Halophilic lactic acid bacteria - Play a vital role in the fermented food industry

Halophilic lactic acid bacteria have been widely found in various high-salt fermented foods. The distribution of these species in salt-fermented foods contributes significantly to the development of the product's flavor. Besides, these bacteria also have the ability to biosynthesize bioactive components which potentially apply to different areas. In this review, insights into the metabolic properties, salt stress responses, and potential applications of these bacteria have been have been elucidated. The purpose of this review highlights the important role of halophilic lactic acid bacteria in improving the quality and safety of salt-fermented products and explores the potential application of these bacteria.

Microbial Diversity Impacts Non-Protein Amino Acid Production in Cyanobacterial Bloom Cultures Collected from Lake Winnipeg

Lake Winnipeg in Manitoba, Canada is heavily impacted by harmful algal blooms that contain non-protein amino acids (NPAAs) produced by cyanobacteria: N-(2-aminoethyl)glycine (AEG), β-aminomethyl-L-alanine (BAMA), β-N-methylamino-L-alanine (BMAA), and 2,4-diaminobutyric acid (DAB). Our objective was to investigate the impact of microbial diversity on NPAA production by cyanobacteria using semi-purified crude cyanobacterial cultures established from field samples collected by the Lake Winnipeg Research Consortium between 2016 and 2021. NPAAs were detected and quantified by ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) using validated analytical methods, while Shannon and Simpson alpha diversity scores were determined from 16S rRNA metagenomic sequences. Alpha diversity in isolate cultures was significantly decreased compared to crude cyanobacterial cultures (p < 0.001), indicating successful semi-purification. BMAA and AEG concentrations were higher in crude compared to isolate cultures (p < 0.0001), and AEG concentrations were correlated to the alpha diversity in cultures (r = 0.554; p < 0.0001). BAMA concentrations were increased in isolate cultures (p < 0.05), while DAB concentrations were similar in crude and isolate cultures. These results demonstrate that microbial community complexity impacts NPAA production by cyanobacteria and related organisms.

Isolation and characterization of bioprotective lactic acid bacteria from Moroccan fish and seafood

The microbiota of aquatic animals is heavily influenced by their environment, offering a potential source for biotechnologically relevant microorganisms. In this investigation, bacterial strains from fish and fish products were investigated to determine their antimicrobial effects against fish and food pathogens. Twelve strains, including five Lactococcus, two Enterococcus hirae, two Enterococcus mundtii, and three Latilactobacillus sakei were selected as producing bacteriocin-like substances with antimicrobial properties that were active against a broad spectrum of bacteria, such as Listeria monocytogenes, Staphylococcus aureus, and Pseudomonas aeruginosa. Selected strains were identified via 16S rRNA sequencing. Most strains exhibited sensitivity to eight types of antibiotics (erythromycin, tetracycline, chloramphenicol, vancomycin, fosfomycin, gentamicin, ampicillin, and netilmicin), lacked hemolysin and gelatinase virulence factors, and did not produce histamine. These findings suggest that marine fish may be a promising source of lactic acid bacteria strains with antimicrobial potential for use as biopreservatives in the food industry.

Deep Isolated Aquifer Brines Harbor Atypical Halophilic Microbial Communities in Quebec, Canada

The deep terrestrial subsurface, hundreds of meters to kilometers below the surface, is characterized by oligotrophic conditions, dark and often anoxic settings, with fluctuating pH, salinity, and water availability. Despite this, microbial populations are detected and active, contributing to biogeochemical cycles over geological time. Because it is extremely difficult to access the deep biosphere, little is known about the identity and metabolisms of these communities, although they likely possess unknown pathways and might interfere with deep waste deposits. Therefore, we analyzed rock and groundwater microbial communities from deep, isolated brine aquifers in two regions dating back to the Ordovician and Devonian, using amplicon and whole genome sequencing. We observed significant differences in diversity and community structure between both regions, suggesting an impact of site age and composition. The deep hypersaline groundwater did not contain typical halophilic bacteria, and genomes suggested pathways involved in protein and hydrocarbon degradation, and carbon fixation. We identified mainly one strategy to cope with osmotic stress: compatible solute uptake and biosynthesis. Finally, we detected many bacteriophage families, potentially indicating that bacteria are infected. However, we also found auxiliary metabolic genes in the viral genomes, probably conferring an advantage to the infected hosts.

