Thermal Tolerance Research Articles

Changes in morphological and physiological traits of urban trees in response to elevated temperatures within an Urban Heat Islands.

Urban Heat Islands (UHI) are a common phenomenon in metropolitan areas worldwide where the air temperature is significantly higher in urban areas than in surrounding suburban, rural or natural areas. Mitigation strategies to counteract UHI effects include increasing tree cover and green spaces to reduce heat. The successful application of these approaches necessitates a deep understanding of the thermal tolerances in urban trees and their susceptibility to elevated urban temperatures. We evaluated how the photosynthetic thermal optimum (Topt), photosynthetic heat tolerance (T50), and key leaf thermoregulatory morphological traits (leaf area, specific leaf area, leaf width, thickness and LDMC) differ between conspecific trees growing in 'hot [UHI]' vs. 'cool' parts of Montreal, Canada (with a difference of 3.4°C in air temperature), to assess the ability of seven common tree species to acclimation to higher temperatures. We hypothesized that individuals with hotter growing temperatures would exhibit higher Topt and T50, as well as leaf thermoregulatory morphological traits aligned with conservative strategies (e.g., reduced leaf area and increased leaf mass) compared to their counterparts in the cooler parts of the city. Contrary to our a priori hypotheses, leaf area increased with growing temperatures and only four of the seven species had higher T50 and only three had higher Topt values in the hotter area. These results suggest that many tree species cannot acclimate to elevated temperatures and that the important services they provide, such as carbon capture, can be negatively affected by high temperatures caused by climate change and/or the UHI effect. The ability vs inability of tree species to acclimate to high temperatures should be considered when implementing long term tree planting programs in urban areas.

MaPom1, a Dual-Specificity Tyrosine Phosphorylation-Regulated Kinase, Positively Regulates Thermal and UV-B Tolerance in Metarhizium acridum

Fungi play irreplaceable roles in the functioning of natural ecosystems, but global warming poses a significant threat to them. However, the mechanisms underlying fungal tolerance to thermal and UV-B stresses remain largely unknown. Dual-specificity tyrosine phosphorylation-regulated kinase (DYRK) Pom1 is crucial for fungal growth, conidiation, and virulence. However, its role in stress tolerance within kingdom fungi has not been explored. In this study, we analyzed the function of MaPom1 (a Pom1 homologous gene) in the entomopathogenic fungus Metarhizium acridum and its regulatory roles in stress tolerance. Conidial thermal and UV-B tolerance significantly decreased in the MaPom1 disruption strain (ΔMaPom1), whereas conidial yield and virulence were unaffected. RNA-Seq analysis indicated that the differentially expressed genes (DEGs) were primarily related to amino sugar, nucleotide sugar metabolism, cell wall components, growth and development, and stress response pathways. Under heat shock treatment, the expression levels of heat shock protein genes decreased significantly, leading to reduced thermotolerance. Moreover, under UV-B treatment, MaPom1 expression and the enzyme activity significantly changed, indicating its involvement in regulating UV-B tolerance. The percentage of nuclear damage in ΔMaPom1 under UV-B treatment was higher than that in the wild-type strain (WT) and the complementary strain (CP). Additionally, the transcription levels of DNA damage-related genes significantly decreased, whereas those of several genes involved in the DNA damage repair response increased significantly. Overall, MaPom1 contributed to thermal and UV-B tolerance by regulating the expression of heat shock protein genes and DNA damage repair genes.

