Biology subjects

Martineau, C.

Publications and source records attributed to Martineau, C..

8 recordsLinked to original sources

bioRxiv2026

Synergistic plant-microbe interactions drive the remediation of naphthenic acid fractional compounds in a constructed wetland mesocosm

Constructed wetland treatment systems (CWTSs) are promising options for treating oil-sands process-affected water (OSPW), which contains toxic naphthenic acid fraction compounds (NAFCs). However, the molecular mechanisms underlying NAFCs attenuation by plants and root microbes remain poorly resolved. In our previous mesocosm study, common cattail (Typha latifolia) increased NAFCs removal by 2.5-fold relative to unplanted controls with no significant effect on plant growth. Here, using RNA from the same experimental system, we applied metatranscriptomics to 40 root samples collected over 60 days to examine plant and active-microbial responses to OSPW exposure. The active-root-associated-microbial community was dominated by Pseudomonadota, which showed a slight increase with exposure to OSPW. Burkholderiales were the most active family, though their relative activity decreased in OSPW systems, where Flavobacteriaceae (Bacteroidota) activity increased. Clear microbial-community shifts were driven by time and OSPW exposure. Although 18 previously proposed microbial NAFC-degradation genes were not differentially expressed, 42 other genes with potential roles in NAFC or related organic compound degradation showed differential expression in OSPW-filled mesocosms. This activity was dominated by specific oxidoreductases from Burkholderiales and Rhizobiales. Crucially, host plant actively responded to OSPW, robustly up-regulating genes encoding oxidoreductases, transporters, and glycosyltransferases, some of which are related to xenobiotic stress and detoxification. Taken together, these results show coordinated plant and microbial transcriptional responses in a system where NAFC removal had already been measured chemically. They help explain the response of OSPW-exposed mesocosms, but the observed patterns likely reflect the broader OSPW mixture rather than NAFCs alone.

ecology↗

bioRxiv2025

Lake floodplains as sinks for stable soil organic carbon: is the carbon plant- or microbe-derived, and why does permanent land use matter?

Floodplain ecosystems play a key role in soil organic carbon (SOC) storage, as they integrate inputs from both vegetation and sediments. Promoting land uses with low anthropogenic disturbances helps maintain the function of these ecosystems as soil carbon (C) sinks. However, the tipping points along a disturbance gradient where land use transitions generate the largest SOC losses or gains remain unclear, though they are key for effective land use management and climate change mitigation. Because flood events can negatively impact labile C, determining the main origin of stable SOC, whether from plants or soil microorganisms, is also important to identify the optimal combination of land use, vegetation, and soil type for SOC stabilization in floodplains. We examined how SOC storage and stabilization vary in the floodplain of Lake Saint-Pierre, Quebec, Canada along an anthropogenic disturbance gradient of six land uses: conventional and improved croplands, temporary and permanent meadows, marshes, and forested swamps. In all 6 land uses, we quantified SOC stocks, mineral-associated organic matter - C (MAOM-C), particulate organic matter - C (POM-C), soil {delta}13C and sugars. Land use effects on SOC storage and stabilization were most pronounced in the topsoil (0-10 cm), with forested swamps showing the highest vegetation biomass, SOC, and MAOM-C. Microbe-derived inputs were more abundant in MAOM, whereas plant-derived C dominated POM. SOC gains increased with decreasing disturbance, with a tipping point occurring in the transition from temporary to permanent meadows. Our results highlight the importance of conserving permanent and low-disturbance land uses to promote SOC persistence in floodplain ecosystems and emphasize the central role of microbial metabolism in stabilization processes.

ecology↗

bioRxiv2025

Soil microbiomes reveal different strategies for nitrogen acquisition in aspen-dominated stands from Mexico and Canada

