Impacts of Groundwater Pumping on Subterranean Microbial Communities in a Deep Aquifer Associated with an Accretionary Prism.

Accretionary prisms are composed mainly of ancient marine sediment scraped from the subducting oceanic plate at convergent plate boundaries. Anoxic groundwater is stored in deep aquifers associated with accretionary prisms and can be collected via deep wells. We investigated how such groundwater pumping affects the microbial community in a deep aquifer. Groundwater samples were collected from a deep well drilled down to 1500 m every six months (five times in total) after completion of deep well construction and the start of groundwater pumping. Next-generation sequencing and clone-library analyses of 16S rRNA genes were used to describe the subterranean microbial communities in the samples. The archaea: the prokaryote ratio in groundwater increased significantly from 1 to 7% (0 and 7 months after initiating groundwater pumping) to 59 to 72% (13, 19, and 26 months after initiating groundwater pumping), and dominant prokaryotes changed from fermentative bacteria to sulfate-reducing archaea. The optimal growth temperature of the sulfate-reducing archaea, estimated based on the guanine-plus-cytosine contents of their 16S rRNA genes, was 48-52 °C, which agreed well with the groundwater temperature at the deep-well outflow. Our results indicated that, in deep aquifers, groundwater pumping enhances groundwater flow, and the supply of sulfate-containing seawater activates the metabolism of thermophilic sulfate-reducing archaea.

Modelling the low temperature growth boundaries of Salmonella Enteritidis in raw and pasteurized egg yolk, egg white and liquid whole egg: Influence of the initial concentration.

Salmonella is the most frequently reported cause of foodborne outbreaks with known origin in Europe, with eggs and egg products standing out as the most frequent food source (when it was known). The growth and survival of Salmonella in eggs and egg products have been extensively studied and, recently, it has been reported that factors such as the initial concentration and thermal history of the egg product can also influence its growth capability. Therefore, the objective of this study was to define the boundary zones of the growth/no growth domain of Salmonella Enteritidis (4 strains) as a function of temperature (low temperature boundary) and the initial concentration in different egg products. A series of polynomial logistic regression equations were successfully adjusted, allowing the study of these factors and their interaction on the probability of growth of S. Enteritidis in these products. Results obtained indicate that the minimum growth temperatures of Salmonella Enteritidis are higher in egg white (9.5-18.3 °C) than in egg yolk (7.1-7.8 °C) or liquid whole egg (7.2-7.9 °C). Results also demonstrate that in raw liquid whole egg and raw and pasteurized egg white, the minimum growth temperature of Salmonella Enteritidis does depend on the initial concentration. Similarly, the previous thermal history of the egg product only influenced the minimum growth temperature in some of them. On the other hand, large differences in the minimum growth temperatures among strains were observed in some products (up to approx. 6 °C in egg white). Finally, it should be noted that none of the strains grew at 5 °C under any of the conditions assayed. Therefore, storage of egg products (particularly whole liquid egg and egg yolk) below this temperature might be regarded/proposed as a good management approach. Our experimental approach has allowed us to provide a more accurate prediction of S. Enteritidis minimum growth temperatures in egg products by taking into account additional factors (initial concentration and thermal history) while also providing a quantification of the intra-specie variability. This would be of high relevance for improving the safety of egg products.

Airborne survival and stress response in Listeria monocytogenes across different growth temperatures.

In the food industry, ensuring food safety during transportation and storage is vital, with temperature regulation preventing spoilage. However, airborne contamination through foodborne pathogens remains a concern. Listeria monocytogenes, a psychrotolerant foodborne pathogen, has been linked to various foodborne outbreaks. Therefore, understanding how its airborne characteristics depend on the growth temperature is imperative. As a result, when the L. monocytogenes was floated in air for 30 and 60 min, the surviving population of 15 °C-grown L. monocytogenes that was suspended in air and attached on the surface was significantly higher than L. monocytogenes grown at 25°C and 37 °C. The fatty acid analysis revealed a significantly higher proportion of shorter chain fatty acids in L. monocytogenes grown at 15 °C compared to those grown at 37 °C. Under aerosolization, L. monocytogenes encountered osmotic and cold stresses regardless of their growth temperature. Transcriptomic analysis showed that stress response related genes, such as oxidative and cold stress response, as well as PTS system related genes were upregulated at 15 °C, resulting in the enhanced resistance to various stresses during aerosolization. These results provide insights into the different responses of aerosolized L. monocytogenes according to the different growth temperatures, highlighting a critical factor in preventing airborne cross-contamination.

