Alicyclobacillusspp. in the Fruit Juice Industry: History, Characteristics, and Current Isolation/Detection Procedures

Alicyclobacillus spp. in fruit-based products: Isolation, identification, quantitative assessment (SPME/GC-MS) of spoilage compounds and spore's resistance to thermal shocks

Alicyclobacillus spp. is the cause of great concern for the food industry due to their spores' resistance (thermal and chemical) and the spoilage potential of some species. Despite this, not all Alicyclobacillus strains can spoil fruit juices. Thus, this study aimed to identify Alicyclobacillus spp. strains isolated from fruit-based products produced in Argentina, Brazil, and Italy by DNA sequencing. All Alicyclobacillus isolates were tested for guaiacol production by the peroxidase method. Positive strains for guaiacol production were individually inoculated at concentration of 103 CFU/mL in 10 mL of orange (pH 3.90) and apple (pH 3.50) juices adjusted to 11°Brix, following incubation at 45 °C for at least 5 days to induce the production of the following spoilage compounds: Guaiacol, 2,6-dichlorophenol (2,6-DCP) and 2,6-dibromophenol (2,6-DBP). The techniques of micro-solid phase extraction by headspace (HS-SPME) and gas-chromatography with mass spectrometry (GC-MS) were used to identify and quantify the spoilage compounds. All GC-MS data was analyzed by principal component analysis (PCA). The effects of different thermal shock conditions on the recovery of Alicyclobacillus spores inoculated in orange and apple juice (11°Brix) were also tested. A total of 484 strains were isolated from 48 brands, and the species A. acidocaldarius and A. acidoterrestris were the most found among all samples analyzed. In some samples from Argentina, the species A. vulcanalis and A. mali were also identified. The incidence of these two main species of Alicyclobacillus in this study was mainly in products from pear (n = 108; 22.3 %), peach (n = 99; 20.5 %), apple (n = 86; 17.8 %), and tomato (n = 63; 13 %). The results indicated that from the total isolates from Argentina (n = 414), Brazil (n = 54) and Italy (n = 16) were able to produce guaiacol: 107 (25.8 %), 33 (61.1 %) and 13 (81.2 %) isolates from each country, respectively. The PCA score plot indicated that the Argentina and Brazil isolates correlate with higher production of guaiacol and 2,6-DCP/2,6-DBP, respectively. Heatmaps of cell survival after heat shock demonstrated that strains with different levels of guaiacol production present different resistances according to spoilage ability. None of the Alicyclobacillus isolates survived heat shocks at 120 °C for 3 min. This work provides insights into the incidence, spoilage potential, and thermal shock resistance of Alicyclobacillus strains isolated from fruit-based products.

Taxonomic Diversity and Functional Traits of Soil Bacterial Communities under Radioactive Contamination: A Review

Studies investigating the taxonomic diversity and structure of soil bacteria in areas with enhanced radioactive backgrounds have been ongoing for three decades. An analysis of data published from 1996 to 2024 reveals changes in the taxonomic structure of radioactively contaminated soils compared to the reference, showing that these changes are not exclusively dependent on contamination rates or pollutant compositions. High levels of radioactive exposure from external irradiation and a high radionuclide content lead to a decrease in the alpha diversity of soil bacterial communities, both in laboratory settings and environmental conditions. The effects of low or moderate exposure are not consistently pronounced or unidirectional. Functional differences among taxonomic groups that dominate in contaminated soil indicate a variety of adaptation strategies. Bacteria identified as multiple-stress tolerant; exhibiting tolerance to metals and antibiotics; producing antioxidant enzymes, low-molecular antioxidants, and radioprotectors; participating in redox reactions; and possessing thermophilic characteristics play a significant role. Changes in the taxonomic and functional structure, resulting from increased soil radionuclide content, are influenced by the combined effects of ionizing radiation, the chemical toxicity of radionuclides and co-contaminants, as well as the physical and chemical properties of the soil and the initial bacterial community composition. Currently, the quantification of the differential contributions of these factors based on the existing published studies presents a challenge.

Antibacterial effects of various molecular weight chitosans against Alicyclobacillus acidoterrestris in orange juice

Alicyclobacillus acidoterrestris has been gaining attention due to its unique thermo-acidophilic properties and being associated with the deterioration of pasteurized beverages. The objective of this study was to evaluate the antibacterial activity of chitosan with various molecular weights (MWs) (164, 85, 29.2, and 7.1 kDa) and concentrations (0-100 μg/mL) against A. acidoterrestris and its effect on guaiacol production. Various chitosan MWs were co-incubated for 7 days, and the bacterial growth, guaiacol, and vanillic acid contents during storage were determined. The chitosans performed antibacterial effects against A. acidoterrestris. Further, 164 kDa chitosan showed excellent results in controlling the growth and guaiacol formation in A. acidoterrestris. These findings demonstrated the efficacy of chitosan antibacterial activity against A. acidoterrestris and mitigating the guaiacol formation. Chitosan's antibacterial properties are attributed to the elimination of cells and suppression of guaiacol production. This study introduces a new approach for reducing A. acidoterrestris contamination in fruit juices, with potential product quality and safety advantages.

