Toward a Mechanistic Understanding of Bacterial Rod Shape Formation and Regulation.

One of the most common bacterial shapes is a rod, yet we have a limited understanding of how this simple shape is constructed. While only six proteins are required for rod shape, we are just beginning to understand how they self-organize to build the micron-sized enveloping structures that define bacterial shape out of nanometer-sized glycan strains. Here, we detail and summarize the insights gained over the last 20 years into this complex problem that have been achieved with a wide variety of different approaches. We also explain and compare both current and past models of rod shape formation and maintenance and then highlight recent insights into how the Rod complex might be regulated.

Asymmetric winter warming reduces microbial carbon use efficiency and growth more than symmetric year-round warming in alpine soils.

Asymmetric seasonal warming trends are evident across terrestrial ecosystems, with winter temperatures rising more than summer ones. Yet, the impact of such asymmetric seasonal warming on soil microbial carbon metabolism and growth remains poorly understood. Using 18O isotope labeling, we examined the effects of a decade-long experimental seasonal warming on microbial carbon use efficiency (CUE) and growth in alpine grassland ecosystems. Moreover, the quantitative stable isotope probing with 18O-H2O was employed to evaluate taxon-specific bacterial growth in these ecosystems. Results show that symmetric year-round warming decreased microbial growth rate by 31% and CUE by 22%. Asymmetric winter warming resulted in a further decrease in microbial growth rate of 27% and microbial CUE of 59% compared to symmetric year-round warming. Long-term warming increased microbial carbon limitations, especially under asymmetric winter warming. Long-term warming suppressed the growth rates of most bacterial genera, with asymmetric winter warming having a stronger inhibition on the growth rates of specific genera (e.g., Gp10, Actinomarinicola, Bosea, Acidibacter, and Gemmata) compared to symmetric year-round warming. Bacterial growth was phylogenetically conserved, but this conservation diminished under warming conditions, primarily due to shifts in bacterial physiological states rather than the number of bacterial species and community composition. Overall, long-term warming escalated microbial carbon limitations, decreased microbial growth and CUE, with asymmetric winter warming having a more pronounced effect. Understanding these impacts is crucial for predicting soil carbon cycling as global warming progresses.

Machine learning identifies key metabolic reactions in bacterial growth on different carbon sources.

Carbon source-dependent control of bacterial growth is fundamental to bacterial physiology and survival. However, pinpointing the metabolic steps important for cell growth is challenging due to the complexity of cellular networks. Here, the elastic net model and multilayer perception model that integrated genome-wide gene-deletion data and simulated flux distributions were constructed to identify metabolic reactions beneficial or detrimental to Escherichia coli grown on 30 different carbon sources. Both models outperformed traditional in silico methods by identifying not just essential reactions but also nonessential ones that promote growth. They successfully predicted metabolic reactions beneficial to cell growth, with high convergence between the models. The models revealed that biosynthetic pathways generally promote growth across various carbon sources, whereas the impact of energy-generating pathways varies with the carbon source. Intriguing predictions were experimentally validated for findings beyond experimental training data and the impact of various carbon sources on the glyoxylate shunt, pyruvate dehydrogenase reaction, and redundant purine biosynthesis reactions. These highlight the practical significance and predictive power of the models for understanding and engineering microbial metabolism.

Coupling of Ribosome Synthesis and Translational Capacity with Cell Growth.

Ribosome and protein synthesis lie at the core of cell growth and are major consumers of the cellular budget. Here we review recent progress in the coupling of ribosome synthesis and translational capacity with cell growth in bacteria. We elaborate on the different strategies of bacteria to modulate the protein synthesis rate at fast and slow growth rates. In particular, bacterial cells maintain translational potential at very slow growth as a strategy to keep fitness in fluctuating environments. We further discuss the important role of ribosome synthesis in rapidly proliferating eukaryotic cells such as yeast cells and cancer cells. The tight relation between ribosome and cell growth provides a broad research avenue for researchers from various disciplines.

