New insights into the habitat shifts of odor-producing terrestrial cyanobacteria into water systems based on Nostoc (Nostocales, Cyanobacteria), the first reported 2-methylisoborneol producer

Abstract

Numerous microorganisms, including cyanobacteria, actinomycetes, myxobacteria, and fungi, produce compounds with earthy and musty odors. The odor-producing cyanobacteria have been studied and limited to freshwater environments with Nostoc, particularly known as a geosmin-producing species; as no strains producing 2-MIB have yet to be reported. In this study, we discovered, for the first time, that Nostoc sp. HNIBRCY4 produces 2-MIB compounds in the soil, suggesting that these cyanobacteria, along with their odorous byproducts, could be washed into freshwater sources from the soil during rainfall, which could cause occasional odor problems in freshwater. NGS analysis revealed that soil cyanobacteria spread from the side of the stream to the center by rainfall. Furthermore, we investigated the effect of the conditions of nutrients on the production of 2-MIB by Nostoc sp. HNIBRCY4, setting up four different trophic groups of nutrients (autotrophic, diazotrophic, heterotrophic, and mixotrophic conditions). This set of groups provides a fundamental understanding of how terrestrial cyanobacteria change their growth and metabolism in different environments and whether they are flexible enough to adapt to environmental changes from terrestrial to aquatic systems. The results indicated that 2-MIB production increased significantly under autotrophic conditions (62.1？68.9？μg/g) compared to mixotrophic conditions (24.4？25.3？μg/g). This is the first case study to describe the terrestrial cyanobacterium Nostoc sp. HNIBRCY4 produces 2-MIB, suggesting that cyanobacteria in the soil can not only survive after being washed into water bodies during rain, but can also produce 2-MIB at 2-fold higher levels.