Niche Theory and Species Range Limits Along Elevational Gradients: Perspectives and Future Directions

Despite two centuries of research, the mechanisms underlying the formation of species’ elevational range limits remain poorly understood. The climatic variability hypothesis highlights the role of climatic conditions in shaping species’ thermal tolerance and distribution ranges, while the species interactions–abiotic stress hypothesis underscores the relative importance of biotic factors and abiotic stress along environmental gradients. We emphasize Darwin's perspective on the ubiquity of interspecific competition across climatic gradients and the importance of understanding how climate modulates biotic interactions to shape species distributions. Niche theory provides a comprehensive framework, combined with empirical research, to explore how environmental gradients influence species traits, leading to context-dependent species interactions that constrain distributions. In particular, the application of the concept of environmentally weighted performance can further elucidate these complex ecological mechanisms. Future research should integrate multiple approaches, including field and laboratory manipulative experiments, theoretical modeling, and interdisciplinary collaboration, to improve our understanding of species distributions in mountain regions and to inform biodiversity conservation strategies in the face of rapid environmental change.

Research and Application of Thermally Activated Gel for Control of Lost Circulations

Summary Thermally activated gel (TAG) for control of lost circulations was evaluated, which is based on acrylamide (AM) and N-vinylpyrrolidone (NVP) copolymers crosslinked by polyethyleneimine (PEI). Viscoelasticity, pumpable time, breakthrough pressures, thermal tolerance, and fluid compatibility were tested in this paper, and then field applications in Missan Oilfield, Iraq, were introduced. Laboratory results showed that the strain limit in the linear viscoelastic region was 169% and storage modulus was 870 Pa. Pumpable time of TAG varies with pH values, so pumpable time can be controlled above 60 minutes by adjusting pH values in the temperature ranges of 100°C to 140°C. Breakthrough pressures were tested in 5-mm (inner diameter) and 10-mm (inner diameter) simulating pipes.The breakthrough pressure gradients were 1.172 psi/cm and 1.200 psi/cm at 0.5 mL/min and 1.0 mL/min, respectively, for 10-mm simulating pipes, 1.872 psi/cm and 2.200 psi/cm for 5-mm simulating pipes. TAG maintained morphologies completely and dehydrated slightly after 30 days of aging at 140°C, transformed into a degraded and low-viscosity fluid after 45 days of aging. Tests proved that invasions of inorganic electrolytes, drilling fluid additives, and drilling fluids can lengthen the pumpable time of TAG, so flash settings due to invasions could not occur. Applications in Missan Oilfield verified the performances of TAG mentioned above.

Leaf temperatures exceed thermal heat tolerances for a community of eastern North America hardwood trees

Leaf temperatures exceed thermal heat tolerances for a community of eastern North America hardwood trees

Cooling down is as important as warming up for a large-bodied tropical reptile.

An ectotherm's performance and physiological function are strongly tied to environmental temperature, and many ectotherms thermoregulate behaviourally to reach optimum body temperatures. Tropical ectotherms are already living in environments matching their thermal tolerance range and may be expected to conform to environmental temperatures. We tracked the body temperatures (Tb) of 163 estuarine crocodiles across 13 years and compared Tb of 39 crocodiles to water temperature gathered using fish-borne sensors (Tw) across 3 years (2015-2018). While Tb largely conformed closely to Tw, we found inter- and intra-individual differences in relative body temperature (Tb-Tw) that depended on sex and body size as well as the time of day and year. Deviations from Tw, especially during the warm parts of the year, suggest that thermoregulatory behaviour was taking place: we found patterns of warming and cooling events that seemed to mediate this variation in Tb. Thermoregulatory behaviour was observed most frequently in larger individuals, with warming events common during winter and cooling events common during summer. By observing free-ranging animals across multiple years, we found that estuarine crocodiles show yearly patterns of active cooling and warming behaviours that modify their body temperature, highlighting their resilience in the face of recent climate warming. Our work also provides the first evidence for thermal type in large-bodied reptiles.

