Concentration Of Broth Research Articles

Improved production of poly(γ‐glutamic acid) by Bacillus subtilisRKY3 and its recovery from viscous fermentation broth as a biodegradable polymer

AbstractBACKGROUNDPhysiological parameters (culture pH, aeration rate, and agitation speed) were optimized to improve γ‐PGA production by batch culture of Bacillus subtilis RKY3. The optimum conditions for recovery of γ‐PGA from highly viscous culture broth were also investigated.RESULTSEnhanced γ‐PGA production (41.4 g L−1, 397 cP) was observed under optimized physiological culture parameters (no pH control, 1.5 L min−1 aeration, and 300 rpm agitation). The cells were completely removed by diluting the viscous culture broth 7.5‐, 5.0‐, and 2.5‐fold at pH 6.0, 4.0, and 2.0, respectively. Maximum recovery of γ‐PGA was observed when the volume ratio of cell‐free culture broth to cold ethanol was 1:5 at pH 6.0. γ‐PGA with a molecular weight <100 kDa was successfully excluded in an ultrafiltration system to develop more economical recovery of γ‐PGA from cell‐free culture broth, which resulted in efficient γ‐PGA concentration with a molecular weight >100 kDa.CONCLUSIONThe physiological parameters affecting γ‐PGA production were optimized, and the isolation and recovery of γ‐PGA from viscous culture broth was also evaluated. Cells were removed completely by diluting the culture broth, and precipitation of γ‐PGA using cold ethanol was better than that of other alcohols. Ultrafiltration was found to be an efficient recovery method for concentration of culture broth containing γ‐PGA. © 2013 Society of Chemical Industry

Simultaneous saccharification and co-fermentation of whole wheat in integrated ethanol production

Two of the most important ways of reducing the production cost of lignocellulosic ethanol are to increase the ethanol yield and the concentration in the fermentation broth. This can be facilitated by co-fermentation of glucose and xylose from agricultural residues such as wheat straw, due to the high amount of xylose in the hemicelluloses in these materials.Simultaneous saccharification and co-fermentation (SSCF) of steam-pretreated wheat straw (SPWS) with and without the addition of liquefied wheat meal (LWM) was performed using the pentose-fermenting yeast, TMB3400. The highest overall ethanol yield in batch operation, of around 70%, equivalent to an ethanol concentration of 43.7 g L−1, was achieved using SPWS with 7.5% water-insoluble solids (WIS) and addition of LWM with 1% WIS. Using SPWS with a higher WIS (10%) resulted in a decreased yield, 60%, although the concentration of ethanol increased to 53.0 g L−1. SSCF of 7.5% straw was also performed with a single (after 20 h) or fed-batch addition of 1% WIS LWM (after 20, 24 and 28 h) resulting in an increase in both ethanol yield and concentration compared to the reference, without wheat meal addition, but no significant difference compared to the batch experiments.The addition of wheat meal to SSCF did not improve xylose utilization significantly, probably due to the instant release of glucose from the liquefied meal, which hampers the uptake of xylose. The instant release of glucose was shown to be caused by the high amylase activity of the β-glucosidase enzyme preparation.

Production of GABA (gamma amino butyric acid) by Lactic Acid Bacteria

Gamma-amino butyric acid (GABA) is a kind of pharmacological and biological component and its application is wide and useful in Korea specially, becoming aging society in the near feature. GABA is request special dose for the purposed biological effect but the production of concentrated GABA is very difficult due to low concentration of glutamic acid existed in the fermentation broth. To increase GABA concentrate using fermentation technology, high content of glutamic acid is required. For this reason, various strains which have the glutamic acid decarboxylase (GAD) and can convert glutamic acid to GABA, were isolated from various fermented foods. Most of GABA producing strains are lactic acid bacteria isolated from kimchi, especially added monosodium glutamate (MSG) as a taste enhancer. Optimizing the formulation of culture media and the culture condition, GABA conversion yield and amounts were increased. Finally GABA concentration of fermentation broth in batch or fed batch fermentation reached 660 mM or 1000 mM, respectively. Furthermore formulation of culture media for GABA production developed commercially. Many studies about GABA-rich product have been continued, so GABA-rich kimchi, cheese, yogurt, black raspberry juice and tomato juices has been also developed. In Korea many biological effects of GABA are evaluated recently and GABA will be expected to be used in multipurpose.