Plant species shape soil microbiome composition through species-specific interactions. However, it is less clear how these interactions vary across populations that diverged a long time ago. In this study, we explore the influence of host genetic composition and edaphic factors on the soil microbiome of Populus tremuloides, one of North Americas most widespread tree species. Using 16S, 18S rRNA gene, and ITS2 region metabarcoding on soils from natural stands and potting mix, rhizosphere, and root samples from a greenhouse common garden, we examined prokaryotic and fungal communities in two aspen genetic groups. The Eastern Canada group represents boreal and cold temperate ecoregions, and the one from Northwestern Mexico represents warm temperate ecoregion. Variation in microbial community structure correlated with soil properties but results from common gardens indicated that the host genetic makeup may also play a role. The three ecoregions showed functional divergence: warm temperate sites hosted a higher abundance and diversity of nitrogen-fixing bacteria, while boreal stands exhibited stronger associations with ectomycorrhizal fungi. Our findings highlight how local adaptations to climate and soil conditions in aspen extend to their microbial partners, emphasizing the potential role of host-microbe interactions in shaping tree resilience and susceptibility to future climate changes.

evolutionary biology↗

bioRxiv2022

Universal microbial reworking of dissolved organic matter along environmental gradients

Soils are losing increasing amounts of carbon annually to freshwaters as dissolved organic matter (DOM), which, if degraded, can accelerate climate change. DOM is more susceptible to degradation closer to its source and becomes increasingly dominated by the same, difficult-to-degrade compounds as degradation proceeds. However, the processes underlying DOM degradation across environments are poorly understood. Here we found DOM changed similarly along soil-aquatic gradients irrespective of differences in environmental conditions. Using ultra-high-resolution mass spectrometry, we tracked DOM along soil depths and hillslope positions in forest headwater catchments and related its composition to soil microbiomes and physical chemistry. Along depths and hillslopes, carbohydrate-like and unsaturated hydrocarbon-like compounds increased in mass, suggestive of microbial reworking of plant material. More than half of the variation in the abundance of these compounds was related to the expression of genes essential for degrading plant-derived carbohydrates. Our results implicate continuous microbial reworking in shifting DOM towards universal compounds in soils. By synthesising data from the land-to-ocean continuum, we suggest these processes can generalise across ecosystems and spatiotemporal scales. Such general degradation patterns can be leveraged to predict DOM composition and its downstream reactivity along environmental gradients to inform management of soil-to-stream carbon losses.

ecology↗

bioRxiv2021

The biological sink of atmospheric H2 is more sensitive to spatial variation of microbial diversity than N2O and CO2 emissions in an agroecosystem

The relationship between soil microbial diversity and agroecosystem functioning is controversial due to the elevated diversity level and the functional redundancy of microorganisms. A field trial was established to test the hypothesis that enhanced crop diversity with the integration of winter cover crops (WCC) in a conventional maize-soy rotation promotes microbial diversity and the biological sink of H2 in soil, while reducing N2O emissions to the atmosphere. Vicia villosa (hairy vetch), Avena sativa (oat), and Raphanus sativus (Daikon radish) were cultivated alone or in combinations and flux measurements were performed throughout two subsequent growing seasons. Soil acted as a net sink for H2 and as a net source for CO2 and N2O. CO2 flux was the most sensitive to WCC whereas a significant spatial variation was observed for H2 flux with soil uptake rates observed in the most productive area two-fold greater than the baseline level. Sequencing and quantification of taxonomic and functional genes were integrated to explain variation in trace gas fluxes with compositional changes in soil microbial communities. Fungal communities were the most sensitive to WCC, but neither community abundance nor beta diversity were found to be indicative of fluxes. The alpha diversity of taxonomic and functional genes, expressed as the number of effective species, was integrated into composite variables extracted from multivariate analyses. Only the composite variable computed with the inverse Simpsons concentration index displayed a reproducible pattern throughout both growing seasons, with functional genes and bacterial 16S rRNA gene defining the two most contrasting gradients. The composite variable was decoupled from WCC treatment and explained 19-20% spatial variation of H2 fluxes. Sensitivity of the trace gas exchange process to soil properties at the local scale was inconsistent among H2, N2O and CO2, with the former being the most related to microbial diversity distribution pattern.