Adaptive growth and acidogenic fermentation performance of haloalkaliphilic bacterial communities enriched from biofilms colonising strongly alkaline and saline bauxite residue

The present study aimed to characterise the adaptive growth and acidogenic fermentation performance of haloalkaliphilic bacteria sourced from field biofilms colonising seawater-treated bauxite residue, under moderate and extremely alkaline pH conditions (8.5 to 10.8) and coupled saline (EC ≈ 50 mS/cm) conditions. The haloalkaliphilic bacterial communities demonstrated strong adaptiveness to the increasing pH from 8.5 to 10.8. The dominant groups were Exiguobacterales and Bacillales at pH 8.5 and 10, but Lactobacillales and Bacillales at pH 10.8. The exposure to pH 10.8 initially delayed bacterial growth in the first 24 h, but which rapidly recovered to a peak rate at 48 h similar to that in the pH 10 treatment. Correspondingly, lactic acid concentration at pH 10.8 rapidly rose to as high as >2000 mg/L at 48 h. Bacterial growth and organic acid production were positively related to carbohydrate supply. Overall, these bacterial groups fermented glucose to produce mainly lactic acid (>80 %) and other acids (such as acetic acid, formic acid, and succinic acid), leading to 0.5-2.0 units of pH reduction, despite the strong buffering capacity in the culture solution. The bacteria could up-regulate their phosphatase activity to mineralise the organic P in the basal nutrient broth, but increasing soluble phosphate-P at a 1:10 of glucose-C was beneficial. The biofilm-sourced bacteria communities contained redundant fermentative haloalkaliphilic groups which were adaptive to strongly alkaline pH and saline conditions.

Leaching composition and associated microbial community of recycled concrete aggregate (RCA)

Recycled concrete aggregate (RCA) has been used as an alternative sustainable material in the construction industry, but RCA long-term environmental impacts are unknown. In this study, the bacterial enrichment potential to reduce the alkalinity of two different types of RCA was examined, from laboratory-produced concrete and from a stockpile of demolished concrete that had been in service in transportation applications. Washed and un-washed lab and field RCA were biostimulated by being exposed to ATCC® Medium 661 in batch experiments. pH, metal composition and microbial community changes in the leachates were monitored over time. Results show that initial pH of field RCA leachate could be decreased to less concerning values, as low as 8, but concentrations of some metals in the leachate exceeded groundwater quality standards. However, the biostimulated RCA released lower metal concentration and was more resistant to pH increases than non-biostimulated RCA during a long-term leaching experiment with DI water. The microbial community was enriched on anaerobic, halotolerant and alkaliphile microorganisms, resistant to extreme environmental conditions. The outcome of this research suggests a baseline for field RCA pretreatment before field application, using a biostimulation method that would generate a less environmentally detrimental runoff.

Investigation of microbial metabolisms in an extremely high pH marine-like terrestrial serpentinizing system: Ney Springs

Ney Springs, a continental serpentinizing spring in northern California, has an exceptionally high reported pH (12.4) for a naturally occurring water source. With high conductivity fluids, it is geochemically more akin to marine serpentinizing systems than other terrestrial locations. Our geochemical analyses also revealed high sulfide concentrations (544 mg/L) and methane emissions (83% volume gas content) relative to other serpentinizing systems. Thermodynamic calculations were used to investigate the potential for substrates resulting from serpentinization to fuel microbial life, and were found to support the energetic feasibility of sulfate reduction, anaerobic methane oxidation, denitrification, and anaerobic sulfide oxidation within this system. Assessment of the microbial community via 16S rRNA taxonomic gene surveys and metagenome sequencing revealed a community composition dominated by poorly characterized members of the Izemoplasmatales and Clostridiales. The genomes of these dominant taxa point to a fermentative lifestyle, though other highly complete (>90%) metagenome assembled genomes support the potential for organisms to perform sulfate reduction, sulfur disproportionation and/or sulfur oxidation (aerobic and anaerobic). Two chemolithoheterotrophs identified in the metagenome, a Halomonas sp. and a Rhodobacteraceae sp., were isolated and shown to oxidize thiosulfate and were capable of growth in conditions up to pH 12.4. Despite being characteristic products of serpentinization reactions, little evidence was seen for hydrogen and methane utilization in the Ney Springs microbial community. Hydrogen is not highly abundant and could be consumed prior to reaching the spring community. Other metabolic strategies may be outcompeted by more energetically favorable heterotrophic or fermentation reactions, or even inhibited by other compounds in the spring such as ammonia. The unique geochemistry of Ney Springs provides an opportunity to study how local geology interacts with serpentinized fluids, while its microbial community can better inform us of the metabolic strategies employed in hyperalkaline environments.

