Microbial assemblages associated with extreme Australian environments and their biosynthetic potential

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.