A tumor Microenvironment-triggered protein-binding Near-infrared-II Theranostic nanoplatform for Mild-Temperature photothermal therapy

Photothermal therapy (PTT) has gained significant attention as a non-invasive treatment in clinical oncology. However, the translation of PTT into clinical practice remains constrained by three fundamental limitations: acquired thermal tolerance in tumor cells, restricted light penetration depth in biological matrices, and insufficient therapeutic outcomes from single-modality treatment. To address these issues, a strategy for forming in situ complexes between near-infrared-II (NIR-II) photothermal agents and proteins is developed, aimed at damaging protein conformation and enhancing PTT effectiveness. We developed a nanoplatform called PCy-SF, consisting of the NIR-II photothermal polymer (PCy) and sorafenib (SF). PCy-SF responds to the tumor microenvironment (TME), specifically releasing Cy-CHO and sorafenib from the assemblies. The released Cy-CHO covalently binds to proteins, forming Cy-Protein complexes that activate NIR-II fluorescence, facilitating NIR-II imaging-guided photothermal therapy. Concurrently, the released SF intensifies microvascular damage, synergizing with PTT for enhanced therapeutic efficacy. Notably, PCy-SF induces a strong anticancer immune response, effectively suppressing tumor recurrence and metastasis. This study introduces a promising protein deactivation strategy for achieving mild-temperature PTT, offering broader applicability of PTT and insights for sensitizing tumors to photothermal therapy. Together, this innovative approach combining NIR-II photothermal agents with protein complexation and a responsive nanoplatform enhances PTT precision and efficacy, demonstrating significant potential in the field of cancer nanomedicine.

Thermoregulation and microhabitat use of Tachymenis peruviana (Dipsadidae) in semi-captivity conditions

Abstract We studied Tachymenis peruviana`s thermoregulatory strategy, and microhabitat use and selection in an open enclosure at 3400 m elevation during the wet season. We expected that thermal conditions at a high elevation locality would result in differences in the thermoregulatory efficiency within microhabitats through their use and selection along the day. We obtained preferred temperatures and critical thermal tolerance limits of field-captured individuals. Some individuals were kept in an open enclosure with access to four microhabitat types with retreats where to hide. We measured individuals’ field-body temperatures along with substrate and air temperatures, and recorded where the snakes were found according to microhabitat type and if they were inside or outside retreats. Meanwhile, operative temperatures were registered every hour at each offered microhabitat between 08:00 to 18:00 hours. The body and microenvironmental temperatures were highly correlated. Even though the enclosure offered appropriate thermal sources for snakes to reach their preferred temperatures, results indicate that the species met its energy requirements with a low effort in this high elevation enclosure. Almost three-quarters of the observations were recorded in retreat sites, showing a lower thermoregulatory efficiency compared to when they were captured aboveground. A comparative evaluation of the thermoregulation of the species in the field within a variety of thermal regimes experienced along its altitudinal and latitudinal range must still be carried out to better understand the species’ thermoregulatory strategies across the Andes.

The predictability of fluctuating environments shapes the thermal tolerance of marine ectotherms and compensates narrow safety margins

Aquatic species living in productive coastal habitats with abundant primary producers have evolved in highly dynamic diel and seasonally fluctuating environments in terms of, for example, water temperature and dissolved oxygen. However, how environmental fluctuations shape the thermal tolerance of marine species is still poorly understood. Here we hypothesize that the degree of predictability of the diel environmental fluctuations in the coastal area can explain the thermal response of marine species. To test this hypothesis, we measured the thermal tolerance of 17 species of marine ectotherm from tropical, warm temperate and cold temperate latitudes under two levels of oxygen (around saturation and at supersaturation), and relate the results to their site-specific temperature and oxygen fluctuation and their environmental predictability. We demonstrate that oxygen and temperature fluctuations at tropical latitudes have a higher predictability than those at warm and cold temperate latitudes. Further, we show that marine species that are adapted to high predictability have the potential to tune their thermal performance when exposed to oxygen supersaturation, despite being constrained within a narrow safety margin. We advocate that the predictability of the environmental fluctuation needs to be considered when measuring and forecasting the response of marine animals to global warming.

Integrated Genomic Approaches to Characterize and Mitigate Heat Stress in Poultry.