Distinguishing the milk microbiota of healthy goats and goats diagnosed with subclinical mastitis, clinical mastitis, and gangrenous mastitis

Mastitis, mainly caused by bacterial intramammary infections, is the main problem in the breeding of dairy animals. The inflammations of the mammary gland is separated by types of mastitis, being subclinical, clinical, and the most severe, gangrenous mastitis. Here, we used 16S rRNA amplicon sequencing to characterize the bacterial microbiota of goat milk in the different types of goat mastitis caused by bacteria. We used 72 goat milk samples from a region of the state of Minas Gerais in Brazil, of which 12 were from clinically healthy animals, 42 from animals diagnosed with subclinical mastitis, 16 from animals with clinical mastitis, and 2 from animals with gangrenous mastitis. The group related to gangrenous mastitis was the most divergent in terms of alpha and beta diversity. The most abundant genus among samples of the groups was Staphylococcus spp., and we found a high abundance of Mycoplasma sp. in the milk of animals diagnosed with clinical mastitis. The most statistically relevant microorganisms among the groups were Prevotella sp., Ruminococcaceae, Prevotella ruminicola sp., and Providencia sp. We highlight a new association of bacterial agents in gangrenous mastitis among Escherichia sp./Shigella sp. and Enterococcus sp. and provide the second report of the genus Alkalibacterium sp., in milk samples. Only the taxa Staphylococcus sp., Bacteroides sp., Enterococcus, and Brevidabacterium sp., were present in all groups. The superpathway of L-tryptophan biosynthesis metabolites and the sucrose degradation III (sucrose invertase) pathway were the most prominent ones among the groups. In this study, we demonstrate how a rich microbiota of goat milk from healthy animals can be altered during the aggravation of different types of mastitis, in addition to demonstrating new bacterial genera in milk not previously detected in other studies as well as new associations between agents.

Effect of Intramammary Dry Cow Antimicrobial Treatment on Fresh Cow's Milk Microbiota in California Commercial Dairies

This study used 16S rRNA sequencing to evaluate the effects of dry cow antimicrobial therapy on the udder milk microbiota by comparing the microbial populations in milk at dry-off (DRY) (~60 days before calving) and post-partum (FRESH) (4-11 days after calving) from cows receiving an intramammary antibiotic infusion prior to dry-off (IMT) and cows that did not receive treatment (CTL). Milk was collected from 23 cows from the IMT group and 27 cows from the CTL group. IMT and DRY samples had a greater correlation with the genera Brevibacterium and Amaricoccus, and the family Micrococcaceae, when compared to IMT and FRESH samples. CTL group samples collected at DRY had a greater correlation with the genera Akkermansia and Syntrophus, when compared to FRESH samples; no bacterial taxa were observed to have a significant correlation with FRESH samples in the CTL group. DRY samples collected from the CTL group had a greater correlation with the genus Mogibacterium when compared to IMT and CTL samples. For DRY samples collected from the IMT group, a greater correlation with the genus Alkalibacterium when compared to DRY and CTL samples, was observed. The lack of a correlation for FRESH samples between the CTL and IMT treatment groups indicated that intramammary antimicrobial dry cow therapy had no significant effect on the udder milk microbiota post-partum.

Dynamic Changes in the Bacterial Community and Metabolic Profile during Fermentation of Low-Salt Shrimp Paste (Terasi)

Low-salt shrimp paste, or terasi, is an Indonesian fermented food made from planktonic shrimp mixed with a low concentration of salt. Since high daily intake of sodium is deemed unhealthy, reduction of salt content in shrimp paste production is desired. Until now, there is no reported investigation on the bacterial population and metabolite composition of terasi during fermentation. In this study, the bacterial community of terasi was assessed using high-throughput sequencing of the 16S rRNA V3–V4 region. From this analysis, Tetragenococcus, Aloicoccus, Alkalibacillus, Atopostipes, and Alkalibacterium were found to be the dominant bacterial genus in low-salt shrimp paste. GC/MS-based metabolite profiling was also conducted to monitor the metabolite changes during shrimp paste fermentation. Results showed that acetylated amino acids increased, while glutamine levels decreased, during the fermentation of low-salt shrimp paste. At the start of shrimp paste fermentation, Tetragenococcus predominated with histamine and cadaverine accumulation. At the end of fermentation, there was an increase in 4-hydroxyphenyl acetic acid and indole-3-acetic acid levels, as well as the predominance of Atopostipes. Moreover, we found that aspartic acid increased during fermentation. Based on our findings, we recommend that fermentation of low-salt shrimp paste be done for 7 to 21 days, in order to produce shrimp paste that has high nutritional content and reduced health risk.