Inhibitory mechanism of quercetin on Alicyclobacillus acidoterrestris

In this the antibacterial of quercetin against Alicyclobacillus acidoterrestris was evaluated by measuring the minimal inhibitory concentration (MIC) and minimal bactericidal concentration (MBC). Subsequently, the effect of quercetin on A. acidoterrestris cell membrane was evaluated through scanning electron microscopy (SEM), surface hydrophobicity determination, diacetate fluorescein staining and propidium iodide (PI) staining. Additionally, the effects of quercetin on intracellular macromolecules and cell metabolism were explored by measuring the culture medium protein, bacterial protein and intracellular sodium and potassium adenosine triphosphate (ATP) enzyme activity. The results revealed that quercetin exhibited the MIC and MBC values of 100 ug/mL and 400 ug/mL, respectively, against A. acidoterrestris. The SEM results revealed that quercetin could induce irreversible damage to the cell membrane effectively. Moreover, quercetin could enhance the surface hydrophobicity of A. acidoterrestris. The results of flow cytometry and fluorescence microscopy analyses revealed that quercetin could promote cell damage by altering the cell membrane permeability of A. acidoterrestris, inducing the release of nucleic acid substances from the cells. Furthermore, the determination of protein content in the culture medium, bacterial protein content, and the Na(+)/K(+)-ATPase activity demonstrated that quercetin could reduce the intracellular protein content and impedes protein expression and ATPase synthesis effectively, leading to apoptosis.

Genomic insight and physiological characterization of thermoacidophilic Alicyclobacillus isolated from Yellowstone National Park

Introduction

Alicyclobacillus has been isolated from extreme environments such as hot springs, volcanoes, as well as pasteurized acidic beverages, because it can tolerate extreme temperatures and acidity. In our previous study, Alicyclobacillus was isolated during the enrichment of methane oxidizing bacteria from Yellowstone Hot Spring samples.

Methods

Physiological characterization and genomic exploration of two new Alicyclobacillus isolates, AL01A and AL05G, are the main focus of this study to identify their potential relationships with a thermoacidophilic methanotroph (Methylacidiphilum) isolated from the same hot spring sediments.

Results and discussion

In the present study, both Alicyclobacillus isolates showed optimal growth at pH 3.5 and 55°C, and contain ω-alicyclic fatty acids as a major lipid (ca. 60%) in the bacterial membrane. Genomic analysis of these strains revealed specific genes and pathways that the methanotroph genome does not have in the intermediary carbon metabolism pathway such as serC (phosphoserine aminotransferase), comA (phosphosulfolactate synthase), and DAK (glycerone kinase). Both Alicyclobacillus strains were also found to contain transporter systems for extracellular sulfate (ABC transporter), suggesting that they could play an important role in sulfur metabolism in this extreme environment. Genomic analysis of vitamin metabolism revealed Alicyclobacillus and Methylacidiphilum are able to complement each other's nutritional deficiencies, resulting in a mutually beneficial relationship, especially in vitamin B1(thiamin), B3 (niacin), and B7 (biotin) metabolism. These findings provide insights into the role of Alicyclobacillus isolates in geothermal environments and their unique metabolic adaptations to these environments.

Characterization and Genome Study of a Newly Isolated Temperate Phage Belonging to a New Genus Targeting Alicyclobacillus acidoterrestris

The spoilage of juices by Alicyclobacillus spp. remains a serious problem in industry and leads to economic losses. Compounds such as guaiacol and halophenols, which are produced by Alicyclobacillus, create undesirable flavors and odors and, thus, decrease the quality of juices. The inactivation of Alicyclobacillus spp. constitutes a challenge because it is resistant to environmental factors, such as high temperatures, and active acidity. However, the use of bacteriophages seems to be a promising approach. In this study, we aimed to isolate and comprehensively characterize a novel bacteriophage targeting Alicyclobacillus spp. The Alicyclobacillus phage strain KKP 3916 was isolated from orchard soil against the Alicyclobacillus acidoterrestris strain KKP 3133. The bacterial host's range and the effect of phage addition at different rates of multiplicity of infections (MOIs) on the host's growth kinetics were determined using a Bioscreen C Pro growth analyzer. The Alicyclobacillus phage strain KKP 3916, retained its activity in a wide range of temperatures (from 4 °C to 30 °C) and active acidity values (pH from 3 to 11). At 70 °C, the activity of the phage decreased by 99.9%. In turn, at 80 °C, no activity against the bacterial host was observed. Thirty minutes of exposure to UV reduced the activity of the phages by almost 99.99%. Based on transmission-electron microscopy (TEM) and whole-genome sequencing (WGS) analyses, the Alicyclobacillus phage strain KKP 3916 was classified as a tailed bacteriophage. The genomic sequencing revealed that the newly isolated phage had linear double-stranded DNA (dsDNA) with sizes of 120 bp and 131 bp and 40.3% G+C content. Of the 204 predicted proteins, 134 were of unknown function, while the remainder were annotated as structural, replication, and lysis proteins. No genes associated with antibiotic resistance were found in the genome of the newly isolated phage. However, several regions, including four associated with integration into the bacterial host genome and excisionase, were identified, which indicates the temperate (lysogenic) life cycle of the bacteriophage. Due to the risk of its potential involvement in horizontal gene transfer, this phage is not an appropriate candidate for further research on its use in food biocontrol. To the best of our knowledge, this is the first article on the isolation and whole-genome analysis of the Alicyclobacillus-specific phage.