Leaf hydraulic properties of Antarctic plants: effects of growth temperature and its coordination with photosynthesis.

One of the well-documented effects of regional warming in Antarctica is the impact on flora. Warmer conditions modify several leaf anatomical traits of Antarctic vascular plants, increasing photosynthesis and growth. Given that CO2 and water vapor partially share their diffusion pathways through the leaf, changes in leaf anatomy could also affect the hydraulic traits of Antarctic plants. We evaluated the effects of growth temperature on several anatomical and hydraulic parameters of Antarctic plants and assessed the trait co-variation between these parameters and photosynthetic performance. Warmer conditions promoted an increase in leaf and whole plant hydraulic conductivity, correlating with adjustments in carbon assimilation. These adjustments were consistent with changes in leaf vasculature, where Antarctic species displayed different strategies. At higher temperature, Colobanthus quitensis decreased the number of leaf xylem vessels, but increased their diameter. In contrast, in Deschampsia antarctica the diameter did not change, but the number of vessels increased. Despite this contrasting behavior, some traits such as a small leaf diameter of vessels and a high cell wall rigidity were maintained in both species, suggesting a water-conservation response associated with the ability of Antarctic plants to cope with harsh environments.

Life Cycle Plasticity in Typhula and Pistillaria in the Arctic and the Temperate Zone.

Typhulaceae Jülich is one of the cold-adapted fungal families in basidiomycetes. The representative genera, Typhula (Pers.) Fr. and Pistillaria Fr., are distinguished by the discontinuity between stems and hymenia in the former and the continuity in the latter (Fries 1821). This taxonomic criterion is ambiguous, and consequently, the view of Karsten (1882) has been widely accepted: Typhula develops basidiomata from sclerotia, while basidiomata develop directly from substrata in Pistillaris. However, Corner (1970) observed basidiomata of Pistillaria petasitis S. Imai developing from sclerotia in Hokkaido, Japan. We later recognized that P. petasitis basidiomata also emerged directly from substrates on the ground in Hokkaido. An aberrant form of Typhula hyperborea H. Ekstr. was found in Upernavik, West Greenland. This specimen had a stem-like structure on a Poaceae plant, and sclerotia developed on its tip. Similar phenomena were found in other Typhula species in Japan. In this study, we aimed to elucidate the life cycle plasticity in the genera Typhula and Pistillaria through the interactions between their ecophysiological potential and environmental conditions in their localities. We collected and prepared strains of the above fungi from sclerotia or basidiomata, and we elucidated the taxonomical relationship and determined the physiological characteristics of our strains. Our findings imply that both Typhula and Pistillaria have the potential to produce sclerotia as well as the capacity for mycelial growth at ambient air temperatures in each locality where samples were collected. These findings suggest that Typhula spp. develope basidiomata not only from the sclerotia dispersed by the basidiospores but also from mycelia generated by the spore germination, which formed basidiomata multiple times, depending on their growth environments.

Effect of growth temperature on self-rectifying BaTiO3/ZnO heterojunction for high-density crossbar arrays and neuromorphic computing.

In the quest for high-density integration and massive scalability, ferroelectric-based devices provide an achievable approach for nonvolatile crossbar array (CBA) architecture and neuromorphic computing. In this report, ferroelectric-semiconductor (Pt/BaTiO3/ZnO/Au) heterojunction-based devices are demonstrated to exhibit nonvolatile and synaptic characteristics. In this study, the ferroelectric (BaTiO3) layer was modulated at various growth temperatures of 350 °C, 450 °C, 550 °C and 650 °C. Growing temperature in the ferroelectric layer has a significant impact on resistive switching. The ferroelectricity of the BaTiO3 thin film enhanced by increasing temperature causes a substantial shift in the interface state density at heterojunction interface, which is crucial for self-rectification. Furthermore, this self-rectifying property advances to reduce the crosstalk problem without any selector device. Enhanced resistive switching and neuromorphic applications have been demonstrated using BaTiO3 heterostructure devices at 550 °C. The dynamic ferroelectric polarization switching in this heterojunction demonstrated linear conductance change in artificial synapses with 91 % recognition accuracy. Ferroelectric polarization reversal with a depletion region at the heterojunction interface is the responsible mechanism for the switching in these devices. Thus, these findings pave the way for designing low power high-density crossbar arrays and neuromorphic application based on ferroelectric-semiconductor heterostructures.

