New manganese-oxidizing <i>Acremonium</i> -like fungi from halophytic rhizospheres in the Yellow River Delta, China

Abstract

Manganese (Mn) plays a vital role in soil chemistry, plant nutrition, and contaminant cycling, with certain microorganisms capable of transforming soluble Mn(II) into insoluble biogenic manganese oxides. Among these microorganisms, filamentous fungi are especially effective Mn oxidizers, often surpassing bacteria under challenging environmental conditions. The <i>Acremonium</i>-like fungi, historically recognized for their ecological versatility and production of bioactive metabolites, are now known to be highly polyphyletic, with species spanning multiple genera within the family Bionectriaceae. Despite their diversity, the ecological functions of these fungi remain poorly understood, and Mn-oxidizing activity has not previously been reported from this family. In this study, we surveyed saline-alkali soils in Dongying and Binzhou, Shandong Province, China. Seven <i>Acremonium</i>-like fungal isolates from halophytic rhizospheres were recovered from Dongying, but not from Binzhou. Multilocus phylogenetic analyses using ITS (internal transcribed spacer), 28S (28S ribosomal large subunit), <i>tef1-α</i> (elongation factor 1-alpha), and <i>rpb2</i> (second largest subunit of RNA polymerase II), along with detailed morphological characterization, demonstrated that these isolates represent three previously undescribed species within the genera <i>Acremonium, Protocreopsis</i>, and <i>Verruciconidia</i>. Remarkably, all isolates exhibited Mn(II)-oxidizing activity, representing the first report of this trait in Bionectriaceae. These findings broaden the taxonomic and ecological understanding of <i>Acremonium</i>-like fungi and suggest their potential role in manganese cycling in extreme soils. Their tolerance to environmental stress, combined with Mn-oxidizing capabilities, indicates potential applications in bioremediation, soil health enhancement, and biotechnology. By uncovering novel extremophilic fungi with functional significance, this study provides insights into microbial adaptation in harsh environments and identifies promising resources for the sustainable management of saline-alkali soils.