Role and Mechanism of Cold Plasma in Inactivating Alicyclobacillus acidoterrestris in Apple Juice

A. acidoterrestris has been identified as the target bacterium in fruit juice production due to its high resistance to standard heat treatment. Multiple studies have shown that cold plasma can effectively inactivate pathogenic and spoilage microorganisms in juices. However, we are aware of only a few studies that have used cold plasma to inactivate A. acidoterrestris. In this study, the inactivation efficacy of cold plasma was determined using the plate count method and described using a biphasic model. The effects of the food matrix, input power, gas flow rate, and treatment time on inactivation efficacy were also discovered. Scavenging experiments with reactive oxygen species (•OH, •O2−, and 1O2), scanning electron microscopy (SEM), Raman spectra, as well as an in vitro toxicology assay kit, were used to determine the inactivation mechanism. According to the plate count method, a maximum reduction of 4.14 log CFU/ mL could be achieved within 7 s, and complete inactivation could be achieved within 240 s. The scavenging experiments showed that directly cold plasma-produced singlet oxygen plays the most crucial role in inactivation, which was also confirmed by the fluorescence probe SOSG. The scanning electron microscopy (SEM) and Raman spectra showed that the cold plasma treatment damaged the membrane integrity, DNA, proteins, lipids, and carbohydrates of A. acidoterrestris. The plate count results and the apple juice quality evaluation showed that the cold plasma treatment (1.32 kV) could inactivate 99% of A. acidoterrestris within 60 s, with no significant changes happening in apple juice quality, except for slight changes in the polyphenol content and color value.

Application and potential of multifrequency ultrasound in juice industry: Comprehensive analysis of inactivation and germination of Alicyclobacillus acidoterrestris spores

The majority of acidic fruits are perishable owing to their high-water activity, which promotes microbial activity, thus exhibiting metabolic functions that cause spoilage. Along with sanitary practices, several treatments are used during processing and/or storage to inhibit the development of undesirable bacteria. To overcome the challenges caused by mild heat treatment, juice manufacturers have recently increased their involvement in developing novel non-thermal processing procedures. Ultrasonication alone or in combination with other hurdle technologies may be used to pasteurize processed fruit juices. Multifrequency ultrasound has gained popularity due to the fact that mono-frequency ultrasound has less impact on bacterial inactivation and bioactive compound enhancement of fruit juice. Here, we present and discuss the fundamental information and technological knowledge of how spoilage bacteria, specifically Alicyclobacillus acidoterrestris, assemble resistant spores and inactivate and germinate dormant spores in response to nutrient germinants and physical treatments such as heat and ultrasound. To the authors' knowledge, no prior review of ultrasonic inactivation and germination of A. acidoterrestris in fruit juice exists. Therefore, this article aims to provide a review of previously published research on the inactivation and germination of A. acidoterrestris in fruit juice by ultrasound and heat.

Headspace control and antimicrobials: inhibition strategies to prevent growth of Alicyclobacillus acidoterrestris in orange juice

Alicyclobacillus acidoterrestris can cause spoilage in orange juice that leads to consumer rejection. Six different orange juices were physiochemically characterized (pH, total soluble solids, titratable acidity, total polyphenols and vitamin C). A bottle for each sampling point per juice was filled (headspace: 40% volume) and inoculated with 10² - 10³ CFU ml^-1 of A. acidoterrestris ATCC® 49025™ (heat shocked before inoculation: 75°C, 20 min). Samples were stored for 21 d at 45 ± 1°C and plate counted periodically on acidified YSG agar (pH 3.7) incubated at 45 ± 1°C for 3 d. The effect of headspace (6% versus 40% volume) on A. acidoterrestris growth was also evaluated. The effect of nisin (0.006%, 0.003%, 0.0015%, and 0.00075%), sodium benzoate (0.1%), potassium sorbate (0.1%), and a mix of benzoate and sorbate (0.05% each) on A. acidoterrestris was additionally addressed. A. acidoterrestris reached up to 10⁷ CFU ml^-1 in five of the six juices in less than one week. Headspace significantly impacted (P<0.05) A. acidoterrestris maximum population, which reached the critical value of 5 log CFU ml^-1 at 40% headspace. All preservatives, regardless of concentration, showed a bacteriostatic effect during 22 d of storage with no significant differences among treatments (P>0.05).

