Large-Scale Integration of Amplicon Data Reveals Massive Diversity within Saprospirales, Mostly Originating from Saline Environments

The order <i>Saprospirales</i>, a group of bacteria involved in complex degradation pathways, comprises three officially described families: <i>Saprospiraceae</i>, <i>Lewinellaceae</i>, and <i>Haliscomenobacteraceae</i>. These collectively contain 17 genera and 31 species. The current knowledge on <i>Saprospirales</i> diversity is the product of traditional isolation methods, with the inherited limitations of culture-based approaches. This study utilized the extensive information available in public sequence repositories combined with recent analytical tools to evaluate the global evidence-based diversity of the <i>Saprospirales</i> order. Our analysis resulted in 1183 novel molecular families, 15,033 novel molecular genera, and 188 K novel molecular species. Of those, 7 novel families, 464 novel genera, and 1565 species appeared in abundances at ≥0.1%. <i>Saprospirales</i> were detected in various environments, such as saline water, freshwater, soil, various hosts, wastewater treatment plants, and other bioreactors. Overall, saline water was the environment showing the highest prevalence of <i>Saprospirales</i>, with bioreactors and wastewater treatment plants being the environments where they occurred with the highest abundance. <i>Lewinellaceae</i> was the family containing the majority of the most prevalent species detected, while <i>Saprospiraceae</i> was the family with the majority of the most abundant species found. This analysis should prime researchers to further explore, in a more targeted way, the <i>Saprospirales</i> proportion of microbial dark matter.