With the burgeoning human population, climate change, and expansion of poultry production in hot climates, it is imperative to aid global food security by enhancing the resilience of thermally challenged poultry. As a complement to management approaches used to mitigate heat stress, we give selected examples of recent studies on heat stress in poultry using various omics technologies. An integrated analysis of positional and functional candidate genes is provided, highlighting the most prominent pathways involved in the heat stress response. We finish by discussing efficient strategies to enhance thermal tolerance of poultry by genomics approaches, advocating for preservation of biodiversity that may provide beneficial allelic variation, and identifying current and future challenges in producing climate-resilient poultry.

In thermotolerance tests of tropical tree leaves, the chlorophyll fluorescence parameter Fv/Fm measured soon after heat exposure is not a reliable predictor of tissue necrosis.

Tropical rainforests are hot and may be particularly sensitive to ongoing anthropogenic global warming. This has led to increased interest in the thermotolerance of tropical trees. Thermotolerance of leaves of two tropical tree species, Terminalia catappa and Coccoloba uvifera, was determined by exposing leaf samples to 15-min heat treatments, followed by measurements of potential photosystem II quantum yield (dark-adapted value of variable/maximum chlorophyll a fluorescence, Fv/Fm) after 24 h and 14 days, and visible damage (necrosis) after 14 days. T50 (24 h), the temperature at which Fv/Fm declined by 50% 24 h after heat treatments, was associated with only ~10% leaf area damage in C. uvifera and no damage in T. catappa. In neither species was leaf necrosis observed at T5 (24 h), the temperature at which Fv/Fm declined by 5%. In both species, temperatures significantly higher than T50 (24 h) were required for 50% leaf area necrosis to occur. T50 (14 days) was a better proxy of visible leaf damage than T50 (24 h). The relationship between heat-induced Fv/Fm decline and tissue necrosis varies among species. In species surveys of leaf thermal tolerances, calibration of the Fv/Fm assay against the necrosis test is recommended for each species under investigation. Fv/Fm measurements soon after heat exposure do not reliably predict irreversible heat damage and may thus not be suitable to model and predict the thermostability of tropical forest trees.

Ex situ spawning, larval development, and settlement in massive reef‐building corals (Porites) in Palau

AbstractReproduction, embryological development, and settlement of corals are critical for survival of coral reefs through larval propagation. Yet, for many species of corals, a basic understanding of the early life‐history stages is lacking. In this study, we report our observations for ex situ reproduction in the massive reef‐building coral Porites cf. P. lobata across 2 years. Spawning occurred in April and May, on the first day after the full moon with at least 2 h of darkness between sunset and moonrise, on a rising tide. Only a small proportion of corals observed had mature gametes or spawned (14–35%). Eggs were 185–311 μm in diameter, spherical, homogenous, and provisioned with 95–155 algal cells (family Symbiodiniaceae). Males spawned before females, and ex situ fertilization rates were high for the first 2 h after egg release. Larvae were elliptical, ~300 μm long, and symbiotic. Just 2 days after fertilization, many larvae swam near the bottom of culture dishes and were competent to settle. Settlers began calcification 2 days after metamorphosis, and tentacles were developed 10 days after attachment. Our observations contrast with previous studies by suggesting an abbreviated pelagic larval period in Porites cf. P. lobata, which could lead to the isolation of some populations. The high thermal tolerance and broad geographic range of Porites cf. P. lobata suggest that this species could locally adapt to a wide range of environmental conditions, especially if larvae are locally retained. The results of this study can inform future work on reproduction, larval biology, dispersal, and recruitment in Porites cf. P. lobata, which could have an ecological advantage over less resilient coral species under future climate change.

Physiological and morphological traits affect contemporary range expansion and implications for species distribution modelling in an amphibian species.

