Abstract
A wealth of unknown microbial clades and metabolic abilities from physically extreme habitats has been uncovered in recent decades, but the underlying parameters that shape
microbial communities in challenging environments are still poorly understood. The
adaptations of microbes to these stressors are conferred by specialised biosynthetic
pathways to protect against desiccation, osmotic stress and high or low solar irradiation.
These compounds could harbour pharmaceutically active functions but their discovery, characterisation and subsequent production are hindered by the lack of cultivable representative extremophile strains. This study explores mat and microbialite biofilm
communities under extreme conditions that have not been described in depth before. In
addition, their biosynthetic potential is evaluated and the variability within and between
different habitats is explored. Next generation sequencing of the 16S rRNA gene and of two conserved domains of non-ribosomal biosynthetic pathways was performed on
speleothem mat structures of two limestone caves and on mats and microbialites of five
coastal lakes ranging in conductivity from brackish to hypersaline. Environmental parameters were correlated to microbial richness, diversity and distribution to explain
colonisation and succession patterns and to identify the seminal bacterial taxa that drive ecosystem development. Diverse microbial assemblages shaped by pioneer colonisation of
abundant coccoid or filamentous Cyanobacteria are described. Geographical separation
resulted in significantly different microbial communities between locations and environmental parameters shaped successional stages within the mats. High richness and
diversity of biosynthetic pathway domains is discussed in relation to their potential functions in the environment and the dogma that extreme environments prevent chemical
diversity is challenged. This study shows a diversity of prolific natural product producing microbial taxa present in
extreme environments and constitutes an initial screening effort to target microbial habitats for future exploitation of medicinally active compounds.