Rapid and solitary production of mono-rhamnolipid biosurfactant and biofilm inhibiting pyocyanin by a taxonomic outlier Pseudomonas aeruginosa strain CR1.

Biosurfactant - Rhamnolipids (RLs) and antibacterial toxin - pyocyanin (PYO) produced by Pseudomonas aeruginosa strains have great potential for biotechnological applications. Generally, RLs are produced as a mixture of di-rhamnolipids (di-RLs) and mono-rhamnolipids (mono-RLs). Mono-RLs possess superior emulsification and antimicrobial properties and are costlier than di-RLs. In this study, a taxonomic outlier P. aeruginosa strain CR1 isolated from rhizosphere soil was explored for mono-RLs and PYO production. Phylogenetically strain CR1 resembles avirulent outlier P. aeruginosa strain ATCC9027, lacks archetypical virulence genes and harbors unique pathways for the synthesis of solely mono-RLs and PYO. Strain CR1 produced RL biosurfactant which efficiently emulsified hydrocarbons, showed hemolysis and inhibited Bacillus subtilis. At 37 °C, strain CR1 exclusively produced 21.77 g L-1 and 19.22 g L-1 rhamnolipid in glycerol amended Luria Bertani (LB) medium and basal medium amended with rice bran oil, respectively after 54 h growth. Besides RL production was unaffected under varying nitrogen sources. Structural characterization using FTIR, TLC, and LC-MS confirmed that strain CR1 exclusively produced mono-RLs, majorly dominated by Rha-C10-C10, Rha-C10-C8, and CH3-Rha-C12:2-C10:1. The compound was stable over a wide pH range (4-12), salinity (25%) and 100 °C indicating its applicability under harsh environmental conditions. In addition, strain CR1 produced 4.5 μg mL-1 PYO, which could efficiently inhibit biofilm formation by Bacillus species. The environmental outlier strain CR1 can be used for the industrial production of biotechnologically important mono-RLs and PYO.