Gas chromatography-mass spectrometry and scanning electron microscopy with energy-dispersive radiograph analysis of biodeteriorative metabolites produced by Aspergillus species

Abstract

Background and objectives Fungal deterioration of cultural heritage is a major problem that causes physical and chemical damage as well as esthetic alteration. In the current research, fungal species that exist on a brick sample obtained from Egyptian historical places were isolated and identified. Moreover, various metabolic products produced by the isolated fungal species were detected, which may play an important role in the deterioration of many historical buildings.Materials and methods Various fungi existing on brick samples collected from an Egyptian historical place were identified phenotypically and then confirmed molecularly based on the 18 S rDNA technique. The metabolites found in the chloroform extract of the isolated fungi were detected by gas chromatography-mass spectrometry. Quantitative mineralogical analysis of the deteriorated brick was studied by radiograph diffraction. Moreover, scanning electron microscopy-energy-dispersive radiograph was employed to identify the mineral compositions and surface structural morphology of the collected brick sample.Results and conclusion Three fungi showed the highest occurrence and were identified as Aspergillus niger, Aspergillus terreus, and Aspergillus flavus. The metabolites found in the chloroform extract of the three fungi were detected by gas chromatography-mass spectrometry, which showed that 5­octadecene, (E) was common among A. niger, A. terreus, and A. flavus; nonadecane and E­15­heptadecenal were common between A. niger and A. flavus; α­cadinol, tetradecane, and hexadecane were common between A. niger and A. terreus; and trans­caryophyllene, α­humulene, tau­muurolol, and octadecane were common between A. terreus and A. flavus. In addition, there was a presence of other hydrocarbons and various organic acid esters that play a vital role in the brick deterioration. Moreover, radiograph diffraction and scanning electron microscopy-energy-dispersive radiograph results showed that the brick sample contains Si, Fe, Ca, and Al, with small amounts of Na, Mg, and Cl. The fungal hyphae penetrating the brick sample were also detected. Our results demonstrate that fungi existence could result in physical deterioration by extending their hyphae through the brick pores resulting in stress. Fungi could also lead to chemical deterioration due to the production of different acids and acid derivatives that cause the brick demineralization via chelation of various metal. In addition, the production of various aliphatic and aromatic hydrocarbons by the fungi could play an important role in the deterioration process.