Manuel Porcar, Leila Satari

In this thesis, directed by Manuel Porcar, the microbial diversity of various environments has been studied in the context of Lourens Baas Becking's hypothesis “everything is everywhere, but the environment selects”. Part of the research results have been published in the journals Scientific Reports, International Journal of Systematics and Evolutionary Microbiology and Frontiers in Microbiology. The thesis was defended on July 28, 2022.

The number of microbial taxa that inhabit our planet has been estimated at more than one trillion. For decades, the microbial communities of natural environments have been explored, as well as the adaptation mechanisms of the species that compose them and their potential biotechnological applications. Not only natural but also artificial environments are of interest as sources of microbial diversity, although these environments and their microorganisms have received less attention. In the present doctoral thesis, entitled “Extremophilic microorganisms from natural and artificial environments”, the microbiome of several artificial environments has been studied, especially those with particular selective pressures such as desiccation, ultraviolet radiation, salinity, nutrient deprivation, extreme temperatures, low water activity or pH variations. The results showed that, in addition to the human-associated microbiome, which may constitute a considerable fraction of artificial devices, environmental microbial consortia end up establishing themselves in these environments. Among all these microbial communities, some species are Extremophilous and some can tolerate the extreme conditions of their environment, harboring a variety of survival mechanisms. Others have evolved adaptive mechanisms to cope with harsh environmental conditions. For this research, massive sequencing and microorganism culture analyzes were used to describe the microbial communities associated with different environments. Thus, the succession of the microbial community in the colonization of synthetic products such as discarded chewing gum was studied. Microbial species associated with artificial products such as chewing gum, table salts and manufactured devices, such as the ice machine, have been identified and their potential for biotechnological applications is discussed. Individual microorganisms have also been isolated and characterized, including a new species of the genus Sagittula, previously isolated from an aluminum can at the bottom of the sea.

Lourens Baas Becking's popular principle “everything is everywhere, but the environment selects” has often been used as a starting point to question many investigations into microbial diversity and distribution. In this thesis, the microbial diversity of several artificial environments has been studied considering this hypothesis. The microbial distribution and colonization of these environments is also discussed here, as well as the impact of environmental physicochemical factors on the microbial content of artificial habitats. Although the first microbial community in any environment can be influenced by abiotic factors, the results support Bass Becking's hypothesis about the primary role of selective pressure at the ecological microniche scale as a key factor shaping the microbial worlds that thrive in human-created environments.

Leila's pioneering study of the microbiota of discarded chewing gum received the IgNobel Prize in Ecology in September 2021.

Leila Satari carried out his doctoral research in the Biotechnology and Synthetic Biology group under the supervision of Manuel Porcar, researcher at the University of Valencia at the Institute of Integrative Systems Biology I²SysBio (UV-CSIC). The qualifying panel was made up of Carlos García-Ferris (I²SysBio), Cristina Vilanova (Darwin Bioprospecting Excellence), and Josefa Antón (Universitat d’Alacant), who rated the thesis as outstanding.