Effect of moisture, temperature, and sulfur dioxide on color of dried apples

When sulfur dioxide is used in commercial drying of fruits in combination with low storage temperatures, browning and microbial spoilage can be inhibited. However, the relationship between moisture level, storage temperature, and sulfur dioxide content on the color of dried fruit is not known; therefore the purpose of this research was to determine the influence of temperature, sulfur dioxide content, and moisture level on the color of dried apples during storage. Dices (3/4" x 1/2" x 1/4") of Golden Delicious apples were dried after a 90 sec dip in aqueous solutions of 2500, 5000, or 7500 ppm of sulfur dioxide obtained from sodium bisulfite. The apples were dried to five different levels of moisture (13, 18, 22, 24, and 26% wet basis) and stored in controlled temperature rooms at 1°, 21°, and 38°C. Periodically the samples were analyzed for color (color index (CI) defined as Hunter L x a [subscript L] x b [subscript L]), total and free sulfur dioxide, moisture and water activity (a [subscript w]), to appreciate the changes of quality during 385 days of storage. Sulfur dioxide level was directly influenced by storage temperature. As temperature increased, the sulfur dioxide level in the dried apples decreased following a negative exponential curve. At 1°C nearly no variation in sulfur dioxide level was observed during the experiment. Loss of free sulfur dioxide followed the same pattern as total sulfur dioxide. The concentration of free sulfur dioxide was a larger proportion of the total as the concentration of total sulfur dioxide was increased. Moisture content of the dried apples decreased during storage at 38°C, but at 21°C moisture content decreased in the first 40 days reaching a level that remained constant until the end of the experiment. The constant level was approximately 85% of the initial moisture level. No appreciable change of water content occurred at 1°C. Water activities of the samples ranged between 0.40 and 0.85 and the optimal levels for color retention at the lower concentrations of total sulfur dioxide were approximately 0.75 a [subscript w]. This corresponded to a moisture of approximately 20%. Total sulfur dioxide, moisture and CI analysis of the dried apples were used to derive three equations, one for each temperature of storage. From these equations, the following relationships were evident. CI described the changes in color during the 385 days of the experiment. At 1°C sulfur dioxide and moisture influenced the changes of color approximately the same extent. Moisture content of 20% at all levels of sulfur dioxide at 1°C was optimal for maximum color preservation. Samples stored at 1°C retained an acceptable color longer than those stored at 21°C or 38°C. The approximation of the equation derived from regression analysis of the data of changes in color at 1°C was 63%. Changes in color at 21°C occurred faster than at 1°C. Acceptable colors were found until the 188 day samples. The water content of the samples had more influence on the color changes than the total sulfur dioxide content as determined by the regression equation. The regression equation describes 88% of the variations in color. Concentrations higher than 1500 ppm of total sulfur dioxide were necessary to maintain samples of acceptable colors for periods up to 188 days with moisture levels close to 20%. Storage temperature of 21°C was satisfactory for samples that do not require storage periods longer than 200 days and contain 1500 ppm of total sulfur dioxide and 20% moisture. Very rapid changes in the parameters studied were observed at 38°C. The samples were very dark after 40 days and none had an acceptable color after 101 days of storage. The regression equation derived from the data described 87% of the variations of color. The temperature of 38°C is not recommended under any condition for storage of dried apples. It was concluded that temperatures lower than 21°C and concentrations of approximately 1500 ppm of sulfur dioxide in the fruit tissue could preserve acceptable colors in samples of dried apples for periods of 200 days. Longer storage periods would be possible as temperature approaches 1°C. Using the equations obtained in this experiment, an estimation can be made of the storage life of dried apples. The response surface diagrams obtained are useful for visual comprehension of the influence of temperature, sulfur dioxide and moisture on color throughout the time of storage