Annealing-Modulated Surface Reconstruction for Self-Assembly of High-Density Uniform InAs/GaAs Quantum Dots on Large Wafers Substrate.

In this work, we developed pre-grown annealing to form ß2 reconstruction sites among ß or α (2 × 4) reconstruction phase to promote nucleation for high-density, size/wafer-uniform, photoluminescence (PL)-optimal InAs quantum dot (QD) growth on a large GaAs wafer. Using this, the QD density reached 580 (860) µm-2 at a room-temperature (T) spectral FWHM of 34 (41) meV at the wafer center (and surrounding) (high-rate low-T growth). The smallest FWHM reached 23.6 (24.9) meV at a density of 190 (260) µm-2 (low-rate high-T). The mediate rate formed uniform QDs in the traditional ß phase, at a density of 320 (400) µm-2 and a spectral FWHM of 28 (34) meV, while size-diverse QDs formed in ß2 at a spectral FWHM of 92 (68) meV and a density of 370 (440) µm-2. From atomic-force-microscope QD height distribution and T-dependent PL spectroscopy, it is found that compared to the dense QDs grown in ß phase (mediate rate, 320 µm-2) with the most large dots (240 µm-2), the dense QDs grown in ß2 phase (580 µm-2) show many small dots with inter-dot coupling in favor of unsaturated filling and high injection to large dots for PL. The controllable annealing (T, duration) forms ß2 or ß2-mixed α or ß phase in favor of a wafer-uniform dot island and the faster T change enables optimal T for QD growth.

Higher-temperature-adapted dengue virus serotype 2 strain exhibits enhanced virulence in AG129 mouse model.

The factors that drive dengue virus (DENV) evolution, and selection of virulent variants are yet not clear. Higher environmental temperature shortens DENV extrinsic incubation period in mosquitoes, increases human transmission, and plays a critical role in outbreak dynamics. In the present study, we looked at the effect of temperature in altering the virus virulence. We found that DENV cultured at a higher temperature in C6/36 mosquito cells was significantly more virulent than the virus grown at a lower temperature. In a mouse model, the virulent strain induced enhanced viremia and aggressive disease with a short course, hemorrhage, severe vascular permeability, and death. Higher inflammatory cytokine response, thrombocytopenia, and severe histopathological changes in vital organs such as heart, liver, and kidney were hallmarks of the disease. Importantly, it required only a few passages for the virus to acquire a quasi-species population harboring virulence-imparting mutations. Whole genome comparison with a lower temperature passaged strain identified key genomic changes in the structural protein-coding regions as well as in the 3'UTR of the viral genome. Our results point out that virulence-enhancing genetic changes could occur in the dengue virus genome under enhanced growth temperature conditions in mosquito cells.

Main Factors Shaping Amino Acid Usage Across Evolution.

The standard genetic code determines that in most species, including viruses, there are 20 amino acids that are coded by 61 codons, while the other three codons are stop triplets. Considering the whole proteome each species features its own amino acid frequencies, given the slow rate of change, closely related species display similar GC content and amino acids usage. In contrast, distantly related species display different amino acid frequencies. Furthermore, within certain multicellular species, as mammals, intragenomic differences in the usage of amino acids are evident. In this communication, we shall summarize some of the most prominent and well-established factors that determine the differences found in the amino acid usage, both across evolution and intragenomically.

Increased growth temperature and vitamin B12 supplementation reduces the lag time for rapid pathogen identification in BHI agar and blood cultures.

Background: The rapid diagnostics of pathogens is essential to prescribe appropriate and early antibiotic therapy. The current methods for pathogen detection require the bacteria to grow in a culture medium, which is time-consuming. This increases the mortality rate and the global burden of antimicrobial resistance. Culture-free detection methods are still under development and are not used in the clinical routine. Therefore decreasing the culture time for accurate detection of infection and resistance is vital for diagnosis. Methods: In this study, we wanted to investigate easy-to-implement factors (in a minimal laboratory set-up), including inoculum size, incubation temperature, and additional supplementation ( e.g., vitamin B12 and trace metals), that can significantly reduce the lag time (t lag). These factors were arranged in simple two-level factorial designs using Gram-positive ( Escherichia coli and Pseudomonas aeruginosa) and Gram-negative ( Staphylococcus aureus and Bacillus subtilis) bacteria, including clinical isolates with known antimicrobial resistance profiles. Blood samples spiked with a clinical isolate of E. coli CCUG17620 were also tested to see the effect of elevated incubation temperature on bacterial growth in blood cultures. Results: We observed that increased incubation temperature (42°C) along with vitamin B12 supplementation significantly reduced the t lag (10 - 115 minutes or 4% - 49%) in pure clinical isolates and blood samples spiked with E. coli CCUG17620. In the case of the blood sample, PCR results also detected bacterial DNA after only 3h of incubation and at three times the CFU/mL. Conclusions: Enrichment of bacterial culture media with growth supplements such as vitamin B12 and increased incubation temperature can be a cheap and rapid method for the early detection of pathogens. This is a proof-of-concept study restricted to a few bacterial strains and growth conditions. In the future, the effect of other growth conditions and difficult-to-culture bacteria should be explored to shorten the lag phase.