ecology↗

bioRxiv2020

Plant Genotype Influences Physicochemical Properties of Substrate as well as Bacterial and Fungal Assemblages in the Rhizosphere of Balsam Poplar

Abandoned unrestored mines are an important environmental issue since they typically remain unvegetated for decades, exposing vast amounts of mine waste to erosion. Several factors limit the revegetation of these sites, including extreme abiotic conditions and unfavorable biotic conditions. However, some pioneer tree species having high level of genetic diversity, such as balsam poplar (Populus balsamifera), are able to naturally colonize these sites and initiate plant succession. This suggests that some tree genotypes are likely more suited for acclimation to the conditions of mine wastes. In this study, two contrasting mine waste storage facilities (waste rock versus tailings) from the Abitibi region of Quebec (Canada), on which poplars have grown naturally, were selected. First, we assessed in situ the impact of vegetation presence on each type of mine wastes. The presence of balsam poplars improved soil health locally by improving physicochemical properties (e.g. higher nutrient content and pH) of the mine wastes and causing an important shift in their bacterial and fungal community compositions, going from lithotrophic communities that dominate mine waste environments to heterotrophic communities involved in nutrient cycling. Next, in a greenhouse experiment, ten genotypes of P. balsamifera collected on both mine sites and from a natural forest nearby were grown in these mine wastes. Tree growth was monitored during two growing seasons, after which the effect of genotype-by-environment interactions was assessed by measuring the physicochemical properties of the substrates and the changes in microbial communities, using a metabarcoding approach. Although substrate type was identified as the main driver of rhizosphere microbiome diversity and community structure, a significant effect of tree genotype was also detected, particularly for bacterial communities. Plant genotype also influenced aboveground tree growth and the physicochemical properties of the substrates. These results highlight the influence of balsam poplar genotype on the soil environment and the potential importance of tree genotype selection in the context of mine waste revegetation.

ecology↗

bioRxiv2019

Impact of NaCl, nitrate and temperature on the microbial community of a methanol-fed, denitrifying marine biofilm

BackgroundThe biofilm of a continuous, methanol-fed, fluidized denitrification system that treated a marine effluent at the Montreal Biodome is composed of a multi-species microbial community, among which Hyphomicrobium nitrativorans NL23 and Methylophaga nitratireducenticrescens JAM1 are the principal bacteria involved in the denitrifying activities. To assess its resilience to environmental changes, the biofilm taken from the denitrification system was cultured at laboratory scale in artificial seawater (ASW) under anoxic conditions and exposed to a range of specific physico-chemical parameters. We previously showed that the seawater formulation and the NaCl concentrations had a strong impact on the H. nitrativorans NL23 population, with its displacement by a new denitrifier, M. nitratireducenticrescens GP59. Here, we report the impact of these cultures conditions on the dynamics of the overall microbial community of the denitrifying biofilm.\n\nMethodsThe original biofilm (OB) taken from the denitrification system was acclimated for five weeks in ASW under anoxic conditions with a range of NaCl concentrations, and with four combinations of nitrate concentrations and temperatures. The OB was also acclimated to the commercial Instant Ocean seawater medium (IO). The bacterial diversity of the biofilm cultures and the OB was determined by 16S ribosomal RNA amplicon metagenome sequencing. Culture-dependent approach was used to isolate other denitrifying bacteria from the biofilm cultures. The metatranscriptomes of some of the biofilm cultures were derived, along with the transcriptomes of planktonic pure cultures of H. nitrativorans NL23 and M. nitratireducentricrescens GP59 cultivated under denitrifying conditions.\n\nResultsThe 16S metagenomic data revealed very high proportions of M. nitratireducenticrescens in the biofilm cultures. H. nitrativorans NL23 was found in high proportion in the OB, both was absent in the biofilm cultures with 2.75% NaCl in the ASW medium. It was found however in low proportions in the biofilm cultures with 0 to 1% NaCl in the ASW medium and in the IO biofilm cultures. Emergence of Marinicella spp. occurred in these biofilm cultures. Denitrifying bacterial isolates affiliated to Marinobacter spp. and Paracoccus spp. were isolated. Up regulation of the denitrification genes in strains GP59 and NL23 occurred in the biofilm cultures compared to the planktonic pure cultures. Denitrifying bacteria affiliated to the Stappia spp. were metabolically active in the biofilm cultures.\n\nConclusionsThese results illustrate the dynamics of the microbial community in the denitrifying biofilm cultures in adapting to different environmental conditions. The NaCl concentration is an important factor affecting the microbial community in the biofilm cultures. Up regulation of the denitrification genes in strain GP59 and strain NL23 in the biofilm cultures suggests different mechanisms of regulation of the denitrification pathway in the biofilm compared to the planktonic pure cultures. Other denitrifying heterotrophic bacteria are present in low proportions in the biofilm, suggesting that the biofilm has the potential to adapt to heterotrophic, non-methylotrophic environments.