Determination of microbial diversities and aroma characteristics of Beitang shrimp paste

Beitang shrimp paste (BSP) is fermented by different parts of shrimp, such as the head (H), meat (M), or the whole shrimp (S and W). Microbial communities of BSP were dominated by Firmicutes and Proteobacteria at the phyla level and Tetragenococcus at the genus level. However, the microbial diversity of M was the lowest than the others. Non-dominant bacterial communities were presented by a mutual symbiotic model in BSP fermentation. Tetragenococcus, Halanaerobium, Streptococcus, and Brevundimonas were positively correlated with the biosynthesis of amino acids, fatty acids, and metabolic cofactors; Marinilactibacillus and Pseudomonas might be the main contributors to inorganic sulfides, nitrogen oxides, and long-chain alkanes in BSP; Psychrobacter was closely related to the ester characteristics of methyl palmitoleate and methyl hexadecanoate in H. Halanaerobium and Streptococcus promoted the production of pyrazines in S. Tetragenococcus was positively correlated with acetic acid, decanoic acid, and palmitic acid that improved the sour aroma of M. The relationship between bacteria and aroma formation under different raw materials was expected to improve the quality of BSP.

Performance and Application of 16S rRNA Gene Cycle Sequencing for Routine Identification of Bacteria in the Clinical Microbiology Laboratory

This review provides a state-of-the-art description of the performance of Sanger cycle sequencing of the 16S rRNA gene for routine identification of bacteria in the clinical microbiology laboratory. A detailed description of the technology and current methodology is outlined with a major focus on proper data analyses and interpretation of sequences. The remainder of the article is focused on a comprehensive evaluation of the application of this method for identification of bacterial pathogens based on analyses of 16S multialignment sequences. In particular, the existing limitations of similarity within 16S for genus- and species-level differentiation of clinically relevant pathogens and the lack of sequence data currently available in public databases is highlighted. A multiyear experience is described of a large regional clinical microbiology service with direct 16S broad-range PCR followed by cycle sequencing for direct detection of pathogens in appropriate clinical samples. The ability of proteomics (matrix-assisted desorption ionization-time of flight) versus 16S sequencing for bacterial identification and genotyping is compared. Finally, the potential for whole-genome analysis by next-generation sequencing (NGS) to replace 16S sequencing for routine diagnostic use is presented for several applications, including the barriers that must be overcome to fully implement newer genomic methods in clinical microbiology. A future challenge for large clinical, reference, and research laboratories, as well as for industry, will be the translation of vast amounts of accrued NGS microbial data into convenient algorithm testing schemes for various applications (i.e., microbial identification, genotyping, and metagenomics and microbiome analyses) so that clinically relevant information can be reported to physicians in a format that is understood and actionable. These challenges will not be faced by clinical microbiologists alone but by every scientist involved in a domain where natural diversity of genes and gene sequences plays a critical role in disease, health, pathogenicity, epidemiology, and other aspects of life-forms. Overcoming these challenges will require global multidisciplinary efforts across fields that do not normally interact with the clinical arena to make vast amounts of sequencing data clinically interpretable and actionable at the bedside.

Halophilic & halotolerant prokaryotes in humans

Halophilic prokaryotes are described as microorganisms living in hypersaline environments. Here, we list the halotolerant and halophilic bacteria which have been isolated in humans. Of the 52 halophilic prokaryotes, 32 (61.54%) were moderately halophilic, 17 (32.69%) were slightly halophilic and three (5.76%) were extremely halophilic prokaryotes. At the phylum level, 29 (54.72%) belong to Firmicutes, 15 (28.84%) to Proteobacteria, four (7.69%) to Actinobacteria, three (5.78%) to Euryarchaeota and one (1.92%) belongs to Bacteroidetes. Halophilic prokaryotes are rarely pathogenic: of these 52 halophilic prokaryotes only two (3.92%) species were classified in Risk Group 2 (Vibrio cholerae, Vibrio parahaemolyticus) and one (1.96%), species in Risk Group 3 (Bacillus anthracis).

Wood Ash Induced pH Changes Strongly Affect Soil Bacterial Numbers and Community Composition