Microbial Primer: Bacterial growth kinetics.

tGrowth of microorganisms and interpretation of growth data are core skills required by microbiologists. While science moves forward, it is of paramount importance that essential skills are not lost. The bacterial growth curve and the information that can gleaned from it is of great value to all of microbiology, whether this be a simple growth experiment, comparison of mutant strains or the establishment of conditions for a large-scale multi-omics experiment. Increasingly, the basics of plotting and interpreting growth curves and growth data are being overlooked. This primer article serves as a refresher for microbiologists on the fundamentals of microbial growth kinetics.

Measuring differential fitness costs and interactions between genetic cassettes using fluorescent spectrophotometry.

In this article, we present a method for designing, executing, and analyzing data from a microbial competition experiment. We use fluorescent reporters to label different competing strains and resolve individual growth curves using a fluorescent spectrophotometer. Our comprehensive data analysis pipeline integrates multiple experiments to simultaneously infer sources of variation, extract selection coefficients, and estimate the genetic contributions to fitness for various synthetic genetic cassettes (SGCs). To demonstrate the method, we employ a synthetic biological system based on Escherichia coli. Strains carry 1 of 10 different plasmids and one of three genomically integrated fluorescent markers. All strains are co-cultured to obtain real-time measurements of optical density (total population density) and fluorescence (sub-population densities). We identify challenges in calibrating between fluorescence and density and of fluorescent proteins maturing at different rates. To resolve these issues, we compare two methods of fluorescence calibration and correct for maturation by measuring in vivo maturation times. We provide evidence of genetic interactions occurring between our SGCs and further show how to use our statistical model to test some hypotheses about microbial growth and the costs of protein expression.IMPORTANCEFluorescently labeled co-cultures are becoming increasingly popular. The approach proposed here offers a high standard for experimental design and data analysis to measure selection coefficients and growth rates in competition. Measuring competitive differences is useful in many laboratory studies, allowing for fitness cost-correction of growth rates and ecological interactions and testing hypotheses in synthetic biology. Using time-resolved growth curves, rather than endpoint measurements, for competition assays allows us to construct a detailed scientific model that can be used to ask questions about fine-grained phenomena, such as bacterial growth dynamics, as well as higher-level phenomena, such as the interactions between synthetic cassette expression.

A longitudinal study on the bacterial quality of baby spinach cultivated in Arizona and California.

In the U.S., baby spinach is mostly produced in Arizona (AZ) and California (CA). Characterizing the impact of growing region on the bacterial quality of baby spinach can inform quality management practices in industry. Between December 2021 and December 2022, baby spinach was sampled after harvest and packaging for microbiological testing, including shelf-life testing of packaged samples that were stored at 4°C. Samples were tested to (i) determine bacterial concentration, and (ii) obtain and identify bacterial isolates. Packaged samples from the Salinas, CA, area (n = 13), compared to those from the Yuma, AZ, area (n = 9), had a significantly higher bacterial concentration, on average, by 0.78 log10 CFU/g (P < 0.01, based on aerobic, mesophilic plate count data) or 0.67 log10 CFU/g (P < 0.01, based on psychrotolerant plate count data); the bacterial concentrations of harvest samples from the Yuma and Salinas areas were not significantly different. Our data also support that an increase in preharvest temperature is significantly associated with an increase in the bacterial concentration on harvested and packaged spinach. A Fisher's exact test and linear discriminant analysis (effect size), respectively, demonstrated that (i) the genera of 2,186 bacterial isolates were associated (P < 0.01) with growing region and (ii) Pseudomonas spp. and Exiguobacterium spp. were enriched in spinach from the Yuma and Salinas areas, respectively. Our findings provide preliminary evidence that growing region and preharvest temperature may impact the bacterial quality of spinach and thus could inform more targeted strategies to manage produce quality. IMPORTANCE: In the U.S., most spinach is produced in Arizona (AZ) and California (CA) seasonally; typically, spinach is cultivated in the Yuma, AZ, area during the winter and in the Salinas, CA, area during the summer. As the bacterial quality of baby spinach can influence consumer acceptance of the product, it is important to assess whether the bacterial quality of baby spinach can vary between spinach-growing regions. The findings of this study provide insights that could be used to support region-specific quality management strategies for baby spinach. Our results also highlight the value of further evaluating the impact of growing region and preharvest temperature on the bacterial quality of different produce commodities.