Fruit Juice Spoilage by Alicyclobacillus: Detection and Control Methods—A Comprehensive Review

Fruit juices have an important place in humans’ healthy diet. They are considered to be shelf stable products due to their low pH that prevents the growth of most bacteria. However thermo-acidophilic endospore forming bacteria of the genus Alicyclobacillus have the potential to cause spoilage of commercially pasteurized fruit juices. The flat sour type spoilage, with absence of gas production but presence of chemical spoilage compounds (mostly guaiacol) and the ability of Alicyclobacillus spores to survive after pasteurization and germinate under favorable conditions make them a major concern for the fruit juice industry worldwide. Their special characteristics and presence in the fruit juice industry has resulted in the development of many isolation and identification methods based on cell detection (plating methods, ELISA, flow cytometry), nucleic acid analysis (PCR, RAPD-PCR, ERIC-PCR, DGGE-PCR, RT-PCR, RFLP-PCR, IMS-PCR, qPCR, and 16S rRNA sequencing) and measurement of their metabolites (HPLC, GC, GC-MS, GC-O, GC-SPME, Electronic nose, and FTIR). Early detection is a big challenge that can reduce economic loss in the industry while the development of control methods targeting the inactivation of Alicyclobacillus is of paramount importance as well. This review includes a discussion of the various chemical (oxidants, natural compounds of microbial, animal and plant origin), physical (thermal pasteurization), and non-thermal (High Hydrostatic Pressure, High Pressure Homogenization, ultrasound, microwaves, UV-C light, irradiation, ohmic heating and Pulse Electric Field) treatments to control Alicyclobacillus growth in order to ensure the quality and the extended shelf life of fruit juices.

Lactic acid production from mesophilic and thermophilic fermentation of food waste at different pH

It is promising to recover lactic acid (LA) from fermentation of food waste (FW). In this study, pH and temperatures were investigated comprehensively to find their effects on LA fermentation, and microbial analyses were used to take insight to the variation of LA production. The results showed that mesophilic fermentation benefited hydrolysis and acidification, leading to a high yield of LA, while thermophilic conditions restricted other producers at low pH, leading to a high purity of LA. Lactobacillus amylolyticus was the main LA producer under thermophilic conditions, but Thermoanaerobacterium thermosaccharolyticum boomed at pH 5.0-6.0 and it converted LA partly to butyric acid. Simultaneously, Bacillus coagulans also increased and improved the optical purity (OP) of L-LA. From a series of this study, an operational condition of pH 5.5 and temperature of 52 °C would be potentially suitable for lactate fermentation of FW with high purity of 89%, while a stable LA production with an OP of 68% was achieved at 55 °C and pH 6.0.

Use of nanoencapsulated curcumin against vegetative cells and spores of Alicyclobacillus spp. in industrialized orange juice

Pathogenic and deteriorating bacteria are a great concern to food safety. In this sense, the present study evaluated the fight against microbial contamination through the use of nanoparticles containing curcumin, in addition to analyzing the physical properties of these nanoparticles. Efficient curcumin encapsulation was determined by Fourier transform infrared spectra evaluation and differential scanning calorimetry. Transmission electron microscopy images showed irregular shaped nanoparticles with broad size distribution (20-250 nm). The antibacterial activity was considered satisfactory, since curcumin in the form of nanoparticles demonstrated antimicrobial and antibacterial activity superior to curcumin in its free form, against both pathogenic bacteria, such as Staphylococcus aureus (MIC 125 μg/mL), and deteriorates, such as Alicyclobacillus acidoterrestris (MIC 62.5 μg/mL). Since curcumin nanoparticles may be consumed as a food additive, the bioactive properties of the nanoencapsulated curcumin were also evaluated in relation to antioxidant capacity (Thiobarbituric acid reactive substances (TBARS) and oxidative hemolysis inhibition assays) and cytotoxicity against four carcinoma cell lines, as well as two non-tumor cells. As a proof of concept, nanoparticles were incorporated in orange juice, with the juice maintaining satisfactory pH, °Brix, and color stability, during three days of storage (8 °C).