Species range shifts due to climate alterations have been increasingly well-documented. Although amphibians are one of the most sensitive groups of animals to environmental perturbations due to climate change, almost no studies have offered evidence of poleward distribution shifts in this taxon in response to climate warming. Range shifts would be facilitated by variation in traits associated with the ability of species to persist and/or shift their range in the face of climate change, but the extent and consequences of intraspecific variation in these traits is unclear. We studied the role of intraspecific variation in the ongoing range shift of green treefrogs (Hyla cinerea) in response to climate change. We explored factors that are often associated with range shifts to test the hypothesis that there are differences in these traits between recently range-expanded and nearby historical populations. We then tested the consequences of intraspecific variation for modelling climate-induced range shifts by comparing species distribution models (SDMs) that used as input either data from the entire species range or separate inputs from 'subpopulations' corresponding to the historical range or the recently expanded range. We expected that building a separate SDM for each population would more accurately characterize the species range if historical and expanded populations differed in traits related to their response to climate. We found that critical thermal minimum decreased and thermal breadth increased with latitude, but the effect of latitude was significantly stronger for expanded populations compared to historical populations. Additionally, we found that individuals from expanded populations had longer leg lengths when compared to their historical counterparts. Finally, we found higher model accuracy for one of the population-level SDMs than the species-level SDM. Our results suggest that thermal tolerance and dispersal morphologies are associated with amphibian distributional shifts as these characteristics appear to facilitate rapid range expansion of a native anuran. Additionally, our modelling results emphasize that SDM accuracy could be improved by dividing a species range to consider potential differences in traits associated with climate responses. Future research should identify the mechanisms underlying intraspecific variation along climate gradients to continue improving SDM prediction of range shifts under climate change.

The evolution of thermal performance curves in fungi farmed by attine ant mutualists in aboveground or belowground microclimates.

Fungi are abundant and ecologically important at a global scale, but little is known about whether their thermal adaptations are shaped by biochemical constraints (i.e. the Hotter is Better Model, HBM) or evolutionary tradeoffs (i.e., the Specialist Generalist Model, SGM). We tested these hypotheses by generating thermal performance curves (TPCs) of fungal cultivars farmed by six species of Panamanian fungus-farming 'attine' ants. These fungi represent evolutionary transitions in farming strategies as four cultivars are farmed by ants belowground at stable temperatures near 25°C and two cultivars are farmed aboveground at variable temperatures. We generated TPCs using a common garden experiment confining fungal isolates to different temperatures and then used a Bayesian hierarchical modeling approach to compare competing temperature sensitivity models. Some thermal performance traits differed consistently across farming strategies, with aboveground cultivars having: 1) higher tolerance to low temperatures (CTLmin) and 2) higher maximum growth rate at the optimal temperature (rmax). However, two core assumptions shared by the HBM or SGM were not supported as aboveground cultivars did not show systematic increases in either their optimal temperature (Topt) or thermal tolerance breadth. These results harness ant farming systems as long-term natural experiments to decouple the effects of environmental thermal variation and innate physiological temperature sensitivity on fungal thermal evolution. The results have clear implications for predicting climate warming induced breaking points in animal-microbe mutualisms.

Sustainable seaweed aquaculture and climate change in the North Atlantic: challenges and opportunities

Seaweed aquaculture is gaining traction globally as a solution to many climate issues. However, seaweeds themselves are also under threat of anthropogenically driven climate change. Here, we summarize climate-related challenges to the seaweed aquaculture industry, with a focus on the developing trade in the North Atlantic. Specifically, we summarize three main challenges: i) abiotic change; ii) extreme events; and iii) disease & herbivory. Abiotic change includes negative effects of ocean warming and acidification, as well as altered seasonality due to ocean warming. This can lower biomass yield and change biochemical composition of the seaweeds. Extreme events can cause considerable damage and loss to seaweed farms, particularly due to marine heatwaves, storms and freshwater inputs. Seaweed diseases have a higher chance of proliferating under environmentally stressful conditions such as ocean warming and decreased salinity. Herbivory causes loss of biomass but is not well researched in relation to seaweed aquaculture in the North Atlantic. Despite challenges, opportunities exist to improve resilience to climate change, summarized in three sections: i) future proof site selection; ii) advances in breeding and microbiome manipulation; and iii) restorative aquaculture. We present a case study where we use predictive modelling to illustrate suitable habitat for seaweed cultivation in the North Atlantic under future ocean warming. Notably, there was a large loss of suitable habitat for cultivating Alaria esculenta and Laminaria digitata. We show how selection and priming and microbe inoculates may be a cost-effective and scalable solution to improve disease- and thermal tolerance. Co-cultivation of seaweeds may increase both yield and biodiversity co-benefits. Finally, we show that aquaculture and restoration can benefit from collaborating on nursery techniques and push for improved legislation.

