Extremely chaotolerant and kosmotolerant Aspergillus atacamensis – a metabolically versatile fungus suitable for recalcitrant biosolid treatment

Obligate halophily is extremely rare in fungi. Nevertheless, Aspergillus atacamensis (strain EXF-6660), isolated from a salt water-exposed cave in the Coastal Range hills of the hyperarid Atacama Desert in Chile, is an obligate halophile, with a broad optimum range from 1.5 to 3.4 M of NaCl. When we tested its ability to grow at varied concentrations of both kosmotropic (NaCl, KCl, and sorbitol) and chaotropic (MgCl2, LiCl, CaCl2, and glycerol) solutes, stereoscopy and laser scanning microscopy revealed the formation of phialides and conidia. A. atacamensis EXF-6660 grew up to saturating levels of NaCl and at 2.0 M concentration of the chaotropic salt MgCl2. Our findings confirmed that A. atacamensis is an obligate halophile that can grow at substantially higher MgCl2 concentrations than 1.26 M, previously considered as the maximum limit supporting prokaryotic life. To assess the fungus’ metabolic versatility, we used the phenotype microarray technology Biolog FF MicroPlates. In the presence of 2.0 M NaCl concentration, strain EXF-6660 metabolism was highly versatile. A vast repertoire of organic molecules (~95% of the substrates present in Biolog FF MicroPlates) was metabolized when supplied as sole carbon sources, including numerous polycyclic aromatic hydrocarbons, benzene derivatives, dyes, and several carbohydrates. Finally, the biotechnological potential of A. atacamensis for xenobiotic degradation and biosolid treatment was investigated. Interestingly, it could remove biphenyls, diphenyl ethers, different pharmaceuticals, phenols, and polyaromatic hydrocarbons. Our combined findings show that A. atacamensis EXF-6660 is a highly chaotolerant, kosmotolerant, and xerotolerant fungus, potentially useful for xenobiotic and biosolid treatments

Horizontal transfer of heavy metal and antibiotic-resistance markers between indigenous bacteria, colonizing mercury contaminated tailing ponds in southern Venezuela, and human pathogens

Abstract: Bacteria colonizing heavily polluted tailing ponds in Southern Venezuela exhibit multiple resistances against mercurial compounds and antibiotics. The corresponding genetic determinants, mainly acquired through horizontal gene transfer, might also be transferred to pathogenic bacteria, an issue which represents an important risk to public health. In this work we show that indigenous, mercury-resistant bacterial strains isolated from a model tailing pond, located in El Callao (Bolivar State, Venezuela) and exhibiting a high concentration of soluble Hg, were able to transfer in vitro both heavy metal- and antibiotic resistance markers to potential human- and animal- pathogens (i.e. Escherichia coli and Pseudomonas aeruginosa). The frequencies of transfer ranged between 1.2x10-6 and 5.5x10-7 transconjugants per recipient. Transconjugants were also detected in the field, in model biofilms previously grown in natural sponges (Luffa cylindrica) and submersed in the ponds, at frequencies ranging from 1x10-4 to 5x10-3 transconjugants per recipient. These results are of particular relevance from the public health viewpoint, especially in light of the potential risk of horizontal flow of antibiotic resistance genes between indigenous bacteria and potential human pathogens.Transferencia horizontal de marcadores de resistencia a metales pesados y antibióticos entre bacterias indígenas, que colonizan lagunas de cola contaminadas con mercurio en el sur de Venezuela, y especies patógenas para el ser humanoResumen: Las bacterias que colonizan lagunas de cola altamente contaminadas en el sur de Venezuela, presentan resistencia a compuestos mercuriales y múltiples antibióticos. Los determinantes genéticos responsables de estas resistencias, adquiridos principalmente a través de transferencia horizontal de genes, pueden ser transferidos a bacterias patógenas. En este trabajo mostramos que cepas bacterianas indígenas, resistentes al mercurio y aisladas a partir de una laguna de cola modelo, localizada en El Callao (Estado Bolívar, Venezuela) conteniendo una alta concentración de Hg soluble, fueron capaces de transferir in vitro marcadores de resistencia a metales y antibióticos a cepas potencialmente patógenas para el hombre y animales (ej. Escherichia coli y Pseudomonas aeruginosa). Las frecuencias de transferencia variaron entre 1,2x10-6 y 5,5x10-7 transconjugantes por receptora. Los transconjugantes también fueron detectados en el campo, utilizando un modelo de biopelículas desarrollado en esponjas naturales (Luffa cylindrica) sumergidas en lagunas contaminadas, con frecuencias que variaron entre 1x10-4 y 5x10-3 transconjugantes por receptora. Estos resultados presentan una relevancia particular desde el punto de vista de salud pública, especialmente en vista del riesgo potencial de transferencia horizontal de genes de resistencia a antibióticos entre las bacterias indígenas y bacterias potencialmente patógenas para el hombre

Fungi beyond limits: The agricultural promise of extremophiles

Abstract Global climate changes threaten food security, necessitating urgent measures to enhance agricultural productivity and expand it into areas less for agronomy. This challenge is crucial in achieving Sustainable Development Goal 2 (Zero Hunger). Plant growth‐promoting microorganisms (PGPM), bacteria and fungi, emerge as a promising solution to mitigate the impact of climate extremes on agriculture. The concept of the plant holobiont, encompassing the plant host and its symbiotic microbiota, underscores the intricate relationships with a diverse microbial community. PGPM, residing in the rhizosphere, phyllosphere, and endosphere, play vital roles in nutrient solubilization, nitrogen fixation, and biocontrol of pathogens. Novel ecological functions, including epigenetic modifications and suppression of virulence genes, extend our understanding of PGPM strategies. The diverse roles of PGPM as biofertilizers, biocontrollers, biomodulators, and more contribute to sustainable agriculture and environmental resilience. Despite fungi's remarkable plant growth‐promoting functions, their potential is often overshadowed compared to bacteria. Arbuscular mycorrhizal fungi (AMF) form a mutualistic symbiosis with many terrestrial plants, enhancing plant nutrition, growth, and stress resistance. Other fungi, including filamentous, yeasts, and polymorphic, from endophytic, to saprophytic, offer unique attributes such as ubiquity, morphology, and endurance in harsh environments, positioning them as exceptional plant growth‐promoting fungi (PGPF). Crops frequently face abiotic stresses like salinity, drought, high UV doses and extreme temperatures. Some extremotolerant fungi, including strains from genera like Trichoderma, Penicillium, Fusarium, and others, have been studied for their beneficial interactions with plants. Presented examples of their capabilities in alleviating salinity, drought, and other stresses underscore their potential applications in agriculture. In this context, extremotolerant and extremophilic fungi populating extreme natural environments are muchless investigated. They represent both new challenges and opportunities. As the global climate evolves, understanding and harnessing the intricate mechanisms of fungal‐plant interactions, especially in extreme environments, is paramount for developing effective and safe plant probiotics and using fungi as biocontrollers against phytopathogens. Thorough assessments, comprehensive methodologies, and a cautious approach are crucial for leveraging the benefits of extremophilic fungi in the changing landscape of global agriculture, ensuring food security in the face of climate challenges