Bacterial Spore Inactivation in Orange Juice and Orange Peel by Ultraviolet-C Light

Spore-forming bacteria are a great concern for fruit juice processors as they can resist the thermal pasteurization and the high hydrostatic pressure treatments that fruit juices receive during their processing, thus reducing their microbiological quality and safety. In this context, our objective was to evaluate the efficacy of Ultraviolet-C (UV-C) light at 254 nm on reducing bacterial spores of Alicyclobacillus acidoterrestris, Bacillus coagulans and Bacillus cereus at two stages of orange juice production. To simulate fruit disinfection before processing, the orange peel was artificially inoculated with each of the bacterial spores and submitted to UV-C light (97.8-100.1 W/m²) with treatment times between 3 s and 10 min. The obtained product, the orange juice, was also tested by exposing the artificially inoculated juice to UV-C light (100.9-107.9 W/m²) between 5 and 60 min. A three-minute treatment (18.0 kJ/m²) reduced spore numbers on orange peel around 2 log units, while more than 45 min (278.8 kJ/m²) were needed to achieve the same reduction in orange juice for all evaluated bacterial spores. As raw fruits are the main source of bacterial spores in fruit juices, reducing bacterial spores on fruit peels could help fruit juice processors to enhance the microbiological quality and safety of fruit juices.

Characterization of a new electrochemically active bacterium phylogenetically related to Alicyclobacillus hesperidum and its electrochemical performance in microbial fuel cell

Extremophilic microorganisms in microbial electrochemical systems have opened new possibilities for waste treatment. Here, a phenomenon of electricity generation under acidophilic condition was found in organic acid fermentation wastewater treatment using microbial fuel cell (MFC). The anodic microbial community analysis showed that the percentage of Firmicutes was 99.03%, which accounted for the vast majority of the microbial community at the late discharge stage with pH 3.0. As the dominant bacterium of Firmicutes, Alicyclobacillus hesperidum EG was isolated and identified. MFC experiments confirmed that Alicyclobacillus hesperidum EG exhibited good electricity generating capability with a maximum power density of 188.1 mW m^-2 at 50 °C and low pH. It is the first time that Alicyclobacillus hesperidum EG was discovered as a newly electrochemically active bacterium. Additionally, the morphological analysis combined with electrochemical experiments demonstrated that no nanowires were found in the anodic biofilm of Alicyclobacillus hesperidum EG, and Alicyclobacillus hesperidum EG may produce soluble redox-active small molecules as electron shuttles to facilitate extracellular electron transfer. Based on unique characteristics such as good acid resistance, high temperature resistance, and high electricity generation ability, Alicyclobacillus hesperidum EG exhibited great potential in wastewater treatment and energy recovery.

Short Wave Ultraviolet Light (UV-C) Effectiveness in the Inactivation of Bacterial Spores Inoculated in Turbid Suspensions and in Cloudy Apple Juice

Liquid foods might present interferences in their optical properties that can reduce the effectiveness of short-wave ultraviolet radiation (UV-C) treatments used for sterilization purposes. The effect of turbidity as UV-C interference factor against the inactivation of bacterial spores was analysed by using phosphate-buffered saline solutions (PBS) of different turbidity values (2000, 2500, and 3000 NTU) which were adjusted with the addition of apple fibre. These suspensions were inoculated with spores of Bacillus subtilis and Alicyclobacillus acidoterrestris. While higher UV-C doses increased the inactivation rates of spores, these were reduced when turbidity values increased; a dose of 28.7 J/mL allowed inactivation rates of B. subtilis spores of 3.96 Log in a 2000-NTU suspension compared with 2.81 Log achieved in the 3000-NTU one. Spores of B. subtilis were more UV-C-resistant than A. acidoterrestris. Cloudy apple juice inoculated with A. acidoterrestris spores was processed by UV-C at different doses in a single pass and with recirculation of the matrix through the reactor. Inactivation increased significantly with recirculation, surpassing 5 Log after 125 J/mL compared with 0.13 Log inactivation after a single-pass treatment at the same UV-C dose. UV-C treatments with recirculation affected the optical properties (absorption coefficient at 254 nm and turbidity) of juice and increased browning as UV-C doses became higher.

Preparation of species-specific monoclonal antibody and development of fluorescence immunoassay based on fluorescence resonance energy transfer of carbon dots for accurate and sensitive detection of Alicyclobacillus acidoterrestris in apple juice

The growth and metabolism of Alicyclobacillus acidoterrestris can lead to the spoilage of commercial fruit juice. Existing methods have some drawbacks such as complex sample pretreatment, skilled technician requirement, reduced sensitivity and specificity. Herein, a novel fluorescence immunoassay was developed using a monoclonal antibody (mAb) against A. acidoterrestris as the sensing element and carbon dots (CDs) as the signal response unit. The CDs can be quenched via fluorescence resonance energy transfer (FRET) by the oxidization product of p-phenylenediamine (PPD), a chromogenic substrate of horseradish peroxidase (HRP). This approach showed enhanced accuracy and sensitivity with relatively low limit of detection (LOD) of 6.16 × 10² CFU mL^-1. Moreover, apple juice contaminated with 1 CFU mL^-1 of A. acidoterrestris can be identified after 24 h enrichment. This fluorescence immunoassay could serve as a powerful tool for laboratory identification and on-site inspection of A. acidoterrestris, reducing the adverse effect on the quality of fruit juice.

