The genome of Streptomyces scabies, the predominant causal agent of potato common scab, encodes a potential cutinase, the protein Sub1, which was previously shown to be specifically induced in the presence of suberin. The sub1 gene was expressed in Escherichia coli and the recombinant protein Sub1 was purified and characterized. The enzyme was shown to be versatile because it hydrolyzes a number of natural and synthetic substrates. Sub1 hydrolyzed p-nitrophenyl esters, with the hydrolysis of those harboring short carbon chains being the most effective. The V max and K m values of Sub1 for pnitrophenyl butyrate were 2.36 mol g -1 min -1 and 5.7 10 -4 M, respectively. Sub1 hydrolyzed the recalcitrant polymers cutin and suberin because the release of fatty acids from these substrates was observed following the incubation of the enzyme with these polymers. Furthermore, the hydrolyzing activity of the esterase Sub1 on the synthetic polymer polyethylene terephthalate (PET) was demonstrated by the release of terephthalic acid (TA). Sub1 activity on PET was markedly enhanced by the addition of Triton and was shown to be stable at 37°C for at least 20 d.

The outer potato periderm layer consists of dead suberized cells. Suberin, a protective biopolymer, is made of a polyaliphatic portion covalently linked to polyaromatic moieties. Evidence accumulates that Streptomyces scabies, the main causal agent of potato common scab, can degrade the suberin aliphatic part but its ability to degrade the aromatic portion has not been documented. This polyaromatic portion is mainly composed of cinnamic acids. In this study, two cinnamates (trans-ferulic or p-coumaric acids) were added to the culture medium of S. scabies strains EF-35 and 87.22. HPLC quantification revealed that both strains efficiently utilized these compounds. A proteomic study coupled with gene expression analysis led to the identification of putative catabolic pathways for cinnamates. Catabolism of both compounds appeared to occur via the β-ketoadipate pathway. Gene SCAB_15301, encoding for a putative vanillate monooxygenase, was partly deleted from S. scabies strain 87.22 genome. The mutant retained its ability to catabolize trans-ferulic acid into vanillate but lost its ability to further degrade the latter compound. When the wild-type mutant and complemented strains were grown in the presence of suberin-enriched potato periderm, accumulation of vanillic acid was observed only in the mutant culture medium. This work presents evidence that S. scabies can degrade not only the aliphatic part of suberin but also the constituents of suberin aromatic portion. This may provide ecological and pathological advantages to S. scabies as a saprophyte and pathogen.

Numerous studies investigated the possibility of incorporating plastic wastes in concrete mixtures, thus contributing to efficient management and sustainable development of the construction industry. This paper investigates the possibility of reducing the water-to-cement ratio and/or incorporating steel fibers or polymeric latexes to mitigate the drop in structural properties of reinforced concrete (RC) beams containing polyethylene terephthalate (PET) additions. The PET was derived from waste plastic bottles that were shredded into small pieces and added during concrete batching at 1.5% to 4.5%, by total volume. Test results showed that the concrete plain and structural properties degrade with PET additions, given their lightweight nature and poor characteristic strength compared to aggregate particles. The reduction of w/c from 0.55 to 0.46 proved efficient to refine the matrix porosity and reinstate the shear and flexural strengths of RC beams. Moreso, the incorporation of 0.8% steel fibers (by volume) or 15% styrene-butadiene rubber latexes (by mixing water) were efficient to enhance the bridging phenomenon and reduce the propagation of cracks during beam testing.