Biology subjects

Lirette, A.-O.

Publications and source records attributed to Lirette, A.-O..

3 recordsLinked to original sources

bioRxiv2026

Long-term patterns of ultra-low sulfur fuel oil bioremediation in Arctic shorelines using in situ mesocosms

New maritime regulations restricting high-sulfur fuels have led to the transition to new low sulfur fuel oils (LFSOs). We do not know how LSFOs will behave in marine environments and how they will respond to available remediation strategies, presenting an environmental risk. The risk will be even higher in the remote high Arctic, especially along the Northwest Passage (NWP), for which an increase in shipping traffic is expected by the end of the century. In this study, we evaluated the long-term (one year) biodegradation potential of the native microbial community of NWP beach sediment using in situ mesocosm experiments with two different types of LSFOs: a marine gas oil (Marine diesel) and an ultra-low sulfur fuel oil (ULSFO). We observed that the lighter Marine diesel was biodegraded better (72.0%) than the heavier ULSFO (32.5%). We described composition of the microbial community of the mesocosms using 16S rRNA gene amplicon sequencing and observed a decrease in microbial diversity for the fuel-treated samples compared to the untreated controls. Despite the decrease in overall diversity, we observed significantly higher abundances of known hydrocarbon degrading microbes (e.g., Oleispira, Altererythrobacter, Gilvibacter, Pseudohongiella) in the fuel mesocosms. Our study showed the potential to implement biodegradation as a remediation strategy under the cold and oligotrophic environmental conditions present throughout the NWP. However, we also observed that microbes on their own cannot degrade the entirety of the removed fuel and other types of remediation will need to be considered to complement the natural biodegradation observed here.

microbiology↗

bioRxiv2025

From Northwest Passage shores to molecular pathways: Comparative transcriptomic responses of a novel Arctic marine fuel-degrading Flavobacterium species

Accelerated sea-ice decline is opening the Arctic to increased shipping, elevating the risk of marine fuel spills in fragile ecosystems where extreme cold and remoteness limit cleanup options. While microbial biodegradation is the primary removal mechanism, the metabolic strategies of abundant polar taxa remain poorly understood, particularly those lacking canonical degradation genes. We characterized the hydrocarbon degradation mechanisms of Flavobacterium sp. strain R2B_3I, a psychrotolerant isolate from high Arctic beach sediments in Resolute Bay, Nunavut, Canada. During three-month incubations with ultra-low sulfur fuel oil at 4 {degrees}C, R2B_3I mounted a systems-level response involving the upregulation of diverse non-canonical oxidoreductases, membrane remodeling systems, cold-shock, and oxidative stress defenses. Crucially, this strain achieved efficient degradation in the complete absence of alkB alkane hydroxylases, challenging the reliance on alkB as a universal biomarker for hydrocarbon biodegradation. Transcriptomic analysis revealed distinct temporal shifts, linking specific gene clusters to the degradation of complex petroleum mixtures under environmentally relevant conditions. These results demonstrate that Flavobacterium, a dominant genus in polar oceans, utilize a "cryptic" metabolic network to process hydrocarbons, effectively bypassing the pathways typically monitored in environmental surveys. By uncovering alternative mechanisms, our study revises current models of microbial oil degradation, highlighting the overlooked potential of non-canonical degraders in determining the fate of marine fuel spills in a warming Arctic.

microbiology↗

bioRxiv2025

Evolution in spatiotemporal infection patterns of Burkholderia sensu lato lineages in the gut of Riptortus pedestris

Many plants and animals form specific symbioses with microorganisms, relying on bidirectional interactions between hosts and bacteria. However, the knowledge about the evolution of symbiont traits enabling such specificity remains very limited. The bean bug Riptortus pedestris acquires Caballeronia from environmental soil and harbors it in its gut symbiotic organ. This bug-Caballeronia symbiosis is an ideal model to clarify the evolutionary process of symbiotic bacteria because members of their outgroups, such as Paraburkholderia and Pandoraea, can also colonize the host symbiotic organ but are outcompeted when co-inoculated with the native symbiont, Caballeronia. In this study, mechanisms underpinning the competitiveness of Caballeronia inside the insect gut were investigated. First, comparative microscopy revealed that Caballeronias success in the gut is largely attributed to its ability to migrate rapidly to the M4 region through chemotaxis, wherein a cheA insertion mutant showed significantly delayed infection speed and lower competitiveness against wild-type. In addition, Paraburkholderia and Pandoraea frequently formed biofilm-like aggregates in the midgut, which could delay their colonization. By contrast, Caballeronia formed no biofilm-like aggregates, at least inside the insect gut. This study reveals that Caballeronia symbiont has evolved traits like chemotaxis and reaction against AMP to establish an efficient and exclusive symbiotic relationship with their bean bug host. Although the genetic and molecular bases of the chemotaxis and the cell aggregates remain unclear, it is strongly suggested that the dynamic gain and loss of these traits enables Caballeronia to specifically associate with the insect host, R. pedestris. ImportanceRiptortus pedestris, a major soybean pest in East Asia, acquires symbiotic bacteria from the environment every generation, yet its gut is consistently and specifically colonized by Caballeronia species. The evolutionary traits that underlie this strong symbiotic specificity remain poorly understood. Here, we demonstrate that Caballeronia insecticola has acquired two key traits: positive chemotaxis toward the symbiotic organ and tolerance to host-derived antimicrobial peptides (AMPs). Using comparative colonization assays with wild-type, chemotaxis-deficient mutants, a non-symbiotic sister group, and their common ancestor, we show that these adaptations enable Caballeronia to outcompete other bacteria within the host gut. Our findings provide direct evidence that specific ecological and behavioral traits contribute to the establishment of exclusive symbiotic associations, shedding light on how symbiotic specificity can evolve even in horizontally transmitted systems. This work offers novel insights into the evolutionary dynamics of host-microbe interactions.

microbiology↗