Metabolic extract of the endophytic fungus Flavodon flavus isolated from Justicia brandegeana in the control of Alicyclobacillus acidoterrestris in commercial orange juice

In this work, the antibacterial activity of a crude extract of the endophytic fungus Flavodon flavus (JB257), isolated from leaves of Justicia brandegeana, was evaluated against both the vegetative and sporulated forms of Alicyclobacillus acidoterrestris. The microdilution technique was performed in order to determine the antibacterial activity of the crude extract alone as well as in combination with the bacteriocin, nisin. The minimum inhibitory concentration (MIC) of the crude extract and nisin alone against A. acidoterrestris vegetative forms were 250 μg/mL and 31.5 μg/mL, respectively, while the minimum bactericidal concentrations (MBC) were 1000 μg/mL and 62.5 μg/mL,respectively. For A. acidoterrestris spores, treatment with the crude extract at a concentration of 500 μg/mL caused a 47% reduction in growth, while nisin at 62.5 μg/mL could reduce 100% of the growth. The in vitro evaluation of the crude extract combined with nisin against A. acidoterrestris by the Checkerboard method showed a synergistic interaction between the two compounds. In addition, greater selectivity towards bacterial cells over host cells, a human hepatocyte cell line, was achieved when the crude extract was combined with nisin, Using scanning electron microscopy, interferences in the cell membrane of A. acidoterrestris could be observed after treatment with the crude extract. The results presented in this study indicate that the crude extract of the endophyte F. flavus has biotechnological potential in the food industry, especially for the treatment of orange juices through the control of A. acidoterrestris.

Alicyclobacillus acidoterrestris Strain Variability in the Inactivation Kinetics of Spores in Orange Juice by Temperature-Assisted High Hydrostatic Pressure

In this work, the inactivation kinetics of Alicyclobacillus acidoterrestris spores by temperature-assisted high hydrostatic pressure was assessed by means of the Weibull model. Spores from two A. acidoterrestris strains (a wild-type strain and a reference strain) were inoculated in commercial orange juice and subjected to high pressure levels (500 and 600 MPa) combined with four temperature regimes (25, 45, 60 and 70 °C) for time up to 30 min. Results showed that for a given high-pressure level spore inactivation was higher as temperature progressively increased. Furthermore, the Weibull model consistently produced satisfactory fit to the inactivation data based on the values of the root mean squared error (RMSE < 0.54 log colony-forming units (CFU)/mL) and the coefficient of determination (R2 > 0.90 in most cases). The shape of inactivation curves was concave upward (p < 1) for all temperature/high pressure levels tested, indicating rapid inactivation of the sensitive cells of the bacterium whereas the remaining ones adapted to high hydrostatic pressure (HHP) treatment. The values of the shape (p) and scale (δ) parameters of the Weibull model were dependent on the applied temperature for a given high pressure level and they were further described in a secondary model using first-order fitting curves to provide predictions of the surviving spore population at 55 and 65 °C. Results revealed a systematic over-prediction for the wild-type strain regardless of temperature and high pressure applied, whereas for the reference strain under-prediction was evident after 3 log-cycles reduction of the surviving bacteria spores. Overall, the results obtained indicate that the effectiveness of high hydrostatic pressure against A. acidoterrestris spores is strain-dependent and also underline the need for temperature-assisted HPP for effective spore inactivation during orange juice processing.

Application of a Krypton-Chlorine Excilamp To Control Alicyclobacillus acidoterrestris Spores in Apple Juice and Identification of Its Sporicidal Mechanism

The aim of this study was to investigate the sporicidal effect of a krypton-chlorine (KrCl) excilamp against Alicyclobacillus acidoterrestris spores and to compare its inactivation mechanism to that of a conventional UV lamp containing mercury (Hg). The inactivation effect of the KrCl excilamp was not significantly different from that of the Hg UV lamp for A. acidoterrestris spores in apple juice despite the 222-nm wavelength of the KrCl excilamp having a higher absorption coefficient in apple juice than the 254-nm wavelength of the Hg UV lamp; this is because KrCl excilamps have a fundamentally greater inactivation effect than Hg UV lamps, which is confirmed under ideal conditions (phosphate-buffered saline). The inactivation mechanism analysis revealed that the DNA damage induced by the KrCl excilamp was not significantly different (P > 0.05) from that induced by the Hg UV lamp, while the KrCl excilamp caused significantly higher (P < 0.05) lipid peroxidation incidence and permeability change in the inner membrane of A. acidoterrestris spores than did the Hg UV lamp. Meanwhile, the KrCl excilamp did not generate significant (P > 0.05) intracellular reactive oxygen species, indicating that the KrCl excilamp causes damage only through the direct absorption of UV light. In addition, after KrCl excilamp treatment with a dose of 2,011 mJ/cm2 to reduce A. acidoterrestris spores in apple juice by 5 logs, there were no significant (P > 0.05) changes in quality parameters such as color (L*, a*, and b*), total phenolic compounds, and DPPH (2,2-diphenyl-1-picrylhydrazyl) free radical scavenging activity.IMPORTANCEAlicyclobacillus acidoterrestris spores, which have high resistance to thermal treatment and can germinate even at low pH, are very troublesome in the juice industry. UV technology, a nonthermal treatment, can be an excellent means to control heat-resistant A. acidoterrestris spores in place of thermal treatment. However, the traditionally applied UV sources are lamps that contain mercury (Hg), which is harmful to humans and the environment; thus, there is a need to apply novel UV technology without the use of Hg. In response to this issue, excilamps, an Hg-free UV source, have been actively studied. However, no studies have been conducted applying this technique to control A. acidoterrestris spores. Therefore, the results of this study, which applied a KrCl excilamp for the control of A. acidoterrestris spores and elucidated the inactivation principle, are expected to be utilized as important basic data for application to actual industry or conducting further studies.