Fermentation of non-sterilized fish biomass with a mixed culture of film-forming yeasts and lactobacilli and its effect on innate and adaptive immunity in mice

Non-sterilized fish waste containing fish bones was fermented using combined starter cultures of film-forming yeast (Candida ethanolica) and lactic acid bacteria (LAB; Lactobacillus casei and Lactobacillus rhamnosus) in order to obtain a liquefied fermented broth without spoiling. During the entire fermentation, the number of LAB cells was maintained at a high level (6 × 10(8)-5 × 10(7) cells/ml). Although the number of general bacteria was 10(6)cell/ml after adding non-sterilized fish biomass, its growth was suppressed to be 1-3 × 10(4) cells/ml. The entire biomass had completely liquefied and the fermented broth contained all 20 α-amino acids composed of protein and also various kinds of minerals in abundance. The weight of mice group fed the fermented broth content feed (sample feed) for 31 days significantly increased compared with that fed no broth feed (control feed) (21.37 g vs 20.76 g (p < 0.05). No abnormal behavior and appearance were observed. All internal organs (the heart, the liver, the lung, the intestines, and the spleen) of both groups were confirmed to be normal by visual observation. In peripheral blood, the percentages of NK cells and CD8+ T cells of the mice in the sample feed group increased significantly relative to those in the control feed group (NK cells: 19% vs 11%, CD8+ T cells: 9% vs 5%, p < 0.05). In the spleen, the percentage of NK cells in the sample feed group also increased significantly compared to that in the control feed group (p < 0.05). The fermented fish biomass is expected to be effective for innate and adaptive immunity and thus fit for animal feed.

Using a two species competitive binding model to predict expanded bed breakthrough of a recombinant protein expressed in a high cell density fermentation

Expanded Bed experiments were conducted using a mixed mode (MM) resin to capture and purify a recombinant protein produced in yeast fermentation. Expanded bed breakthrough profiles show an overshoot in column effluent concentration of the target protein in the presence of cells and other broth proteins, similar to that seen by other researchers when loading two competing species onto packed beds. In this research, a numerical model assuming negligible axial dispersion is developed and first validated for columns loads that contain only the target protein. This model is solved by finite differences in a unique way that uses an embedded analytical-solution to increase solution speed and stability. To model expanded bed breakthrough of the target protein in the actual cell broth, it was assumed that the other non-product proteins in the broth compete for MM resin binding sites and might be represented as a second “average” species via a traditional two-component competitive Langmuir isotherm. Estimates of the Langmuir constant and broth concentration of this second species were then calculated from batch adsorption data. Using these parameters for the second species, and other batch-derived parameters for the target protein with this resin, this unique numerical modeling approach provided results that compare favorably to experimental breakthrough data at various flow rates. Finally, the model was employed for a parameter sensitivity analysis that shows which process variables are most important in determining breakthrough time and the shape and magnitude of the concentration overshoot.

Cyanobactericidal Effect of Streptomyces sp. HJC-D1 on Microcystis auruginosa

An isolated strain Streptomyces sp. HJC-D1 was applied to inhibit the growth of cyanobacterium Microcystis aeruginosa FACHB-905. The effect of Streptomyces sp. HJC-D1 culture broth on the cell integrity and physiological characteristics of M. aeruginosa FACHB-905 was investigated using the flow cytometry (FCM), enzyme activity and transmission electron microscopy (TEM) methods. Results showed that the growth of M. aeruginosa FACHB-905 was significantly inhibited, and the percentage of live cells depended on the culture broth concentration and exposure time. The activities of antioxidant enzymes including superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) increased with exposure concentration and exposure time, and the significant increase of reactive oxygen species (ROS) led to the disruption of the subcellular structure of M. aeruginosa FACHB-905, and caused the increase of malondialdehyde (MDA). Furthermore, TEM observation suggested the presence of three stages (cell breakage, organelle release and cell death) for the cyanobactericidal process of Streptomyces sp. HJC-D1. Therefore, Streptomyces sp. HJC-D1 not only affected antioxidant enzyme activities and ROS level, but also destroyed the subcellular structure of M. aeruginosa FACHB-905, demonstrating excellent cyanobactericidal properties.