Thermal Tolerance and Species Distributions: Interactions Between Latitude, Elevation and Arboreality in Ants

ABSTRACTAimGlobal warming has highlighted the importance of understanding the role of thermal tolerance as a driver of species distributions, especially for ectotherms. Here we analyse interactions between latitude, elevation and arboreality as predictors of geographic patterns of thermal tolerance in ants.LocationThe collected data are distributed globally.MethodsWe first tested the effect of latitude, elevation and its interactive effect on ant CTmax and CTmin. Second, we tested whether CTmax and CTmin are phylogenetic clustering. Finally, we tested whether CTmax and CTmin can be explained by nesting microhabitat (ground vs. tree‐nesting species) and whether the probability of occurrence of tree‐nesting species along thermal gradients helps explain the global pattern in ant CTmax.ResultsCTmax and CTmin displayed high and low phylogenetic signals respectively and therefore showed different responses to geographic gradients. Notably, we found that CTmax was higher in higher latitudes. This was explained by a lack of elevational turnover at high latitudes among tree‐nesting species, which are exposed to warmer microclimates and have higher CTmax compared with ground‐nesting species. CTmin decreased with elevation at low latitudes, but did not vary with elevation at higher latitudes.Main ConclusionsOur findings highlight the important influence of arboreality on the macroecology of thermal tolerance, substantially modifying traditional notions of variation along latitudinal and elevation gradients.

High phenotypic diversity correlated with genomic variation across the European Batrachochytrium salamandrivorans epizootic.

Recognizing the influence of pathogen diversity on infection dynamics is crucial for mitigating emerging infectious diseases. Characterising such diversity is often complex, for instance when multiple pathogen variants exist that interact differently with the environment and host. Here, we explore genotypic and phenotypic variation of Batrachochytrium salamandrivorans (Bsal), an emerging fungal pathogen that is driving declines among an increasing number of European amphibian species. For thirteen isolates, spanning most of the known temporal and geographical Bsal range in Europe, we mapped phenotypic diversity through numerous measurements that describe varying reproductive rates in vitro across a range of temperatures. Bsal isolates are revealed to have different thermal optima and tolerances, with phenotypic variation correlating with genomic diversity. Using a mechanistic niche model of the fire salamander (Salamandra salamandra) as an example, we illustrate how host steady-state body temperature and Bsal thermal range variation may influence pathogen growth through space and time across Europe. Our combined findings show how the identity of emergent pathogen variants may strongly influence when and which host populations are most at risk.

ECR Spotlight – Matthew Gilbert

ECR Spotlight is a series of interviews with early-career authors from a selection of papers published in Journal of Experimental Biology and aims to promote not only the diversity of early-career researchers (ECRs) working in experimental biology but also the huge variety of animals and physiological systems that are essential for the ‘comparative’ approach. Matthew Gilbert is an author on ‘ Measuring maximum heart rate to study cardiac thermal performance and heat tolerance in fishes’, published in JEB. Matthew is an Assistant Professor of Animal Physiology at the Institute of Arctic Biology, University of Alaska Fairbanks, USA, investigating environmental drivers of cardiorespiratory and energetic plasticity, thermal physiology and exercise physiology.

