Burtet-Sarramegna, V. | bioRxiv Science

bioRxiv2026

Free-Living Amoeba act as transient permissive hosts for Leptospira spp.

BackgroundLeptospirosis is a zoonotic disease caused by pathogenic Leptospira spp., which persist in soil and water environments for extended periods of time. The mechanisms enabling this environmental survival remain elusive. Free-living amoebae (FLA) are widespread protozoa that act as reservoirs or "Trojan horses" for numerous bacterial pathogens, protecting them from stress and contributing to their persistence. Whether pathogenic Leptospira exploit similar interactions with FLA has not been resolved. Methodology/Principal FindingsUsing live confocal microscopy, flow cytometry, and gentamicin protection assays, we investigated the interactions between pathogenic (Leptospira interrogans) and saprophytic (Leptospira biflexa) leptospires with three FLA species: Acanthamoeba castellanii, Dictyostelium discoideum, and Hartmannella vermiformis. While rapid internalization was observed, entry was only partially dependent on actin-driven processes and was enhanced by the presence of live bacteria. Following internalization, bacteria persisted for at least 48h as indicated by colony-forming assays. However, no evidence of intracellular replication was detected. The number of fluorescently labeled leptospires progressively declined over time, providing further evidence of leptospires survival without multiplication. Finally, analysis of environmental soils in New Caledonia showed co-occurrence of FLA and Leptospira. Soil-derived FLA also internalized pathogenic Leptospira in vitro, showing that these interactions extend to natural isolates. Conclusions/SignificanceOur results demonstrate that free-living amoebae internalize both pathogenic and saprophytic leptospires and allow their transient persistence without replication. By providing protection and prolonging viability in soil environments, FLA may contribute to the ecological maintenance of Leptospira. These findings pinpoint FLA as potential environmental reservoirs that could play a role in shaping leptospires survival strategies relevant for transmission and host infection. Author SummaryFor bacteria living in soils and freshwater environments, survival depends on their ability to adapt to complex ecological landscapes populated by numerous predators and competitors. In such habitats, interactions with other microorganisms are unavoidable and may shape long-term survival strategies. Pathogenic Leptospira, the bacteria responsible for leptospirosis, can persist for long periods outside their hosts, yet the ecological mechanisms supporting this environmental survival remain poorly understood. In soil and freshwater ecosystems, microscopic predators known as free-living amoebae commonly feed on bacteria. However, several bacterial pathogens can survive inside these amoebae and use them as temporary shelters. Because ancestral Leptospira were soil-dwelling saprophytes, interactions with amoebae likely represent an ancient ecological relationship in which successful survival strategies may have evolved and remain conserved in present-day pathogenic species. With this perspective in mind, we used microscopy approaches and bacterial viability assays to investigate whether Leptospira interacts with amoebae. We found that several amoeba species rapidly engulf both pathogenic and non-pathogenic Leptospira. Once internalized, the bacteria remained viable for up to two days but did not multiply. We also detected both amoebae and Leptospira in the same soil samples and showed that environmental amoebae could internalize the bacteria. These findings suggest that amoebae may act as temporary shelters for Leptospira, helping them persist in soils and water and potentially contributing to the environmental stage of leptospirosis transmission.

microbiology↗

bioRxiv2022

Detection of orthologous genes with expression shifts linked to nickel hyperaccumulation across Eudicots

The remarkable capacity of plants to tolerate and accumulate tremendous amount of nickel is a complex adaptative trait that appeared independently in more than 700 species distributed in about fifty families. Nickel hyperaccumulation is thus proposed as a model to investigate the evolution of complex traits in plants. However, the mechanisms involved in nickel hyperaccumulation are still poorly understood in part because comparative transcriptomic analyses struggle to identify genes linked to this trait from a wide diversity of species. In this work, we have implemented a methodology based on the quantification of the expression of orthologous groups and phylogenetic comparative methods to identify genes which expression is correlated to the nickel hyperaccumulation trait. More precisely, we performed de novo transcriptome assembly and reads quantification for each species on its own transcriptome using available RNA-Seq datasets from 15 nickel hyperaccumulator and non-accumulator species. Assembled contigs were associated to orthologous groups built using proteomes predicted from completed plant genome sequences. We then analyzed the transcription profiles of 5953 orthologous groups from distant species using a phylogenetic ANOVA. We identified 31 orthologous groups with an expression shift associated with nickel hyperaccumulation. These orthologous groups correspond to genes that have been previously implicated in nickel accumulation, and to new candidates involved in this trait. We thus believe that this method can be successfully applied to identify genes linked to other complex traits from a wide diversity of species.

plant biology↗

bioRxiv2018

Wide cross-species RNA-Seq comparison reveals a highly conserved role for Ferroportins in nickel hyperaccumulation in plants

The Anthropocene epoch is associated with the spreading of metals in the environment increasing oxidative and genotoxic stress on living organisms1,2. Once regarded as a curiosity, plants hyperaccumulating metals are now envisioned as an opportunity to remediate metal contaminated soils. About 500 plant species adapted to metalliferous soils acquired the capacity to hyperaccumulate (>0.1% of dry weight) nickel in their shoot3. The phylogenetic distribution of these hyperaccumulators in 50 families suggest that this complex trait evolved multiple times independently from basic mechanisms involved in metal homeostasis. However, the exact nature of these mechanisms and whether they are shared between various lineages is not known. Here, using cross-species transcriptomic analyses in different plant families, we have identified convergent functions that may represent major nodes in the evolution of nickel hyperaccumulation. In particular, our data point out that constitutive high expression of IREG/Ferroportin transporters recurrently emerged as a mechanism involved in nickel hyperaccumulation.

plant biology↗