Background

Yarrowia lipolytica is an ascomycetous dimorphic fungus that exhibits biofilm mode of growth. Earlier work has shown that biosurfactants such as rhamnolipids are efficient dispersants of bacterial biofilms. However, their effectiveness against fungal biofilms (particularly Y. lipolytica) has not been investigated. The aim of this study was to determine the effect of rhamnolipid on a biofilm forming strain of Y. lipolytica. Two chemical surfactants, cetyl-trimethyl ammonium bromide (CTAB) and sodium dodecyl sulphate (SDS) were used as controls for comparison.

Results

The methylene blue dye exclusion assay indicated an increase in fungal cell permeability after rhamnolipid treatment. Microtiter plate assay showed that the surfactant coating decreased Y. lipolytica biofilm formation by 50%. Rhamnolipid treatment disrupted pre-formed biofilms in a more effective manner than the other two surfactants. Confocal laser scanning microscopic studies showed that biofilm formation onto glass surfaces was decreased by 67% after sub-minimum inhibitory concentration (sub-MIC) treatment with rhamnolipids. The disruption of biofilms after rhamnolipid treatment was significant (P<0.05) when compared to SDS and CTAB.

Conclusion

The results indicate a potential application of the biological surfactant to disrupt Y. lipolytica biofilms.

Catheters and other indwelling devices placed inside human body are prone to bacterial infection, causing serious risk to patients. Infections associated with implants are difficult to resolve, and hence the prevention of bacterial colonization of such surfaces is quite appropriate. In this context, the development of novel antimicrobial biomaterials is currently gaining momentum. We describe here the preparation and antibacterial properties of an enzyme-embedded polycaprolactone (PCL)-based coating, coimpregnated with the antibiotic gentamicin sulfate (GS). The enzyme uses PCL itself as substrate; as a result, the antibiotic gets released at a rate controlled by the degradation of the PCL base. In vitro drug release studies demonstrated sustained release of GS from the PCL film throughout its lifetime. By modulating the enzyme concentration in the PCL film, we were able to vary the lifetime of the coating from 33 h to 16 days. In the end, the polymer is completely degraded, delivering the entire load of the antibiotic. The polymer exhibited antibacterial properties against three test isolates: Escherichia coli, Pseudomonas aeruginosa, and Staphylococcus aureus. Foley urinary catheters coated with the modified polymer exhibited sustained in vitro release of GS over a 60-h period. The results suggest that the antibiotic-plus-enzyme-loaded polymer can be used as tunable self-degrading antimicrobial biomaterial coating on catheters.

Competition between species plays a central role in the activity and structure of communities. Stable co-existence of diverse organisms in communities is thought to be fostered by individual tradeoffs and optimization of competitive strategies along resource gradients. Outside the laboratory, microbes exist as multispecies consortia, continuously interacting with one another and the environment. Survival and proliferation of a particular species is governed by its competitive fitness. Therefore, bacteria must be able to continuously sense their immediate environs for presence of competitors and prevailing conditions. Here we present results of our investigations on a novel competition sensing mechanism in the rhizosphere-inhabiting Pseudomonas putida KT2440, harbouring gfpmut3b-modified KanR TOL plasmid. We monitored benzyl alcohol (BA) degradation rate, along with GFP expression profiling in mono species and dual species cultures. Interestingly, enhanced plasmid expression (monitored using GFP expression) and consequent BA degradation were observed in dual species consortia, irrespective of whether the competitor was a BA degrader (Pseudomonas aeruginosa) or a non-degrader (E. coli). Attempts at elucidation of the mechanistic aspects of induction indicated the role of physical interaction, but not of any diffusible compounds emanating from the competitors. This contention is supported by the observation that greater induction took place in presence of increasing number of competitors. Inert microspheres mimicking competitor cell size and concentration did not elicit any significant induction, further suggesting the role of physical cell-cell interaction. Furthermore, it was also established that cell wall compromised competitor had minimal induction capability. We conclude that P. putida harbouring pWW0 experience a competitive stress when grown as dual-species consortium, irrespective of the counterpart being BA degrader or not. The immediate effect of this stress is a marked increase in expression of TOL, leading to rapid utilization of the available carbon source and massive increase in its population density. The plausible mechanisms behind the phenomenon are hypothesised and practical implications are indicated and discussed.