Use of Cyrene™, as an alternative to dimethyl sulfoxide, as a diluent for Melatonin to determine its in vitro antimicrobial capacity.

Melatonin (MLT) is a methoxyindole that has potent antioxidant actions, anti-inflammatory, and antiapoptotic capacity. However, its in vitro antibacterial capacity has been the least studied of its properties. Dimethylsulfoxide (DMSO) has been the most used solvent for these tests, but it shows an antimicrobial effect if it is not dissolved. Cyrene™ is a new solvent that has emerged as an alternative to DMSO. Therefore, this study aimed to determine the antimicrobial capacity of MLT by MIC assays, using Cyrene™ as a solvent. Likewise, the solubility of MLT in this solvent and whether it exerted any effect on bacterial growth at different percentages was also determined. Different dilutions of MLT in Cyrene™ with different concentrations, were prepared. No growth inhibition caused by MLT was observed. The growth inhibition observed was because of Cyrene™. The maximum amount of MLT that can be diluted in 100% Cyrene is 10 mg/mL, but this percentage of solvent shows a bactericidal effect. Therefore, it must be dissolved at 5% to avoid this effect, so only 4 mg/mL of MLT can be diluted in it. Therefore, if no other solvents are available, the in vitro antibacterial role of MLT cannot be adequately assessed.

Proliferation of psychrotrophic bacteria in cold-stored platelet concentrates.

BACKGROUND AND OBJECTIVES: Platelet concentrates (PC) are stored at 20-24°C to maintain platelet functionality, which may promote growth of contaminant bacteria. Alternatively, cold storage of PC limits bacterial growth; however, data related to proliferation of psychotrophic species in cold-stored PC (CSP) are scarce, which is addressed in this study. MATERIALS AND METHODS: Eight laboratories participated in this study with a pool/split approach. Two split PC units were spiked with ~25 colony forming units (CFU)/PC of Staphylococcus aureus, Klebsiella pneumoniae, Serratia liquefaciens, Pseudomonas fluorescens and Listeria monocytogenes. One unit was stored under agitation at 20-24°C/7 days while the second was stored at 1-6°C/no agitation for 21 days. PC were sampled periodically to determine bacterial loads. Five laboratories repeated the study with PC inoculated with lyophilized inocula (~30 CFU/mL) of S. aureus and K. pneumoniae. RESULTS: All species proliferated in PC stored at 20-24°C, reaching concentrations of ≤109 CFU/mL by day 7. Psychrotrophic P. fluorescens and S. liquefaciens proliferated in CSP to ~106 CFU/mL and ~105 CFU/mL on days 10 and 17 of storage, respectively, followed by L. monocytogenes, which reached ~102 CFU/mL on day 21. S. aureus and K. pneumoniae did not grow in CSP. CONCLUSION: Psychrotrophic bacteria, which are relatively rare contaminants in PC, proliferated in CSP, with P. fluorescens reaching clinically significant levels (≥105 CFU/mL) before day 14 of storage. Cold storage reduces bacterial risk of PC to levels comparable with RBC units. Safety of CSP could be further improved by implementing bacterial detection systems or pathogen reduction technologies if storage is beyond 10 days.

Unlocking the genome of the non-sourdough Kazachstania humilis MAW1: insights into inhibitory factors and phenotypic properties.