Laboratory contamination over time during low-biomass sample analysis

Bacteria are not only ubiquitous on earth but can also be incredibly diverse within clean laboratories and reagents. The presence of both living and dead bacteria in laboratory environments and reagents is especially problematic when examining samples with low endogenous content (e.g., skin swabs, tissue biopsies, ice, water, degraded forensic samples or ancient material), where contaminants can outnumber endogenous microorganisms within samples. The contribution of contaminants within high‐throughput studies remains poorly understood because of the relatively low number of contaminant surveys. Here, we examined 144 negative control samples (extraction blank and no‐template amplification controls) collected in both typical molecular laboratories and an ultraclean ancient DNA laboratory over 5 years to characterize long‐term contaminant diversity. We additionally compared the contaminant content within a home‐made silica‐based extraction method, commonly used to analyse low endogenous content samples, with a widely used commercial DNA extraction kit. The contaminant taxonomic profile of the ultraclean ancient DNA laboratory was unique compared to modern molecular biology laboratories, and changed over time according to researcher, month and season. The commercial kit also contained higher microbial diversity and several human‐associated taxa in comparison to the home‐made silica extraction protocol. We recommend a minimum of two strategies to reduce the impacts of laboratory contaminants within low‐biomass metagenomic studies: (a) extraction blank controls should be included and sequenced with every batch of extractions and (b) the contributions of laboratory contamination should be assessed and reported in each high‐throughput metagenomic study.

Potential use of electronic tongue coupled with chemometrics analysis for early detection of the spoilage of Zygosaccharomyces rouxii in apple juice

Apple juice spoilage by Zygosaccharomyces rouxii could scarcely be identified at early stage. It is crucial to recognize the spoilage at early stage to prevent waste of products. In present study, electronic tongue was applied to detect the spoilage of Z. rouxii in apple juice, using taste evaluation by panelists as reference. Combined with linear discriminant analysis, identification of the contaminated juice was fulfilled after 12 h, equivalent to yeast population of less than 2.0 lg colony forming units/mL. At the level, panelists were not capable of discerning the spoilage. Sensors HA, ZZ, BB and BA were relatively more sensitive to the changes in overall taste of apple juice. Moreover, cell number of Z. rouxii could be properly quantified by partial least squares regression models with high determination coefficient of 0.98-0.99. Electronic tongue appears to be a powerful approach to realize early detection of contamination of Z. rouxii.

Surface Immunoproteomics Reveals Potential Biomarkers in Alicyclobacillus acidoterrestris

Alicyclobacillus acidoterrestris is a major putrefying bacterium that can cause pecuniary losses in the global juice industry. Current detection approaches are time-consuming and exhibit reduced specificity and sensitivity. In this study, an immunoproteomic approach was utilized to identify specific biomarkers from A. acidoterrestris for the development of new detection methods. Cell surface-associated proteins were extracted and separated by 2-D (two-dimensional) gel electrophoresis. Immunogenic proteins were detected by Western blot analysis using antisera against A. acidoterrestris. Twenty-two protein spots exhibiting immunogenicity were excised and eighteen of the associated spots were successfully identified by matrix-assisted laser desorption/ionization time-of-flight tandem mass spectrometry (MALDI-TOF/TOF MS). These proteins were observed to be involved in energy and carbohydrate metabolism, transmembrane transport, response to oxidative stress, polypeptide biosynthesis, and molecule binding activity. This is the first report detailing the identification of cell surface-associated antigens of A. acidoterrestris. The identified immunogenic proteins could serve as potential targets for the development of novel detection methods.

