The genus Amphichorda has been recently re-erected as an independent linage from Beauveria, circumscribed within Cordycipitaceae. However, its phylogenetic relationships with other members of this family remain obscure. In our on-going efforts to expand the knowledge on the diversity of culturable ascomycetes from the Mediterranean Sea, we isolated several specimens of Amphichorda. Preliminary sequence analyses revealed great phylogenetic distance with accepted Amphichorda species and a close relation to Onychophora coprophila. Onychophora is a monotypic genus of enteroblastic conidiogenous cells, presumably related to Acremonium (Bionectriaceae); while Amphichorda exhibits holoblastic conidiogenesis. Here, we examine representative strains of Amphichorda species to resolve the taxonomy of the genus and the above-mentioned fungi combining morphological, ultrastructure and multi-locus phylogenetic analyses (ITS, LSU, tef1, BenA). The results revealed Amphichorda as a member of the Bionectriaceae, where its asexual morphs represent a transition between enteroblastic and holoblastic conidiogenesis for this group of fungi. We also describe and illustrate Amphichorda littoralis sp. nov., and propose the new combination Amphichorda coprophila. In addition, we stablish key phenotypic features to distinguish Amphichorda species and demonstrate the higher salt tolerance degree of A. littoralis, consistent with its marine origin. This work provides a comprehensive framework for future studies in the genus.

Whole cell biosensors could serve as eco-friendly and cost-effective alternatives for detecting potentially toxic bioavailable heavy metals in aquatic environments. However, they often fail to meet practical requirements due to an insufficient limit of detection (LOD) and high background noise. In this study, we designed a synthetic genetic circuit specifically tailored for detecting ionic mercury, which we applied to environmental samples collected from artisanal gold mining sites in Peru. We developed two distinct versions of the biosensor, each utilizing a different reporter protein: a fluorescent biosensor (Mer-RFP) and a colorimetric biosensor (Mer-Blue). Mer-RFP enabled real-time monitoring of the culture’s response to mercury samples using a plate reader, whereas Mer-Blue was analysed for colour accumulation at the endpoint using a specially designed, low-cost camera set up for harvested cell pellets. Both biosensors exhibited negligible baseline expression of their respective reporter proteins and responded specifically to HgBr2 in pure water. Mer-RFP demonstrated a linear detection range from 1 nM to 1 μM, whereas Mer-Blue showed a linear range from 2 nM to 125 nM. Our biosensors successfully detected a high concentration of ionic mercury in the reaction bucket where artisanal miners produce a mercury-gold amalgam. However, they did not detect ionic mercury in the water from active mining ponds, indicating a concentration lower than 3.2 nM Hg2+ -a result consistent with chemical analysis quantitation. Furthermore, we discuss the potential of Mer-Blue as a practical and affordable monitoring tool, highlighting its stability, reliance on simple visual colorimetry, and the possibility of sensitivity expansion to organic mercury.