Identifying phytopathogenic fungi in Al-Baha province, Saudi Arabia through their molecular and morphological features: An overview.

Fungi are major pathogens of plants. They are responsible for most of the spoilage that occurs to plants in fields or in storage conditions. In addition to the direct impacts of fungi upon the plant's fruiting body, such as leaf spot, wilt, rust, dieback and rot, fungi can contaminate plants with mycotoxins. Twenty isolates were molecularly identified in this study representing eight genera and twelve species. The most common species identified in this work belongs to Aspergillus (33.3%), Penicillium (16.6%) and Fusarium (16.6%) genera, which are well known to have mycotoxigenic species. Environmental factors have a significant influence on the biological activity of fungi, including growth, sporulation and mycotoxin production. Temperature and water activity affect fungal virulence factors, such as growth, colonisation, spread and mycotoxin production. This work found the optimal temperature for the growth of isolates, was 30 °C for 75 % of isolates and at 25 °C for 25 % of isolates. This information is useful, as it helps to identify the phytopathogenic and mycotoxigenic species, and determining optimal growth temperatures is important to control them and reduce their threats.

Neglecting acclimation of photosynthesis under drought can cause significant errors in predicting leaf photosynthesis in wheat.

Extreme climatic events, such as heat waves, cold snaps and drought spells, related to global climate change, have become more frequent and intense in recent years. Acclimation of plant physiological processes to changes in environmental conditions is a key component of plant adaptation to climate change. We assessed the temperature response of leaf photosynthetic parameters in wheat grown under contrasting water regimes and growth temperatures (Tgrowth ). Two independent experiments were conducted under controlled conditions. In Experiment 1, two wheat genotypes were subjected to well-watered or drought-stressed treatments; in Experiment 2, the two water regimes combined with high, medium and low Tgrowth were imposed on one genotype. Parameters of a biochemical C3 -photosynthesis model were estimated at six leaf temperatures for each factor combination. Photosynthesis acclimated more to drought than to Tgrowth . Drought affected photosynthesis by lowering its optimum temperature (Topt ) and the values at Topt of light-saturated net photosynthesis, stomatal conductance, mesophyll conductance, the maximum rate of electron transport (Jmax ) and the maximum rate of carboxylation by Rubisco (Vcmax ). Topt for Vcmax was up to 40°C under well-watered conditions but 24-34°C under drought. The decrease in photosynthesis under drought varied among Tgrowth but was similar between genotypes. The temperature response of photosynthetic quantum yield under drought was partly attributed to photorespiration but more to alternative electron transport. All these changes in biochemical parameters could not be fully explained by the changed leaf nitrogen content. Further model analysis showed that both diffusional and biochemical parameters of photosynthesis and their thermal sensitivity acclimate little to Tgrowth , but acclimate considerably to drought and the combination of drought and Tgrowth . The commonly used modelling approaches, which typically consider the response of diffusional parameters, but ignore acclimation responses of biochemical parameters to drought and Tgrowth , strongly overestimate leaf photosynthesis under variable temperature and drought.

Effects of growth temperature on multi-scale structure of root tuber starch in sweet potato.

Sweet potato was planted at three soil and air temperatures (21, 25 and 28 °C) with the same humidity and light time/intensity. Root tuber starches were isolated, and their multi-scale structures were investigated to reveal the effects of growth temperature on starch properties. Growth temperature did not change the morphology and amylose content of starch, but markedly increased the size of starch from volume-weighted mean diameter 12.2 µm to 17.0 µm. Starch grown at high growth temperature exhibited less A branch-chains and lower branching degree of amylopectin and more B2 and B3+ branch-chains of amylopectin than at low growth temperature. With increasing growth temperature, starch changed from CC-type to CA-type, its relative crystallinity and lamellar peak intensity increased, and the thickness of crystalline and amorphous lamellae did not significantly change. Starch grown at high growth temperature exhibited significantly higher gelatinization temperature than at low growth temperature, but had similar gelatinization enthalpy.

