Polymerase Chain Reaction was performed to verify the presence of the S-layer gene in various strains of Aeromonas. Aeromonas strains were grown in Brain Heart Infusion broth at 30°C for 24 h without shaking. Growth of the culture as a sediment was taken as an indication for the presence of the S-layer. Conclusion: The presence of the S-layer appears to enhance the predation ability of M. xanthus. Future directions would be to insert the S-layer genes into a S-layer negative Aeromonas strain such as ATCC7966 and repeat the predation assay. If the strain becomes more susceptible to predation on acquiring the S-layer, this would support the inference that S-layer enhances predation ability of Myxococcus xanthus