Polyester degradation by soil bacteria: identification of conserved BHETase enzymes in Streptomyces.

The rising use of plastic results in an appalling amount of waste which is scattered into the environment. One of these plastics is PET which is mainly used for bottles. We have identified and characterized an esterase from Streptomyces, annotated as LipA, which can efficiently degrade the PET-derived oligomer BHET. The Streptomyces coelicolor ScLipA enzyme exhibits varying sequence similarity to several BHETase/PETase enzymes, including IsPETase, TfCut2, LCC, PET40 and PET46. Of 96 Streptomyces strains, 18% were able to degrade BHET via one of three variants of LipA, named ScLipA, S2LipA and S92LipA. SclipA was deleted from S. coelicolor resulting in reduced BHET degradation. Overexpression of all LipA variants significantly enhanced BHET degradation. All variants were expressed in E. coli for purification and biochemical analysis. The optimum conditions were determined as pH 7 and 25 °C for all variants. The activity on BHET and amorphous PET film was investigated. S2LipA efficiently degraded BHET and caused roughening and indents on the surface of PET films, comparable to the activity of previously described TfCut2 under the same conditions. The abundance of the S2LipA variant in Streptomyces suggests an environmental advantage towards the degradation of more polar substrates including these polluting plastics.

Enhanced surface colonisation and competition during bacterial adaptation to a fungus.

Bacterial-fungal interactions influence microbial community performance of most ecosystems and elicit specific microbial behaviours, including stimulating specialised metabolite production. Here, we use a co-culture experimental evolution approach to investigate bacterial adaptation to the presence of a fungus, using a simple model of bacterial-fungal interactions encompassing the bacterium Bacillus subtilis and the fungus Aspergillus niger. We find in one evolving population that B. subtilis was selected for enhanced production of the lipopeptide surfactin and accelerated surface spreading ability, leading to inhibition of fungal expansion and acidification of the environment. These phenotypes were explained by specific mutations in the DegS-DegU two-component system. In the presence of surfactin, fungal hyphae exhibited bulging cells with delocalised secretory vesicles possibly provoking an RlmA-dependent cell wall stress. Thus, our results indicate that the presence of the fungus selects for increased surfactin production, which inhibits fungal growth and facilitates the competitive success of the bacterium.

Protoplast-mediated transformation of Madurella mycetomatis using hygromycin resistance as a selection marker.

Madurella mycetomatis is the main cause of mycetoma, a chronic granulomatous infection for which currently no adequate therapy is available. To improve therapy, more knowledge on a molecular level is required to understand how M. mycetomatis is able to cause this disease. However, the genetic toolbox for M. mycetomatis is limited. To date, no method is available to genetically modify M. mycetomatis. In this paper, a protoplast-mediated transformation protocol was successfully developed for this fungal species, using hygromycin as a selection marker. Furthermore, using this method, a cytoplasmic-GFP-expressing M. mycetomatis strain was created. The reported methodology will be invaluable to explore the pathogenicity of M. mycetomatis and to develop reporter strains which can be useful in drug discovery as well as in genetic studies.