Coronary circulation enhances the aerobic performance of wild Pacific salmon.

Female Pacific salmon often experience higher mortality than males during their once-in-a-lifetime up-river spawning migration, particularly when exposed to secondary stressors (e.g. high temperatures). However, the underlying mechanisms remain unknown. One hypothesis is that female Pacific salmon hearts are more oxygen-limited than those of males and are less able to supply oxygen to the body's tissues during this demanding migration. Notably, female hearts have higher coronary blood flow, which could indicate a greater reliance on this oxygen source. Oxygen limitations can develop from naturally occurring coronary blockages (i.e. coronary arteriosclerosis) found in mature salmon hearts. If female hearts rely more heavily on coronary blood flow but experience similar arteriosclerosis levels as males, they will have disproportionately impaired aerobic performance. To test this hypothesis, we measured resting (RMR) and maximum metabolic rate (MMR), aerobic scope (AS) and acute upper thermal tolerance in coho salmon (Oncorhynchus kisutch) with an intact or artificially blocked coronary oxygen supply. We also assessed venous blood oxygen and chemistry (cortisol, ions and metabolite concentrations) at different time intervals during recovery from exhaustive exercise. We found that coronary blockage impaired MMR, AS and the partial pressure of oxygen in venous blood (PvO2) during exercise recovery but did not differ between sexes. Coronary ligation lowered acute upper thermal tolerance by 1.1°C. Although we did not find evidence of enhanced female reliance on coronary supply, our findings highlight the importance of coronary blood supply for mature wild salmon, where migration success may be linked to cardiac performance, particularly during warm water conditions.

Characterization and genomic analysis of the lytic bacteriophage vB_EclM_HK6 as a potential approach to biocontrol the spread of Enterobacter cloacae contaminating food

BackgroundIncreased prevalence of Enterobacter cloacae within food products underscores food as an underexplored reservoir for antibiotic resistance, thus requiring particular intervention. Bacteriophages have been explored as a promising approach for controlling bacterial growth in different matrices. Moreover, their specific interaction and self-replication, put them apart from traditional methods for controlling bacteria in different matrices.MethodsSixteen Enterobacter cloacae strains were recovered from raw chicken. These strains were used to isolate bacteriophages using enrichment protocol. The broad-spectrum bacteriophage was evaluated in terms of thermal, pH, shearing stress and storge. Moreover, its infection kinetics, in vitro antibacterial activity, cytotoxicity were also assessed. Genomic sequencing was performed to exclude any potential virulence or resistance genes. Finally, the capability of the isolated phages to control bacterial growth in different chicken samples was assessed alone and in combination with sodium nitrite.ResultsThe lytic bacteriophage vB_EclM_HK6 was isolated and showed the broadest spectrum being able to infect 8/16 E. cloacae strains with a lytic activity against its host strain, E. cloacae EC21, as low as MOI of 10–6. The phage displays a latent period of 10 min and burst size of 115 ± 44 and resistance frequency of 5.7 × 10–4 ± 3.0 × 10–4. Stability assessment revealed a thermal tolerance up to 60 ˚C, wide range pH stability (3–10) and the ability to withstand shearing stress up to 250 rpm. HK6 shows no cytotoxicity against oral epithelial cells up to 1012 PFU/ml. Genomic analysis revealed a Strabovirus with total size of 177,845 bp that is free from known resistance and virulence genes. Finally, HK6 pretreatment of raw chicken, chicken nuggets and ready-made cheese salad shows a reduced bacterial count up to 4.6, 2.96 and 2.81 log-units, respectively. Moreover, combing HK6 with sodium nitrite further improved the antibacterial activity in both raw chicken and chicken nuggets without significant enhancement in case of cheese salad.ConclusionEnterobacter bacteriophage vB_EclM_HK6 presents a safe and effective approach for controlling E. cloacae contaminating stored chicken food samples. Moreover, they could be combined with a reduced concentrations of sodium nitrite to improve the killing capacity.