Role of a Fur homolog in iron metabolism in Nitrosomonas europaea

<p>Abstract</p> <p>Background</p> <p>In response to environmental iron concentrations, many bacteria coordinately regulate transcription of genes involved in iron acquisition via the ferric uptake regulation (Fur) system. The genome of <it>Nitrosomonas europaea</it>, an ammonia-oxidizing bacterium, carries three genes (NE0616, NE0730 and NE1722) encoding proteins belonging to Fur family.</p> <p>Results</p> <p>Of the three <it>N. europaea fur </it>homologs, only the Fur homolog encoded by gene NE0616 complemented the <it>Escherichia coli </it>H1780 <it>fur </it>mutant. A <it>N. europaea fur:kanP </it>mutant strain was created by insertion of kanamycin-resistance cassette in the promoter region of NE0616 <it>fur </it>homolog. The total cellular iron contents of the <it>fur:kanP </it>mutant strain increased by 1.5-fold compared to wild type when grown in Fe-replete media. Relative to the wild type, the <it>fur:kanP </it>mutant exhibited increased sensitivity to iron at or above 500 μM concentrations. Unlike the wild type, the <it>fur:kanP </it>mutant was capable of utilizing iron-bound ferrioxamine without any lag phase and showed over expression of several outer membrane TonB-dependent receptor proteins irrespective of Fe availability.</p> <p>Conclusions</p> <p>Our studies have clearly indicated a role in Fe regulation by the Fur protein encoded by <it>N. europaea </it>NE0616 gene. Additional studies are required to fully delineate role of this <it>fur </it>homolog.</p

Steady-State Growth under Inorganic Carbon Limitation Conditions Increases Energy Consumption for Maintenance and Enhances Nitrous Oxide Production in Nitrosomonas europaea

Nitrosomonas europaea is a chemolithoautotrophic bacterium that oxidizes ammonia (NH₃) to obtain energy for growth on carbon dioxide (CO₂) and can also produce nitrous oxide (N₂O), a greenhouse gas. We interrogated the growth, physiological, and transcriptome responses of N. europaea to conditions of replete (>5.2 mM) and limited inorganic carbon (IC) provided by either 1.0 mM or 0.2 mM sodium carbonate (Na₂CO₃) supplemented with atmospheric CO₂. IC-limited cultures oxidized 25 to 58% of available NH₃ to nitrite, depending on the dilution rate and Na₂CO₃ concentration. IC limitation resulted in a 2.3-fold increase in cellular maintenance energy requirements compared to those for NH₃-limited cultures. Rates of N₂O production increased 2.5- and 6.3-fold under the two IC-limited conditions, increasing the percentage of oxidized NH₃-N that was transformed to N₂O-N from 0.5% (replete) up to 4.4% (0.2 mM Na₂CO₃). Transcriptome analysis showed differential expression (P ≤ 0.05) of 488 genes (20% of inventory) between replete and IC-limited conditions, but few differences were detected between the two IC-limiting treatments. IC-limited conditions resulted in a decreased expression of ammonium/ammonia transporter and ammonia monooxygenase subunits and increased the expression of genes involved in C₁ metabolism, including the genes for RuBisCO (cbb gene cluster), carbonic anhydrase, folate-linked metabolism of C₁ moieties, and putative C salvage due to oxygenase activity of RuBisCO. Increased expression of nitrite reductase (gene cluster NE0924 to NE0927) correlated with increased production of N₂O. Together, these data suggest that N. europaea adapts physiologically during IC-limited steady-state growth, which leads to the uncoupling of NH₃ oxidation from growth and increased N₂O production. IMPORTANCE: Nitrification, the aerobic oxidation of ammonia to nitrate via nitrite, is an important process in the global nitrogen cycle. This process is generally dependent on ammonia-oxidizing microorganisms and nitrite-oxidizing bacteria. Most nitrifiers are chemolithoautotrophs that fix inorganic carbon (CO₂) for growth. Here, we investigate how inorganic carbon limitation modifies the physiology and transcriptome of Nitrosomonas europaea, a model ammonia-oxidizing bacterium, and report on increased production of N₂O, a potent greenhouse gas. This study, along with previous work, suggests that inorganic carbon limitation may be an important factor in controlling N₂O emissions from nitrification in soils and wastewater treatment

Kinetic characterization of the soluble butane monooxygenase from Thauera butanivorans, formerly ‘Pseudomonas butanovora’