A Plasmid-Based Fluorescence Reporter System for Monitoring Oxidative Damage in E. coli.

Quantitating intracellular oxidative damage caused by reactive oxygen species (ROS) is of interest in many fields of biological research. The current systems primarily rely on supplemented oxygen-sensitive substrates that penetrate the target cells, and react with ROS to produce signals that can be monitored with spectroscopic or imaging techniques. The objective here was to design a new non-invasive analytical strategy for measuring ROS-induced damage inside living cells by taking advantage of the native redox sensor system of E. coli. The developed plasmid-based sensor relies on an oxygen-sensitive transcriptional repressor IscR that controls the expression of a fluorescent marker in vivo. The system was shown to quantitatively respond to oxidative stress induced by supplemented H2O2 and lowered cultivation temperatures. Comparative analysis with fluorescence microscopy further demonstrated that the specificity of the reporter system was equivalent to the commercial chemical probe (CellROX). The strategy introduced here is not dependent on chemical probes, but instead uses a fluorescent expression system to detect enzyme-level oxidative damage in microbial cells. This provides a cheap and simple means for analysing enzyme-level oxidative damage in a biological context in E. coli.

The Umbelopsis ramanniana Sensu Lato Consists of Five Cryptic Species.

Umbelopsis ramanniana is one of the most commonly reported species within the genus and an important oleaginous fungus. The morphology of the species varies remarkably in sporangiospores, columellae and chlamydospores. However, phylogenetic analyses based on ITS and nLSU rDNA had previously shown insufficiency in achieving species level identification in the genus Umbelopsis. In this study, by applying a polyphasic approach involving multi-gene (nSSU, ITS, nLSU, act1, MCM7 and cox1) phylogeny, morphology and maximum growth temperature, U. ramanniana sensu lato was revealed as a polyphyletic group and resolved with five novel taxa, namely U. curvata, U. dura, U. macrospora, U. microsporangia and U. oblongielliptica. Additionally, a key for all currently accepted species in Umbelopsis was also updated.

Microbial maintenance energy quantified and modeled with microcalorimetry.

Refining the energetic costs of cellular maintenance is essential for predicting microbial growth and survival in the environment. Here, we evaluate a simple batch culture method to quantify energy partitioning between growth and maintenance using microcalorimetry and thermodynamic modeling. The constants derived from the batch culture system were comparable to those that have been reported from meta-analyses of data derived from chemostat studies. The model accurately predicted temperature-dependent biomass yield and the upper temperature limit of growth for Desulfovibrio alaskensis G20, suggesting the method may have broad application. An Arrhenius temperature dependence for the specific energy consumption rate, inferred from substrate consumption and heat evolution, was observed over the entire viable temperature range. By combining this relationship for specific energy consumption rates and observed specific growth rates, the model describes an increase in nongrowth associated maintenance at higher temperatures and the corresponding decrease in energy available for growth. This analytical and thermodynamic formulation suggests that simply monitoring heat evolution in batch culture could be a useful complement to the recognized limitations of estimating maintenance using extrapolation to zero growth in chemostats.

Growth temperature-induced changes in resistance of Listeria monocytogenes and Yersinia enterocolitica to X-ray irradiation.

This study aimed to evaluate the effect of different growth temperatures on the resistance of Listeria monocytogenes and Yersinia enterocolitica to low-energy X-ray irradiation and elucidate the mechanisms of resistance variability. The X-ray treatment at a dose of 1.0 kGy resulted in 4.00-, 4.87-, 3.98-, and 2.27-log reductions in cell counts of L. monocytogenes cultured at 37, 25, 15, and 4 °C, respectively. Cell counts of Y. enterocolitica, cultured at 37, 25, 15, and 4 °C, in phosphate-buffered saline decreased by 3.96, 4.98, 3.79, and 3.25 log CFU/mL, respectively, after X-ray irradiation at 0.4 kGy. In addition, the increased resistance to X-rays at low temperatures (4 °C) was induced by different mechanisms in the two pathogens. The results reveal that the key mechanisms for the change in resistance of L. monocytogenes and Y. enterocolitica to X-ray irradiation under different growth temperatures are efflux pump malfunction and DNA damage, respectively. These results suggest that the stress resistance status of L. monocytogenes and Y. enterocolitica cultured at different growth temperatures (37, 25, 15, and 4 °C) should be considered for application in low-dose X-ray irradiation in the food industry.