BACKGROUND: Ascomycetous budding yeasts are ubiquitous environmental microorganisms important in food production and medicine. Due to recent intensive genomic research, the taxonomy of yeast is becoming more organized based on the identification of monophyletic taxa. This includes genera important to humans, such as Kazachstania. Until now, Kazachstania humilis (previously Candida humilis) was regarded as a sourdough-specific yeast. In addition, any antibacterial activity has not been associated with this species. RESULTS: Previously, we isolated a yeast strain that impaired bio-hydrogen production in a dark fermentation bioreactor and inhibited the growth of Gram-positive and Gram-negative bacteria. Here, using next generation sequencing technologies, we sequenced the genome of this strain named K. humilis MAW1. This is the first genome of a K. humilis isolate not originating from a fermented food. We used novel phylogenetic approach employing the 18 S-ITS-D1-D2 region to show the placement of the K. humilis MAW1 among other members of the Kazachstania genus. This strain was examined by global phenotypic profiling, including carbon sources utilized and the influence of stress conditions on growth. Using the well-recognized bacterial model Escherichia coli AB1157, we show that K. humilis MAW1 cultivated in an acidic medium inhibits bacterial growth by the disturbance of cell division, manifested by filament formation. To gain a greater understanding of the inhibitory effect of K. humilis MAW1, we selected 23 yeast proteins with recognized toxic activity against bacteria and used them for Blast searches of the K. humilis MAW1 genome assembly. The resulting panel of genes present in the K. humilis MAW1 genome included those encoding the 1,3-ß-glucan glycosidase and the 1,3-ß-glucan synthesis inhibitor that might disturb the bacterial cell envelope structures. CONCLUSIONS: We characterized a non-sourdough-derived strain of K. humilis, including its genome sequence and physiological aspects. The MAW1, together with other K. humilis strains, shows the new organization of the mating-type locus. The revealed here pH-dependent ability to inhibit bacterial growth has not been previously recognized in this species. Our study contributes to the building of genome sequence-based classification systems; better understanding of K.humilis as a cell factory in fermentation processes and exploring bacteria-yeast interactions in microbial communities.

Temperature Adaptation of Aquatic Bacterial Community Growth Is Faster in Response to Rising than to Falling Temperature.

Bacteria are key organisms in energy and nutrient cycles, and predicting the effects of temperature change on bacterial activity is important in assessing global change effects. A changing in situ temperature will affect the temperature adaptation of bacterial growth in lake water, both long term in response to global change, and short term in response to seasonal variations. The rate of adaptation may, however, depend on whether temperature is increasing or decreasing, since bacterial growth and turnover scale with temperature. Temperature adaptation was studied for winter (in situ temperature 2.5 °C) and summer communities (16.5 °C) from a temperate lake in Southern Sweden by exposing them to a temperature treatment gradient between 0 and 30 °C in ~ 5 °C increments. This resulted mainly in a temperature increase for the winter and a decrease for the summer community. Temperature adaptation of bacterial community growth was estimated as leucine incorporation using a temperature Sensitivity Index (SI, log growth at 35 °C/4 °C), where higher values indicate adaptation to higher temperatures. High treatment temperatures resulted in higher SI within days for the winter community, resulting in an expected level of community adaptation within 2 weeks. Adaptation for the summer community was also correlated to treatment temperature, but the rate of adaption was slower. Even after 5 weeks, the bacterial community had not fully adapted to the lowest temperature conditions. Thus, during periods of increasing temperature, the bacterial community will rapidly adapt to function optimally, while decreasing temperature may result in long periods of non-optimal functioning.

The Growth Yield of Aminobacter niigataensis MSH1 on the Micropollutant 2,6-Dichlorobenzamide Decreases Substantially at Trace Substrate Concentrations.

2,6-Dichlorobenzamide (BAM) is an omnipresent micropollutant in European groundwaters. Aminobacter niigataensis MSH1 is a prime candidate for biologically treating BAM-contaminated groundwater since this organism is capable of utilizing BAM as a carbon and energy source. However, detailed information on the BAM degradation kinetics by MSH1 at trace concentrations is lacking, while this knowledge is required for predicting and optimizing the degradation process. Contaminating assimilable organic carbon (AOC) in media makes the biodegradation experiment a mixed-substrate assay and hampers exploration of pollutant degradation at trace concentrations. In this study, we examined how the BAM concentration affects MSH1 growth and BAM substrate utilization kinetics in a AOC-restricted background to avoid mixed-substrate conditions. Conventional Monod kinetic models were unable to predict kinetic parameters at low concentrations from kinetics determined at high concentrations. Growth yields on BAM were concentration-dependent and decreased substantially at trace concentrations; i.e., growth of MSH1 diminished until undetectable levels at BAM concentrations below 217 µg-C/L. Nevertheless, BAM degradation continued. Decreasing growth yields at lower BAM concentrations might relate to physiological adaptations to low substrate availability or decreased expression of downstream steps of the BAM catabolic pathway beyond 2,6-dichlorobenzoic acid (2,6-DCBA) that ultimately leads to Krebs cycle intermediates for growth and energy conservation.