Soluble butane monooxygenase (sBMO), a three-component di-iron monooxygenase complex expressed by the C2–C9 alkane-utilizing bacterium Thauera butanivorans, was kinetically characterized by measuring substrate specificities for C1–C5 alkanes and product inhibition profiles. sBMO has high sequence homology with soluble methane monooxygenase (sMMO) and shares a similar substrate range, including gaseous and liquid alkanes, aromatics, alkenes and halogenated xenobiotics. Results indicated that butane was the preferred substrate (defined by kcat : Km ratios). Relative rates of oxidation for C1–C5 alkanes differed minimally, implying that substrate specificity is heavily influenced by differences in substrate Km values. The low micromolar Km for linear C2–C5 alkanes and the millimolar Km for methane demonstrate that sBMO is two to three orders of magnitude more specific for physiologically relevant substrates of T. butanivorans. Methanol, the product of methane oxidation and also a substrate itself, was found to have similar Km and kcat values to those of methane. This inability to kinetically discriminate between the C1 alkane and C1 alcohol is observed as a steady-state concentration of methanol during the two-step oxidation of methane to formaldehyde by sBMO. Unlike methanol, alcohols with chain length C2–C5 do not compete effectively with their respective alkane substrates. Results from product inhibition experiments suggest that the geometry of the active site is optimized for linear molecules four to five carbons in length and is influenced by the regulatory protein component B (butane monooxygenase regulatory component; BMOB). The data suggest that alkane oxidation by sBMO is highly specialized for the turnover of C3–C5 alkanes and the release of their respective alcohol products. Additionally, sBMO is particularly efficient at preventing methane oxidation during growth on linear alkanes ≥C2, despite its high sequence homology with sMMO. These results represent, to the best of our knowledge, the first kinetic in vitro characterization of the closest known homologue of sMM

Identifying Potential Mechanisms Enabling Acidophily in the Ammonia-Oxidizing Archaeon "Candidatus Nitrosotalea devanaterra"

Ammonia oxidation is the first and rate-limiting step in nitrification and is dominated by two distinct groups of microorganisms in soil: ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB). AOA are often more abundant than AOB and dominate activity in acid soils. The mechanism of ammonia oxidation under acidic conditions has been a long-standing paradox. While high rates of ammonia oxidation are frequently measured in acid soils, cultivated ammonia oxidizers grew only at near-neutral pH when grown in standard laboratory culture. Although a number of mechanisms have been demonstrated to enable neutrophilic AOB growth at low pH in the laboratory, these have not been demonstrated in soil, and the recent cultivation of the obligately acidophilic ammonia oxidizer “Candidatus Nitrosotalea devanaterra” provides a more parsimonious explanation for the observed high rates of activity. Analysis of the sequenced genome, transcriptional activity, and lipid content of “Ca. Nitrosotalea devanaterra” reveals that previously proposed mechanisms used by AOB for growth at low pH are not essential for archaeal ammonia oxidation in acidic environments. Instead, the genome indicates that “Ca. Nitrosotalea devanaterra” contains genes encoding both a predicted high-affinity substrate acquisition system and potential pH homeostasis mechanisms absent in neutrophilic AOA. Analysis of mRNA revealed that candidate genes encoding the proposed homeostasis mechanisms were all expressed during acidophilic growth, and lipid profiling by high-performance liquid chromatography–mass spectrometry (HPLC-MS) demonstrated that the membrane lipids of “Ca. Nitrosotalea devanaterra” were not dominated by crenarchaeol, as found in neutrophilic AOA. This study for the first time describes a genome of an obligately acidophilic ammonia oxidizer and identifies potential mechanisms enabling this unique phenotype for future biochemical characterization

Use of aliphatic n-alkynes to discriminate soil nitrification activities of ammonia-oxidizing thaumarchaea and bacteria