The pre-induction temperature affects recombinant HuGM-CSF aggregation in thermoinducible Escherichia coli.

The overproduction of recombinant proteins in Escherichia coli leads to insoluble aggregates of proteins called inclusion bodies (IBs). IBs are considered dynamic entities that harbor high percentages of the recombinant protein, which can be found in different conformational states. The production conditions influence the properties of IBs and recombinant protein recovery and solubilization. The E. coli growth in thermoinduced systems is generally carried out at 30 °C and then recombinant protein production at 42 °C. Since the heat shock response in E. coli is triggered above 34 °C, the synthesis of heat shock proteins can modify the yields of the recombinant protein and the structural quality of IBs. The objective of this work was to evaluate the effect of different pre-induction temperatures (30 and 34 °C) on the growth of E. coli W3110 producing the human granulocyte-macrophage colony-stimulating factor (rHuGM-CSF) and on the IBs structure in a λpL/pR-cI857 thermoinducible system. The recombinant E. coli cultures growing at 34 °C showed a ~ 69% increase in the specific growth rate compared to cultures grown at 30 °C. The amount of rHuGM-CSF in IBs was significantly higher in cultures grown at 34 °C. Main folding chaperones (DnaK and GroEL) were associated with IBs and their co-chaperones (DnaJ and GroES) with the soluble protein fraction. Finally, IBs from cultures that grew at 34 °C had a lower content of amyloid-like structure and were more sensitive to proteolytic degradation than IBs obtained from cultures at 30 °C. Our study presents evidence that increasing the pre-induction temperature in a thermoinduced system allows obtaining higher recombinant protein and reducing amyloid contents of the IBs. KEY POINTS: • Pre-induction temperature determines inclusion bodies architecture • In pre-induction (above 34 °C), the heat shock response increases recombinant protein production • Inclusion bodies at higher pre-induction temperature show a lower amyloid content.

Molecular Phylogenetic Study of Strains Morphologically Identified as Exophiala dermatitidis from Clinical and Environmental Specimens in Japan.

In this study, we aimed to clarify the phylogenetic distribution of Exophiala dermatitidis in Japan and describe the characteristics of genotypes. We examined 67 clinical and environmental isolates that were morphologically identified and preserved as E. dermatitidis and we confirmed the identification on the basis of the ribosomal DNA internal transcribed spacer region. Genotype sequences were aligned and compared using maximum likelihood phylogenetic tree analyses of the ITS1 region. Additionally, the strains of each genotype were tested for mycological characteristics, such as growth temperature, growth rate, and drug sensitivity. The 67 strains examined were isolated from Japan, the United States, Brazil, Venezuela, and China. In accordance with the establishment of a phylogenetic tree for the ITS1 region, 45 of the 49 Japanese strains were classified as genotype A, two as genotype B, and two as genotype D (A2 according to the method of Matos et al. (2003)). Chinese strains were divided into genotypes A and D (A2), and South American strains were classified into genotypes A, B, B2, and C2, while all strains from the U.S. belonged to genotype A. New genotype groups B2 and C2 were identified in Brazilian and Venezuelan strains, respectively. There were no specific differences among the genotypes or isolated regions in the antifungal susceptibility test for all E. dermatitidis isolates. However, genotypes B2 and D (A2) exhibited growth at higher temperatures than the other genotypes.

Precipitous Increase of Bacterial CRISPR-Cas Abundance at Around 45°C.

Although performing adaptive immunity, CRISPR-Cas systems are present in only 40% of bacterial genomes. We observed an abrupt increase of bacterial CRISPR-Cas abundance at around 45°C. Phylogenetic comparative analyses confirmed that the abundance correlates with growth temperature only at the temperature range around 45°C. From the literature, we noticed that the diversities of cellular predators (like protozoa, nematodes, and myxobacteria) have a steep decline at this temperature range. The grazing risk faced by bacteria reduces substantially at around 45°C and almost disappears above 60°C. We propose that viral lysis would become the dominating factor of bacterial mortality, and antivirus immunity has a higher priority at higher temperatures. In temperature ranges where the abundance of cellular predators does not change with temperature, the growth temperatures of bacteria would not significantly affect their CRISPR-Cas contents. The hypothesis predicts that bacteria should also be rich in CRISPR-Cas systems if they live in other extreme conditions inaccessible to grazing predators.