Effects of Aliphatic Aldehydes on the Growth and Patulin Production ofPenicillium expansumin Apple Juice

The effects of 16 aliphatic aldehydes with 3-10 carbons on the growth and patulin production of Penicillium expansum were examined. When P. expansum spores were inoculated into apple juice broth, some alkenals, including 2-propenal, (E)-2-butenal, (E)-2-pentenal, and (E)-2-hexenal, inhibited fungal growth and patulin production. Their minimal inhibitory concentrations were 5, 50, 80, and 80 µg/mL respectively. Vital staining indicated that these alkenals killed mycelia within 4 h. Treatment of the spores with these aldehydes also resulted in rapid loss of germination ability, within 0.5-2 d. On the other hand, aliphatic aldehydes with 8-10 carbons significantly enhanced patulin production without affecting fungal growth: 300 µg/mL of octanal and 100 µg/mL of (E)-2-octenal increased the patulin concentrations in the culture broth by as much as 8.6- and 7.8-fold as compared to that of the control culture respectively. The expression of the genes involved in patulin biosynthesis in P. expansum was investigated in mycelia cultured in apple juice broth containing 300 µg/mL of octanal for 3.5, 5, and 7 d. Transcription of the msas gene, encoding 6-methylsalicylic acid synthase, which catalyzed the first step in the patulin biosynthetic pathway was remarkably high in the 3.5-d and 5-d-old cultures as compared with the control. However, octanal did not any increase the transcription of the msas in the 7-d-old culture or that of the other two genes, IDH and the peab1, in culture. Thus the enhanced patulin accumulation with supplementation with these aldehydes is attributable to the increased amount of the msas transcript.

Yeast biomass production: a new approach in glucose-limited feeding strategy

The aim of this work was to implement experimentally a simple glucose-limited feeding strategy for yeast biomass production in a bubble column reactor based on a spreadsheet simulator suitable for industrial application. In biomass production process using Saccharomyces cerevisiae strains, one of the constraints is the strong tendency of these species to metabolize sugars anaerobically due to catabolite repression, leading to low values of biomass yield on substrate. The usual strategy to control this metabolic tendency is the use of a fed-batch process in which where the sugar source is fed incrementally and total sugar concentration in broth is maintained below a determined value. The simulator presented in this work was developed to control molasses feeding on the basis of a simple theoretical model in which has taken into account the nutritional growth needs of yeast cell and two input data: the theoretical specific growth rate and initial cell biomass. In experimental assay, a commercial baker’s yeast strain and molasses as sugar source were used. Experimental results showed an overall biomass yield on substrate of 0.33, a biomass increase of 6.4 fold and a specific growth rate of 0.165 h−1 in contrast to the predicted value of 0.180 h-1 in the second stage simulation.

Improved efficiency of butanol production by absorbent fermentation with a renewable carrier

BackgroundBiobutanol production is still not economically competitive because of some principal drawbacks including high cost in feedstock consumption, low butanol concentration in the fermentation broth caused by severe product inhibition. An alternative fermentation mode is becoming an urgent requirement to solve these problems. Biobutanol production by absorbent fermentation with a renewable carrier, i.e. pretreated straw materials, is studied in this paper.ResultsCompared with other types of porous media, alkali-treated steam-exploded straw was proved to be a suitable carrier for absorbent fermentation of butanol. The Acetone-Butanol-Ethanol (ABE) concentration increased by 52% compared with submerged culture at an initial glucose concentration of 65 g/L. The adsorption of ABE solvent on substrate and increased bacterial concentration alleviated the end product inhibition and partly explained this positive effect. The steam pretreatment conditions, solid–liquid ratio, substrate types and substrate concentration were also investigated. Steam-explosion at 1.1 MPa for 4 min and solid–liquid ratio of 1:10 was shown to be the optimum. Glucose showed a great advantage over xylose, and higher glucose content was more conducive to biobutanol production. However, the yield of solvent decreased with the increased initial sugar concentration. Considering comprehensively, 100 g/L initial glucose was considered to be the optimum.ConclusionsThis work demonstrated an effective approach of improved butanol fermentation and its probable mechanisms of this positive effect, i.e. the adsorption of ABE solvent and the adhesion of bacteria on porous substrate accounted for the production improvement and the proportional variation of solvent constituents.