Potential Growth of Anammox Bacteria under Aerobic Conditions.

Anammox bacteria are obligate anaerobic bacteria that exist widely in nature with sufficient amounts of dissolved oxygen. However, whether anammox bacteria can grow under aerobic conditions remains unclear. In this study, we found that the production of nitrate in the anammox system under aerobic conditions was significantly higher than that under anaerobic conditions without total nitrogen loss. Anammox bacteria can grow by oxidizing nitrite and dehydrogenating hydrazine to produce electrons for carbon fixation. The hydrazine dehydrogenase in anammox bacteria was inhibited under aerobic conditions, and the nitrite oxidoreductase transcription expression of anammox bacteria increased by 2.7 times compared to that under anaerobic conditions, which was the main way for anammox bacteria perform carbon fixation. DNA-stable isotope probing with 13C bicarbonate found the existence of anammox bacteria with 13C isotopes in aerobic cultivation, further proving that anammox bacteria can grow under aerobic condition. More than half of the pathways in glycolysis, the Wood-Ljungdahl pathway, and the tricarboxylic acid cycle were upregulated in anammox bacteria in aerobic condition. Large amounts of bacterioferritins are the important antioxidative enzymes in anammox bacteria in the aerobic environment, which contributes to their stronger oxygen adaptation than other anaerobes. This study expands our understanding of the growth mechanism of anammox bacteria as well as the oxygen adaptation strategies of obligate anaerobic bacteria.

Bacteriology and clinical outcomes of urine mixed bacterial growth in pregnancy.

INTRODUCTION AND HYPOTHESIS: The objective was to analyse the risk of significant bacteriuria in repeat urine cultures from pregnant women, following initial mixed bacterial results. METHODS: This retrospective study examined maternal characteristics and clinical features of women who repeated urine cultures due to previous mixed cultures results. RESULTS: Of 262 women included, 80 (30.5%) had negative cultures and 125 (47.7%) had mixed bacterial growth in their repeat cultures. Positive results (≥104 CFU/ml of a urinary pathogen) were obtained for 57 women (21.8% [95% CI 17.1-27.0]). For 37 (14.1%), the repeat specimen grew 104-105 CFU/ml of microorganisms; whereas for 20 women (7.6% [95% CI 4.9-11.3]), it grew ≥105 CFU/ml. Among women with positive (>104 CFU/ml) compared with those with negative or mixed growth, rates of urinary symptoms were higher (38.6% vs 23.4%, p=0.028), abnormal dipstick results (49.1% vs 21.0%, p<0.001) and hydronephrosis, as demonstrated by renal ultrasound (12.3% vs 2.0, p=0.003). In a multivariate logistic regression analysis, hydronephrosis was associated with the occurrence of a positive repeat culture (aOR = 10.65, 95% CI 2.07-54.90). The sensitivity and specificity for predicting a repeat urine culture with ≥105 CFU/ml were 12.9% and 94.3% respectively, for urinary symptoms; and 19.7% and 97.4% respectively, for abnormal dipstick results. CONCLUSIONS: Mixed bacterial growth might represent a true urinary tract infection in a considerable proportion of women who are symptomatic and have an abnormal dipstick urinalysis.

Three distinct metabolic phases of polychlorinated biphenyls/biphenyl degrader Acidovorax sp. KKS102 in nutrient broth.