Ammonia (NH₃)-oxidizing bacteria (AOB) and thaumarchaea (AOA) co-occupy most soils, yet no short-term growth-independent method exists to determine their relative contributions to nitrification in situ. Microbial monooxygenases differ in their vulnerability to inactivation by aliphatic n-alkynes, and we found that NH₃ oxidation by the marine thaumarchaeon Nitrosopumilus maritimus was unaffected during a 24-h exposure to ≤20 μM concentrations of 1-alkynes C₈ and C₉. In contrast, NH₃ oxidation by two AOB (Nitrosomonas europaea and Nitrosospira multiformis) was quickly and irreversibly inactivated by 1 μM C₈ (octyne). Evidence that nitrification carried out by soilborne AOA was also insensitive to octyne was obtained. In incubations (21 or 28 days) of two different whole soils, both acetylene and octyne effectively prevented NH₄⁺-stimulated increases in AOB population densities, but octyne did not prevent increases in AOA population densities that were prevented by acetylene. Furthermore, octyne-resistant, NH₄⁺-stimulated net nitrification rates of 2 and 7 μg N/g soil/day persisted throughout the incubation of the two soils. Other evidence that octyne-resistant nitrification was due to AOA included (i) a positive correlation of octyne-resistant nitrification in soil slurries of cropped and noncropped soils with allylthiourea-resistant activity (100 μM) and (ii) the finding that the fraction of octyne-resistant nitrification in soil slurries correlated with the fraction of nitrification that recovered from irreversible acetylene inactivation in the presence of bacterial protein synthesis inhibitors and with the octyne-resistant fraction of NH₄⁺-saturated net nitrification measured in whole soils. Octyne can be useful in short-term assays to discriminate AOA and AOB contributions to soil nitrification.This is an author's peer-reviewed final manuscript, as accepted by the publisher. The published article is copyrighted by the American Society for Microbiology and can be found at: http://aem.asm.org/

Ca. Nitrososphaera and Bradyrhizobium are inversely correlated and related to agricultural practices in long-term field experiments

Agricultural land management, such as fertilization, liming, and tillage affects soil properties, including pH, organic matter content, nitrification rates, and the microbial community. Three different study sites were used to identify microorganisms that correlate with agricultural land use and to determine which factors regulate the relative abundance of the microbial signatures of the agricultural land-use. The three sites included in this study are the Broadbalk Experiment at Rothamsted Research, UK, the Everglades Agricultural Area, Florida, USA, and the Kellogg Biological Station, Michigan, USA. The effects of agricultural management on the abundance and diversity of bacteria and archaea were determined using high throughput, barcoded 16S rRNA sequencing. In addition, the relative abundance of these organisms was correlated with soil features. Two groups of microorganisms involved in nitrogen cycle were highly correlated with land use at all three sites. The ammonia oxidizing-archaea, dominated by Ca. Nitrososphaera, were positively correlated with agriculture while a ubiquitous group of soil bacteria closely related to the diazotrophic symbiont, Bradyrhizobium, was negatively correlated with agricultural management. Analysis of successional plots showed that the abundance of ammonia oxidizing-archaea declined and the abundance of bradyrhizobia increased with time away from agriculture. This observation suggests that the effect of agriculture on the relative abundance of these genera is reversible. Soil pH and NH(3) concentrations were positively correlated with archaeal abundance but negatively correlated with the abundance of Bradyrhizobium. The high correlations of Ca. Nitrososphaera and Bradyrhizobium abundances with agricultural management at three long-term experiments with different edaphoclimatic conditions allowed us to suggest these two genera as signature microorganisms for agricultural land use

Metabolic flexibility of enigmatic SAR 324 revealed through metagenomics and metatranscriptomics

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/102166/1/emi12165.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/102166/2/emi12165-sup-0001-figure.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/102166/3/emi12165-sup-0002-table.pd

Novel hydrocarbon monooxygenase genes in the metatranscriptome of a natural deep‐sea hydrocarbon plume

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/102241/1/emi12182.pd

Phylogenetic congruence and ecological coherence in terrestrial Thaumarchaeota

This work is licensed under a Creative Commons Attribution 4.0 International License. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in the credit line; if the material is not included under the Creative Commons license, users will need to obtain permission from the license holder to reproduce the material. Acknowledgements We would like to thank Dr Robert Griffith/CEH for providing DNA from soil samples and Dr Anthony Travis for his help with BioLinux. Sequencing was performed in NERC platform in Liverpool. CG-R was funded by a NERC fellowship NE/J019151/1. CQ was funded by a MRC fellowship (MR/M50161X/1) as part of the cloud infrastructure for microbial genomics consortium (MR/L015080/1).Peer reviewedPublisher PD