Structure Analysis of Microbe-Repaired Concrete Using Scanning Electron Micrographs

As one of the most popular materials used in construction, concrete is prone to superficial flaws, such as crack, due to the load-bearing and external environment. This research manually made cracks of 2 mm with 100 mm length and 30 mm depth on concrete vessels as specimens. Subsequently, bacteria, specifically B. pasteurii, was used in crack rehabilitation to enhance the compression strength of the repaired concrete. The mixture of microbes, urea medium, and urea-CaCl2 medium was added to a sludge and fine aggregate with a weight ratio of 0.6:1:1 to be the repairing material for crack rehabilitation. Crack rehabilitation was conducted by injected the mixture into the test samples after 90 days curing in saturated lime solution. In addition to the traditional test – compression test, scanning electron microscope (SEM) was used to examine the structure composition of the microbe-repaired concrete for calcium carbonate crystal formation. Various rectangular and polygonal crystals were observed in the SEM photographs of the microbe-repaired concrete samples with high bacterial concentrations demonstrated that bacteria can induce calcium carbonate precipitation to complete crack rehabilitation. The results prove that high concentration of bacterial broth induced a great amount of calcium carbonate precipitate and improved the concrete strength of the microbe-repaired samples.

Surface enhanced Raman scattering, antibacterial and antifungal active triangular gold nanoparticles

Shape controlled syntheses of gold nanoparticles have attracted a great deal of attention as their optical, electronic, magnetic and biological properties are strongly dependent on the size and shape of the particles. Here is a report on the surface enhanced Raman scattering (SERS) activity of Cinnamomum zeylanicum leaf broth reduced gold nanoparticles consisting of triangular and spherical like particles, using 2-aminothiophenol (2-ATP) and crystal violet (CV) as probe molecules. Nanoparticles prepared with a minimum leaf broth concentration, having a greater number of triangular like particles exhibit a SERS activity of the order of 107. The synthesized nanoparticles exhibit efficient antibacterial activity against the tested gram negative bacterium Escherichia coli and gram positive bacterium Staphylococcus aureus. Investigations on the antifungal activity of the synthesized nanoparticles against Aspergillus niger and Fusarium oxysporum positive is also discussed.

The chemical cleaning of ceramic membrane used in UF

Ultrafiltration (UF) is one of the membrane processes which is mostly used in the dairy industry for the separation and concentration of whey components or fermentation broth. Fouling of UF membranes in the food industry is primarily due to a deposition of microorganisms, proteins, fats and minerals on the membrane surface. Thus, cleaning of the membranes is an essential step of UF separation. The results from investigations of chemical cleaning of a ceramic UF membrane fouled by precipitation of whey components and yeast contained in the fermentation broth are presented. The effect of cleaning procedure on the degree of permeability restoration by the fouled membrane was studied. The results demonstrated that a combination of sodium hydroxide, phosphoric acid and sodium hypochlorite as a disinfectant could be successfully used to achieve an optimum recovery of the membrane properties.

Comparison of adsorption equilibrium and kinetic models for a case study of pharmaceutical active ingredient adsorption from fermentation broths: parameter determination, simulation, sensitivity analysis and optimization

Mathematical models for a batch process were developed to predict concentration distributions for an active ingredient (vancomycin) adsorption on a representative hydrophobic-molecule adsorbent, using differently diluted crude fermentation broth with cells as the feedstock. The kinetic parameters were estimated using the maximization of the coefficient of determination by a heuristic algorithm. The parameters were estimated for each fermentation broth concentration using four concentration distributions at initial vancomycin concentrations of 4.96, 1.17, 2.78, and 5.54 g l−¹. In sequence, the models and their parameters were validated for fermentation broth concentrations of 0, 20, 50, and 100% (v/v) by calculating the coefficient of determination for each concentration distribution at the corresponding initial concentration. The applicability of the validated models for process optimization was investigated by using the models as process simulators to optimize the two process efficiencies.

Simultaneous clostridial fermentation, lipase‐catalyzed esterification, and ester extraction to enrich diesel with butyl butyrate

The recovery of 1-butanol from fermentation broth is energy-intensive since typical concentrations in fermentation broth are below 20 g L(-1). To prevent butanol inhibition and high downstream processing costs, we aimed at producing butyl esters instead of 1-butanol. It is shown that it is possible to perform simultaneously clostridial fermentation, esterification of the formed butanol to butyl butyrate, and extraction of this ester by hexadecane. The very high partition coefficient of butyl butyrate pulls the esterification towards the product side even at fermentation pH and relatively low butanol concentrations. The hexadecane extractant is a model diesel compound and is nontoxic to the cells. If butyl butyrate enriched diesel can directly be used as car fuel, no product recovery is required. A proof-of-principle experiment for the one-pot bio-ester production from glucose led to 5 g L(-1) butyl butyrate in the hexadecane phase. The principle may be extended to a wide range of esters, especially to longer chain ones.