Acidovorax sp. KKS102 is a beta-proteobacterium capable of degrading polychlorinated biphenyls (PCBs). In this study, we examined its growth in liquid nutrient broth supplemented with different carbon sources. KKS102 had at least 3 distinct metabolic phases designated as metabolic phases 1-3, with phase 2 having 2 sub-phases. For example, succinate, fumarate, and glutamate, known to repress the PCB/biphenyl catabolic operon in KKS102, were utilized in phase 1, while acetate, arabinose, and glycerol in phase 2, and glucose and mannose in phase 3. We also showed that the BphQ response regulator mediating catabolite control in KKS102, whose expression level increased moderately through the growth, plays important roles in carbon metabolism in phases 2 and 3. Our study elucidates the hierarchical growth of KKS102 in nutrient-rich media. This insight is crucial for studies exploiting microbial biodegradation capabilities and advancing studies for catabolite regulation mechanisms.

Exploiting tropical fruit processing coproducts as circular resources to promote the growth and maintain the culturability and functionality of probiotic lactobacilli.

This study evaluated the use of acerola (Malpighia glabra L., CACE), cashew (Anacardium occidentale L., CCAS), and guava (Psidium guayaba L., CGUA) fruit processing coproducts as substrates to promote the growth, metabolite production, and maintenance of the viability/metabolic activity of the probiotics Lactobacillus acidophilus LA-05 and Lacticaseibacillus paracasei L-10 during cultivation, freeze-drying, storage, and exposure to simulated gastrointestinal digestion. Probiotic lactobacilli presented high viable counts (≥8.8 log colony-forming units (CFU)/mL) and a short lag phase during 24 h of cultivation in CACE, CCAS, and CGUA. Cultivation of probiotic lactobacilli in fruit coproducts promoted sugar consumption, medium acidification, and production of organic acids over time, besides increasing the of several phenolic compounds and antioxidant activity. Probiotic lactobacilli cultivated in fruit coproducts had increased survival percentages after freeze-drying and during 120 days of refrigerated storage. Moreover, probiotic lactobacilli cultivated and freeze-dried in fruit coproducts had larger subpopulations of live and metabolically active cells when exposed to simulated gastrointestinal digestion. The results showed that fruit coproducts not only improved the growth and helped to maintain the viability and metabolic activity of probiotic strains but also enriched the final fermented products with bioactive compounds, being an innovative circular strategy for producing high-quality probiotic cultures.

A unifying autocatalytic network-based framework for bacterial growth laws.

Recently discovered simple quantitative relations, known as bacterial growth laws, hint at the existence of simple underlying principles at the heart of bacterial growth. In this work, we provide a unifying picture of how these known relations, as well as relations that we derive, stem from a universal autocatalytic network common to all bacteria, facilitating balanced exponential growth of individual cells. We show that the core of the cellular autocatalytic network is the transcription-translation machinery-in itself an autocatalytic network comprising several coupled autocatalytic cycles, including the ribosome, RNA polymerase, and transfer RNA (tRNA) charging cycles. We derive two types of growth laws per autocatalytic cycle, one relating growth rate to the relative fraction of the catalyst and its catalysis rate and the other relating growth rate to all the time scales in the cycle. The structure of the autocatalytic network generates numerous regimes in state space, determined by the limiting components, while the number of growth laws can be much smaller. We also derive a growth law that accounts for the RNA polymerase autocatalytic cycle, which we use to explain how growth rate depends on the inducible expression of the rpoB and rpoC genes, which code for the RpoB and C protein subunits of RNA polymerase, and how the concentration of rifampicin, which targets RNA polymerase, affects growth rate without changing the RNA-to-protein ratio. We derive growth laws for tRNA synthesis and charging and predict how growth rate depends on temperature, perturbation to ribosome assembly, and membrane synthesis.

Studying the viability and growth kinetics of vancomycin-resistant Enterococcus faecalis V583 following femtosecond laser irradiation (420-465 nm).

Enterococcus faecalis is among the most resistant bacteria found in infected root canals. The demand for cutting-edge disinfection methods has rekindled research on photoinactivation with visible light. This study investigated the bactericidal activity of femtosecond laser irradiation against vancomycin-resistant Enterococcus faecalis V583 (VRE). The effect of parameters such as wavelength and energy density on the viability and growth kinetics of VRE was studied to design an optimized laser-based antimicrobial photoinactivation approach without any prior addition of exogenous photosensitizers. The most effective wavelengths were 430 nm and 435 nm at a fluence of 1000 J/cm2, causing a nearly 2-log reduction (98.6% and 98.3% inhibition, respectively) in viable bacterial counts. The colony-forming units and growth rate of the laser-treated cultures were progressively decreased as energy density or light dose increased at 445 nm but reached a limit at 1250 J/cm2. At a higher fluence of 2000 J/cm2, the efficacy was reduced due to a photobleaching phenomenon. Our results highlight the importance of optimizing laser exposure parameters, such as wavelength and fluence, in bacterial photoinactivation experiments. To our knowledge, this is the first study to report an optimized wavelength for the inactivation of VRE using visible femtosecond laser light.

