Biological agents associated with brick biodeterioration in Gonbad-e Qābus tower UNESCO World Heritage site

The World Heritage of Gonbad-e Qābus tower, as one of the architectural masterpieces of the Islamic period of Iran, has been exposed to various biological growths and invasions in the open air. This study aims to identify the type of biological agents living on the ancient brick surfaces in Gonbad-e Qābus tower in Gonbad-e kāvus city in Golestan province. In this research, using field observations, in-site macroscopic observations, microscopic methods, and library studies, biological factors were identified and influenced on the brick surface of the Qaboos dome in three parts: foundation, body, and dome. Based on this, the biodeterioration factors were divided into two sampling groups. The first group includes macro-organisms, which was done to prevent damage based on the identification method based on documentation and camera photography. The second group is the sampling of microorganisms such as bacteria and fungi, microalgae and cyanobacteria, lichens, which are sampled from the brick surface with sterile tweezers and then transferred into the microtube and by the method morphology, culture and microscopy were identified. In general, nine groups of organisms responsible for biodeterioration were identified in this study, among their main groups are bacteria, cyanobacteria and algae, fungi, lichens, mosses and plants, insects and small animals. Macro-organisms increase and decrease with changes in humidity and are therefore effective in the mechanical destruction of substrate components. Among the macro-organisms, plants and mosses were known to be the most important enemies of the existing brick substrate of Gonbad-e Qābus tower. Microorganisms are able to form clones and biofilms on the surface of the brick substrate. They secrete acids that break down the minerals that make up the brick substrate and thus play an important role in the biodeterioration of the building. In general, the bricks of the exterior walls of the building are exposed to the attack of various biological and non-living factors and generally show less resistance to the activities of wear factors. Humidity, temperature and light and urban dust pollution are potential factors in increasing the factors involved in biodeterioration can be discussed in future researches.