Reduction of Listeria monocytogenes in Raw Catfish Fillets by Essential Oils and Phenolic Constituent Carvacrol

The antimicrobial activity of various essential oils and carvacrol was determined on fresh raw catfish fillets against a 4-strain Listeria monocytogenes mixture representing serotypes 1/2b, 3b, 4b, and 4c that were predominantly isolated from catfish processing environments. Thyme oil, oregano oil and carvacrol exhibited concentration and time dependent responses in broth against L. monocytogenes; for example 0.5% concentrations resulted in 4 log CFU/mL reduction within 30 min whereas 0.1% concentrations required more than 24 h for the same level of reduction. Lemon, orange, and tangerine oils, at 0.5% showed listeriostatic effect in which 4 log CFU/mL of the initial L. monocytogenes load was unchanged at 4 °C in 10 d whereas 1% concentrations were listericidal in a time dependent manner. Apart from carvacrol, efficacy of tested essential oils in reducing L. monocytogenes and total microbial load from catfish fillet was very limited. Dipping treatment of catfish fillets in 2% carvacrol solution for 30 min at 4 °C reduced L. monocytogenes to an undetectable level from their initial load of 5 log CFU/g and reduced total microbial load from catfish fillets by approximately 5 log CFU/g. In sensory analysis trained panelist preferred control samples over 2% carvacrol treated samples implying potential limitation in applicability of carvacrol for fillet treatments.

Fuel ethanol production fromEucalyptus globuluswood by autocatalized organosolv pretreatment ethanol–water and SSF

AbstractBACKGROUNDLignocellulosic biomass (LCB) offers the only sustainable alternative to the use of fossil fuels as oil by employing its main components (cellulose, hemicellulose and lignin) as a carbon source for the production of biofuels, energy and value‐added chemicals. The aim of the present study was to investigate ethanol production from organosolv pretreatedEucalyptus globuluswood, carrying out the simultaneous sacharification and fermentation (SSF) process at a substrate loading of 10 and 15% (w/v) and using concentrations of 6 and 12 g L−1of the thermally acclimatizedS. cerevisiaeIR2T9‐a strain. These SSF experiments were also evaluated by increasing the enzyme loading in the reaction medium. Finally, a comparison was made between separate hydrolysis and fermentation (SHF) and SSF processes. With the information obtained and from published information, a general mass balance was developed.RESULTSThe highest ethanol concentration (∼42 g L−1) in the fermentation broth was obtained at a substrate consistency of 15% (w/v), enzyme loading of 20 FPU cellulase 40 UI β‐glucosidase g−1of pretreated material and using bothS. cerevisiaestrain IR2‐9a concentrations (6 and 12 g L−1).CONCLUSIONThe results of enzymatic hydrolysis (EH) show that increasing substrate content from 10 to 15% (w/v) decreases the conversion efficiency of cellulose to glucose. Furthermore, the mass balances of the process indicate that the SSF process is a better alternative than the SHF configuration, because larger amounts of ethanol can be obtained. Copyright © 2012 Society of Chemical Industry

Selective production of acetone during continuous synthesis gas fermentation by engineered biocatalyst Clostridium sp. MAceT113

To engineer acetogen biocatalyst capable of fermenting synthesis gas blend to acetone as the only liquid carbonaceous product. The metabolic engineering comprised inactivation of phosphotransacetylase via integration of a cassette comprising synthetic genes erm(B), thiolase and HMG-CoA synthase. Acetaldehyde dehydrogenase was inactivated via integration of a cassette consisting of synthetic genes cat, HMG-CoA lyase and acetoacetate decarboxylase. The engineered biocatalyst Clostridum sp. MAceT113 lost production of 253 mmol l(-1) ethanol and 296 mmol l(-1) acetate and started producing 1.8 mol l(-1) acetone in single-stage continuous syngas fermentation. The acetone concentration in culture broth is economical for bulk manufacture because it is about twenty times of that achieved with known acetone-butanol-ethanol fermentation of sugars. The process shows the opportunity to produce acetone from synthesis gas at concentrations comparable with production of acetone from products of petroleum cracking. This is the first report on elimination of acetate and acetaldehyde production and directing carbon flux from Acetyl-CoA to acetone via a non-naturally occurring in acetogen acetone biosynthesis pathway identified in eukaryotic organisms.