Distinct Growth Responses of Tundra Soil Bacteria to Short-Term and Long-Term Warming.

Increases in Arctic temperatures have thawed permafrost and accelerated tundra soil microbial activity, releasing greenhouse gases that amplify climate warming. Warming over time has also accelerated shrub encroachment in the tundra, altering plant input abundance and quality, and causing further changes to soil microbial processes. To better understand the effects of increased temperature and the accumulated effects of climate change on soil bacterial activity, we quantified the growth responses of individual bacterial taxa to short-term warming (3 months) and long-term warming (29 years) in moist acidic tussock tundra. Intact soil was assayed in the field for 30 days using 18O-labeled water, from which taxon-specific rates of 18O incorporation into DNA were estimated as a proxy for growth. Experimental treatments warmed the soil by approximately 1.5°C. Short-term warming increased average relative growth rates across the assemblage by 36%, and this increase was attributable to emergent growing taxa not detected in other treatments that doubled the diversity of growing bacteria. However, long-term warming increased average relative growth rates by 151%, and this was largely attributable to taxa that co-occurred in the ambient temperature controls. There was also coherence in relative growth rates within broad taxonomic levels with orders tending to have similar growth rates in all treatments. Growth responses tended to be neutral in short-term warming and positive in long-term warming for most taxa and phylogenetic groups co-occurring across treatments regardless of phylogeny. Taken together, growing bacteria responded distinctly to short-term and long-term warming, and taxa growing in each treatment exhibited deep phylogenetic organization. IMPORTANCE Soil carbon stocks in the tundra and underlying permafrost have become increasingly vulnerable to microbial decomposition due to climate change. The microbial responses to Arctic warming must be understood in order to predict the effects of future microbial activity on carbon balance in a warming Arctic. In response to our warming treatments, tundra soil bacteria grew faster, consistent with increased rates of decomposition and carbon flux to the atmosphere. Our findings suggest that bacterial growth rates may continue to increase in the coming decades as faster growth is driven by the accumulated effects of long-term warming. Observed phylogenetic organization of bacterial growth rates may also permit taxonomy-based predictions of bacterial responses to climate change and inclusion into ecosystem models.

Propionic and valproic acids have an impact on bacteria viability, proton flux and ATPase activity.

Short-chain fatty acids like propionic (PPA) and valproic acids (VP) can alter gut microbiota, which is suggested to play a role in development of autism spectrum disorders (ASD). In this study we investigated the role of various concentrations of PPA and VP in gut enteric gram-negative Escherichia coli K12 and gram-positive Enterococcus hirae ATCC 9790 bacteria growth properties, ATPase activity and proton flux. The specific growth rate (µ) was 0.24 h-1 and 0.82 h-1 in E. coli and E. hirae, respectively. Different concentrations of PPA reduced the value of µ similarly in both strains. PPA affects membrane permeability only in E. hirae. PPA decreased DCCD-sensitive ATPase activity in the presence of K+ ions by 20% in E. coli and 40% in E. hirae suggesting the importance of the FOF1-K+ transport system in the regulation of PPA-disrupted homeostasis. Moreover, the H+ flux during PPA consumption could be the protective mechanism for enteric bacteria. VP has a selective effect on the µ depending on bacteria. The overwhelming effect of VP was detected on the K+-promoted ATPase activity in E. hirae. Taken together it can be suggested that PPA and VP have a disruptive effect on E. coli and E. hirae growth, viability, bioenergetic and biochemical properties, which are connected with the alteration of FOF1-ATPase activity and H+ flux rate or direction.