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Background: Synthetic algal-fungal and algal-bacterial cultures have been investigated as a means to enhance the technological applications of the algae. This inclusion of other microbes has enhanced growth and improved stress tolerance of the algal culture. The goal of the current study was to investigate natural microbial consortia to gain an understanding of the occurrence and benefits of these associations in nature. The photosynthetic protist Euglena mutabilis is often found in association with other microbes in acidic environments with high heavy metal (HM) concentrations. This may suggest that microbial interactions are essential for the protist's ability to tolerate these extreme environments. Our study assessed the Cd tolerance of a natural fungal-algal-bacterial (FAB) association whereby the algae is E. mutabilis., Results: This study provides the first assessment of antibiotic and antimycotic agents on an E. mutabilis culture. The results indicate that antibiotic and antimycotic applications significantly decreased the viability of E. mutabilis cells when they were also exposed to Cd. Similar antibiotic treatments of E. gracilis cultures had variable or non-significant impacts on Cd tolerance. E. gracilis also recovered better after pre-treatment with antibiotics and Cd than did E. mutabilis. The recoveries were assessed by heterotrophic growth without antibiotics or Cd. In contrast, both Euglena species displayed increased chlorophyll production upon Cd exposure. PacBio full-length amplicon sequencing and targeted Sanger sequencing identified the microbial species present in the E. mutabilis culture to be the fungus Talaromyces sp. and the bacterium Acidiphilium acidophilum., Conclusion: This study uncovers a possible fungal, algal, and bacterial relationship, what we refer to as a FAB consortium. The members of this consortium interact to enhance the response to Cd exposure. This results in a E. mutabilis culture that has a higher tolerance to Cd than the axenic E. gracilis. The description of this interaction provides a basis for explore the benefits of natural interactions. This will provide knowledge and direction for use when creating or maintaining FAB interactions for biotechnological purposes, including bioremediation., (© 2024. The Author(s).)

Heavy metal (HM) pollution threatens human and ecosystem health. Current methods for remediating water contaminated with HMs are expensive and have limited effect. Therefore, bioremediation is being investigated as an environmentally and economically viable alternative. Freshwater protists Euglena gracilis and Euglena mutabilis were investigated for their tolerance to cadmium (Cd). A greater increase in cell numbers under Cd stress was noted for E. mutabilis but only E. gracilis showed an increase in Cd tolerance following pre-treatment with elevated concentrations of S or N. To gain insight regarding the nature of the increased tolerance RNA-sequencing was carried out on E. gracilis. This revealed transcript level changes among pretreated cells, and additional differences among cells exposed to CdCl 2 . Gene ontology (GO) enrichment analysis reflected changes in S and N metabolism, transmembrane transport, stress response, and physiological processes related to metal binding. Identifying these changes enhances our understanding of how these organisms adapt to HM polluted environments and allows us to target development of future pre-treatments to enhance the use of E. gracilis in bioremediation relating to heavy metals., (© 2024. The Author(s).)

Symbiotic Methylobacterium comprise a significant portion of the phyllospheric microbiome, and are known to benefit host plant growth, development, and confer tolerance to stress factors. The near ubiquitous use of the broad-spectrum herbicide, glyphosate, in farming operations globally has necessitated a more expansive evaluation of the impacts of the agent itself and formulations containing glyphosate on important components of the plant phyllosphere, including Methylobacterium.This study provides an investigation of the sensitivity of 18 strains of Methylobacterium to glyphosate and two commercially available glyphosate-based herbicides (GBH). Nearly all strains of Methylobacterium showed signs of sensitivity to the popular GBH formulations WeatherMax® and Transorb® in a modified Kirby Bauer experiment. However, exposure to pure forms of glyphosate did not show a significant effect on growth for any strain in both the Kirby Bauer test and in liquid broth, until polysorbate-20 (Tween20) was added as a surfactant. Artificially increasing membrane permeability through the introduction of polysorbate-20 caused a 78-84% reduction in bacterial cell biomass relative to controls containing glyphosate or high levels of surfactant only (0-9% and 6-37% reduction respectively). Concentrations of glyphosate as low as 0.05% w/v (500 µg/L) from both commercial formulations tested, inhibited the culturability of Methylobacterium on fresh nutrient-rich medium.To better understand the compatibility of important phyllospheric bacteria with commercial glyphosate-based herbicides, this study endeavours to characterize sensitivity in multiple strains of Methylobacterium, and explore possible mechanisms by which toxicity may be induced., (© 2024. The Author(s).)

Competing Interests: Declaration of Competing Interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: The corresponding author Michael L. Ginger is an Editorial Board member of the journal Protist.