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Microbial Degradation of Chromium-Tanned Leather During Thermophilic Composting: A Multi-Scale Analysis of Microbial Communities and Structural Disruption
by
, , , , and
Manuela Bonilla-Espadas
1
,
Irene Lifante-Martinez
1,
Mónica Camacho
2
,
Elena Orgilés-Calpena
1,
Francisca Arán-Aís
1,
Marcelo Bertazzo
1,* and
María-José Bonete
2,*
1
Footwear Technological Centre, INESCOP, 03600 Elda, Spain
2
Grupo Biotecnología de Extremófilos, Departamento de Bioquímica y Biología Molecular y Edafología y Química Agrícola, Universidad de Alicante, 03690 San Vicente del Raspeig, Spain
*
Authors to whom correspondence should be addressed.
Biology 2025, 14(12), 1799; https://doi.org/10.3390/biology14121799
Submission received: 12 November 2025
/
Revised: 11 December 2025
/
Accepted: 17 December 2025
/
Published: 18 December 2025
(This article belongs to the Section Microbiology)
Simple Summary
Leather waste, particularly that derived from chromium-tanned leather that generated from chromium-tanned leather, is difficult to manage because it contains both persistent collagen and chromium compounds that can be harmful if not handled properly. In this work, we used thermophilic composting as a controlled laboratory tool to establish a reproducible system in which small pieces of chromium-tanned leather were exposed to the naturally occurring microbiota and the high temperatures typical of this process. Our aim was not to certify that this process already offers a safe final solution for leather waste, but to create a reproducible thermophilic composting environment suitable for characterising the microbial communities that develop in compost in contact with chromium-tanned leather and for isolating some of their members for further research. We combined small (2 L) and larger (40 L) composting systems with DNA sequencing, microscopy and classical microbiology to examine how thermophilic composting conditions affected the leather material and the associated microbiota. The composting conditions led to a marked alteration of the leather structure. They identified bacterial and fungal groups adapted to warm, chromium-rich environments, from which we obtained several cultivable strains. These results provide a first microbiological basis for developing future biotechnological tools to manage chromium-tanned leather waste more safely. However, additional studies are still needed before this approach can be recommended as a routine treatment option in real waste management scenarios.
Abstract
Inefficient chromium (III)–collagen cross-linking during leather tanning generates solid waste and effluents containing residual chromium, raising environmental and health concerns. Biological strategies are increasingly popular for tannery waste treatment, but the microbial communities involved in leather degradation remain poorly understood. This study did not seek to evaluate leather disintegration according to standardised compostability criteria, but to establish a thermophilic composting system suitable for characterising leather-associated microbial communities, biofilm formation on leather and isolating cultivable strains. Composting assays were carried out at two scales, in which wet blue leather was mixed with organic compost under self-heating thermophilic conditions. Temperature was monitored, and mass loss and changes in leather structure were determined by gravimetry and scanning electron microscopy. Bacterial and fungal communities in compost with and without leather were analysed using high-throughput amplicon sequencing. Thermophilic consortia dominated by Firmicutes, Actinobacteria and Ascomycota were established, and several bacterial isolates and a filamentous fungus were recovered. Together, these results provide a first basis for understanding the communities and strains associated with chromium-tanned leather during thermophilic composting, supporting future searches for microorganisms and enzymes of interest for biological strategies to manage chromium-tanned leather waste.