Microbial community composition of a hydrocarbon reservoir 40 years after a CO2 enhanced oil recovery flood

Injecting CO₂ into depleted oil reservoirs to extract additional crude oil is a common enhanced oil recovery (CO₂-EOR) technique. However, little is known about how in situ microbial communities may be impacted by CO₂ flooding, or if any permanent microbiological changes occur after flooding has ceased. Formation water was collected from an oil field that was flooded for CO₂-EOR in the 1980s, including samples from areas affected by or outside of the flood region, to determine the impacts of CO₂-EOR on reservoir microbial communities. Archaea, specifically methanogens, were more abundant than bacteria in all samples, while identified bacteria exhibited much greater diversity than the archaea. Microbial communities in CO₂-impacted and non-impacted samples did not significantly differ (ANOSIM: Statistic R = -0.2597, significance = 0.769). However, several low abundance bacteria were found to be significantly associated with the CO₂-affected group; very few of these species are known to metabolize CO₂ or are associated with CO₂-rich habitats. Although this study had limitations, on a broad scale, either the CO₂ flood did not impact the microbial community composition of the target formation, or microbial communities in affected wells may have reverted back to pre-injection conditions over the ca. 40 years since the CO₂-EOR.

Homogeneous Synthesis of Cationic Chitosan via New Avenue

Using a solvent formed of alkali and urea, chitosan was successfully dissolved in a new solvent via the freezing⁻thawing process. Subsequently, quaternized chitosan (QC) was synthesized using 3-chloro-2-hydroxypropyl trimethyl ammonium chloride (CHPTAC) as the cationic reagent under different incubation times and temperatures in a homogeneous system. QCs cannot be synthesized at temperatures above 60 °C, as gel formation will occur. The structure and properties of the prepared QC were characterized and quaternary groups were comfirmed to be successfully incorporated onto chitosan backbones. The degree of substitution (DS) ranged from 16.5% to 46.8% and the yields ranged from 32.6% to 89.7%, which can be adjusted by changing the molar ratio of the chitosan unit to CHPTAC and the reaction time. QCs inhibits the growth of Alicyclobacillus acidoterrestris effectively. Thus, this work offers a simple and green method of functionalizing chitosan and producing quaternized chitosan with an antibacterial effect for potential applications in the food industry.

Microbial communities and their predicted metabolic functions in a desiccating acid salt lake

The waters of Lake Magic in Western Australia are among the most geochemically extreme on Earth. This ephemeral saline lake is characterized by pH as low as 1.6 salinity as high as 32% total dissolved solids, and unusually complex geochemistry, including extremely high concentrations of aluminum, silica, and iron. We examined the microbial composition and putative function in this extreme acid brine environment by analyzing lake water, groundwater, and sediment samples collected during the austral summer near peak evapoconcentration. Our results reveal that the lake water metagenome, surprisingly, was comprised of mostly eukaryote sequences, particularly fungi and to a lesser extent, green algae. Groundwater and sediment samples were dominated by acidophilic Firmicutes, with eukaryotic community members only detected at low abundances. The lake water bacterial community was less diverse than that in groundwater and sediment, and was overwhelmingly represented by a single OTU affiliated with Salinisphaera. Pathways associated with halotolerance were found in the metagenomes, as were genes associated with biosynthesis of protective carotenoids. During periods of complete desiccation of the lake, we hypothesize that dormancy and entrapment in fluid inclusions in halite crystals may increase long-term survival, leading to the resilience of complex eukaryotes in this extreme environment.

High-quality draft genome sequence of Effusibacillus lacus strain skLN1T, facultative anaerobic spore-former isolated from freshwater lake sediment

10.1601/nm.25721 strain skLN1T is the type strain of the type species in the genus 10.1601/nm.25720 which is the one of the genera in the family 10.1601/nm.5070 within the phylum 10.1601/nm.3874. 10.1601/nm.25721 strain skLN1T is a Gram-positive, spore-forming thermophilic neutrophile isolated from freshwater lake sediment. Here, we present the draft genome sequence of strain skLN1T, which consists of 3,902,380 bp with a G + C content of 50.38%.

Continuous ohmic heating of commercially processed apple juice using five sequential electric fields results in rapid inactivation of Alicyclobacillus acidoterrestris spores

Spores of Alicyclobacillus acidoterrestris, a spoilage bacterium, cause problems for the apple juice industry because they are resistant to thermal treatment. Here, we examined the sporicidal effect of an ohmic heating (OH) system with five sequential electric fields and compared it with that of conventional heating. Apple juice product (50kg) inoculated with A. acidoterrestris spores were subjected to OH (electric field strength=26.7V/cm; frequency=25kHz) at 85-100°C for 30-90s. The effect of conventional heating was also examined under these conditions. OH treatment at 100°C for 30s resulted in total inactivation of the inoculum, with no recovery of viable cells (initial population=4.8-4.9logCFU/ml), whereas 3.6-4.9logCFU/ml of the spores survived conventional heating. OH did not alter the quality (°Brix, color, and pH) of commercial apple juice (p>0.05). These results suggest that the OH system is superior to conventional heating for rapid sterilization (30s) of apple juice to assure microbiological quality in the absence of chemical additives.