High‐titer n‐butanol production by clostridium acetobutylicum JB200 in fed‐batch fermentation with intermittent gas stripping

Acetone-butanol-ethanol (ABE) fermentation with a hyper-butanol producing Clostridium acetobutylicum JB200 was studied for its potential to produce a high titer of butanol that can be readily recovered with gas stripping. In batch fermentation without gas stripping, a final butanol concentration of 19.1 g/L was produced from 86.4 g/L glucose consumed in 78 h, and butanol productivity and yield were 0.24 g/L h and 0.21 g/g, respectively. In contrast, when gas stripping was applied intermittently in fed-batch fermentation, 172 g/L ABE (113.3 g/L butanol, 49.2 g/L acetone, 9.7 g/L ethanol) were produced from 474.9 g/L glucose in six feeding cycles over 326 h. The overall productivity and yield were 0.53 g/L h and 0.36 g/g for ABE and 0.35 g/L h and 0.24 g/g for butanol, respectively. The higher productivity was attributed to the reduced butanol concentration in the fermentation broth by gas stripping that alleviated butanol inhibition, whereas the increased butanol yield could be attributed to the reduced acids accumulation as most acids produced in acidogenesis were reassimilated by cells for ABE production. The intermittent gas stripping produced a highly concentrated condensate containing 195.9 g/L ABE or 150.5 g/L butanol that far exceeded butanol solubility in water. After liquid-liquid demixing or phase separation, a final product containing ~610 g/L butanol, ~40 g/L acetone, ~10 g/L ethanol, and no acids was obtained. Compared to conventional ABE fermentation, the fed-batch fermentation with intermittent gas stripping has the potential to reduce at least 90% of energy consumption and water usage in n-butanol production from glucose.

Biobutanol Recovery Using Nonfluorinated Task-Specific Ionic Liquids

Biobutanol has received major attention as an alternative for and additive to fossil fuels. Biobutanol produced via fermentation is hampered by low butanol concentrations in the fermentation broth. An efficient separation process is required to make biobutanol production economically viable. In this work, liquid–liquid extraction of butanol from water, employing nonfluorinated task-specific ionic liquids (TSILs) has been evaluated against distillation and extraction with conventional solvents. Experimental data for the equilibrium distribution ratios of butanol and water were used in a conceptual process design study to find the most promising solvent. The results show that the IL with the best distribution coefficient and very high selectivity was [TOAMNaph] (DBuOH = 21, S = 274), performing much better than the benchmark solvent oleyl alcohol (DBuOH = 3.42, S = 192). The conceptual design study showed that butanol extraction with [TOAMNaph] requires 73% less energy than in conventional distillation (5.65 MJ/kg BuOH vs 21.3 MJ/kg for distillation).

Modelling the liquid-water vein system within polar ice sheets as a potential microbial habitat

Based on the fundamental and distinctive physical properties of polycrystalline ice Ih, the chemical and temperature profiles within the polar ice sheets, and the observed selective partitioning of bacteria into liquid water filled veins in the ice, we consider the possibility that microbial life could survive and be sustained within glacial systems. Here, we present a set of modelled vertical profiles of vein diameter, vein chemical concentration, and vein water volume variability across a range of polar ice sheets using their ice core chemical profiles. A sensitivity analysis of VeinsInIce1.0, the numerical model used in this study shows that the ice grain size and the local borehole temperature are the most significant factors that influence the intergranular liquid vein size and the amount of freeze-concentrated impurities partitioned into the veins respectively. Model results estimate the concentration and characteristics of the chemical broth in the veins to be a potential extremophilic microbial medium. The vein sizes are estimated to vary between 0.3μm to 8μm across the vertical length of many polar ice sheets and they may contain up to 2μL of liquid water per litre of solid ice. The results suggest that these veins in polar ice sheets could accommodate populations of psychrophilic and hyperacidophilic ultra-small bacteria and in some regions even support the habitation of unicellular eukaryotes. This highlights the importance of understanding the potential impact of englacial microbial metabolism on polar ice core chemical profiles and provides a model for similar extreme habitats elsewhere in the universe.