microbiology↗

bioRxiv2019

Impact of physico-chemical parameters on the denitrification and the co-occurrence of Methylophaga nitratireducenticrescens and Hyphomicrobium nitrativorans in a methanol-fed marine denitrifying biofilm

BackgroundThe biofilm of a continuous, methanol-fed, fluidized denitrification system that treated a marine effluent is composed of multi-species microorganisms, among which Hyphomicrobium nitrativorans NL23 and Methylophaga nitratireducenticrescens JAM1 are the principal bacteria involved in the denitrifying activities. This biofilm can be cultured at laboratory-scale under batch mode conditions without losing the denitrifying activities. Here, we report the capacity of the denitrifying biofilm to sustain changes to specific physico-chemical parameters, and the impact of these changes on the denitrification performance and the co-occurrence of H. nitrativorans and M. nitratireducenticrescens.\n\nMethodsThe original biofilm (OB) taken from the denitrification system was acclimated to an artificial seawater (ASW) medium under anoxic conditions to generate the Reference biofilm cultures (300 mg-NO3--N/L, 23{degrees}C). In the first set of assays, the Reference biofilm cultures were subjected to short exposures (1-3 days) of a range of NaCl, methanol, nitrate (NO3-) and nitrite (NO2-) concentrations, and to different pHs and temperatures. In the second set of assays, the OB was acclimated in an ASW-modified medium for five weeks i) to a range of NaCl concentrations (0% to 8%), ii) to four combinations of NO3- concentrations and temperatures, iii) to NO2-, and iv) under oxic conditions. Finally, the OB was acclimated to the commercial Instant Ocean (IO) medium. The growth of the biofilm and the dynamics of NO3- and NO2- were determined. The levels of M. nitratireducenticrescens and H. nitrativorans were measured by qPCR in these cultures.\n\nResultsThe denitrifying capacities of the OB was preserved in the Reference biofilm cultures. In these cultures, however, H. nitrativorans NL23 decreased by three orders of magnitude in concentration with the occurrence of the same magnitude of a new denitrifying bacterial strain (M. nitratireducenticrescens GP59). Results from the first set of assays showed that the Reference biofilm cultures can sustain denitrifying activities in most of the tested conditions. Inhibition occurred when these biofilm cultures were exposed at pH 10 or with 1.5% methanol. Results from the second set of assays showed the persistence of H. nitrativorans NL23 in the biofilm cultures acclimated to low NaCl concentrations (0% to 1.0%). Poor biofilm development occurred in biofilm cultures acclimated to 5% and 8% NaCl. Finally, high proportion of H. nitrativorans NL23 was found in the IO biofilm cultures.\n\nConclusionsThese results confirm the plasticity of the marine methylotrophic denitrifying biofilm in adapting to different conditions. The NaCl concentration is a crucial factor in the dynamics of H. nitrativorans NL23, for which growth was impaired above 1% NaCl in the ASW-based biofilm cultures in favor of M. nitratireducenticrescens GP59. This study contributes to the understanding on the population dynamics of co-occurring bacteria performing denitrifying activities in biofilm under seawater environment. This could benefit in the development of optimal denitrifying bioprocess under marine conditions.

microbiology↗