Recirculation of wood ash from energy production to forest soil improves the sustainability of this energy production form as recycled wood ash contains nutrients that otherwise would be lost at harvest. In addition, wood-ash is beneficial to many soils due to its inherent acid-neutralizing capabilities. However, wood ash has several ecosystem-perturbing effects like increased soil pH and pore water electrical conductivity both known to strongly impact soil bacterial numbers and community composition. Studies investigating soil bacterial community responses to wood ash application remain sparse and the available results are ambiguous and remain at a general taxonomic level. Here we investigate the response of bacterial communities in a spruce forest soil to wood ash addition corresponding to 0, 5, 22, and 167 t wood ash ha^-1. We used culture-based enumerations of general bacteria, Pseudomonas and sporeforming bacteria combined with 16S rRNA gene amplicon sequencing to valuate soil bacterial responses to wood ash application. Results showed that wood ash addition strongly increased soil pH and electrical conductivity. Soil pH increased from acidic through neutral at 22 t ha^-1 to alkaline at 167 t ha^-1. Bacterial numbers significantly increased up to a wood ash dose of 22 t ha^-1 followed by significant decrease at 167 t ha^-1 wood ash. The soil bacterial community composition changed after wood ash application with copiotrophic bacteria responding positively up to a wood ash dose of 22 t ha^-1 while the adverse effect was seen for oligotrophic bacteria. Marked changes in bacterial community composition occurred at a wood ash dose of 167 t ha^-1 with a single alkaliphilic genus dominating. Additionally, spore-formers became abundant at an ash dose of 167 t ha^-1 whereas this was not the case at lower ash doses. Lastly, bacterial richness and diversity strongly decreased with increasing amount of wood ash applied. All of the observed bacterial responses can be directly explained by the wood ash induced changes in pH, electrical conductivity and the addition of wood ash inherent nutrients.

Alkaline bioleaching of municipal solid waste incineration fly ash by autochthonous extremophiles

The increasing demand for energy and the generation of solid waste have caused an alarming rise in fly ash production globally. Since heavy metals continue to be in demand for the production of materials, resource recovery from the recycling of these wastes has the potential to delay the depletion of natural ores. The use of microorganisms for the leaching of metals, in a process called bioleaching, is an eco-friendly and economical way to treat the metal-laden wastes. Bioleaching of fly ash is challenging due largely to the alkaline nature and toxic levels of heavy metals which are detrimental to microbial growth and bioleaching activity. The present work reports the isolation of indigenous bacteria from a local landfill site and their bioleaching performance [corrected]. 38 autochthonous strains of bacteria were isolated from eight samples collected and plated on five different media. 18 of the isolates showed bioleaching potential, with significant alkaline pH or fly ash tolerance. Genetic characterization of the strains revealed a dominance of Firmicutes, with Alkalibacterium sp. TRTYP6 showing highest fly ash tolerance of up to 20% w/v fly ash, and growth over a pH range 8-12.5. The organism selectively recovered about 52% Cu from the waste. To the best of our knowledge, this is the first time a study on bioleaching with extreme alkaliphiles is reported.

Halophiles: biology, adaptation, and their role in decontamination of hypersaline environments

The unique cellular enzymatic machinery of halophilic microbes allows them to thrive in extreme saline environments. That these microorganisms can prosper in hypersaline environments has been correlated with the elevated acidic amino acid content in their proteins, which increase the negative protein surface potential. Because these microorganisms effectively use hydrocarbons as their sole carbon and energy sources, they may prove to be valuable bioremediation agents for the treatment of saline effluents and hypersaline waters contaminated with toxic compounds that are resistant to degradation. This review highlights the various strategies adopted by halophiles to compensate for their saline surroundings and includes descriptions of recent studies that have used these microorganisms for bioremediation of environments contaminated by petroleum hydrocarbons. The known halotolerant dehalogenase-producing microbes, their dehalogenation mechanisms, and how their proteins are stabilized is also reviewed. In view of their robustness in saline environments, efforts to document their full potential regarding remediation of contaminated hypersaline ecosystems merits further exploration.

Production of volatile fatty acids from sewage organic matter by combined bioflocculation and alkaline fermentation

This study explored the potential of volatile fatty acids (VFA) production from sewage by a combined high-loaded membrane bioreactor and sequencing batch fermenter. VFA production was optimized with respect to SRT and alkaline pH (pH 8-10). Application of pH shock to a value of 9 at the start of a sequencing batch cycle, followed by a pH uncontrolled phase for 7days, gave the highest VFA yield of 440mgVFA-COD/g VSS. This yield was much higher than at fermentation without pH control or at a constant pH between 8 and 10. The high yield in the pH 9 shocked system could be explained by (1) a reduction of methanogenic activity, or (2) a high degree of solids degradation or (3) an enhanced protein hydrolysis and fermentation. VFA production can be further optimized by fine-tuning pH level and longer operation, possibly allowing enrichment of alkalophilic and alkali-tolerant fermenting microorganisms.

Bacterial community structure of a lab-scale anammox membrane bioreactor

Autotrophic nitrogen removal technologies have proliferated through the last decade. Among these, a promising one is the membrane bioreactor (MBR) Anammox, which can achieve very high solids retention time and therefore sets a proper environment for the cultivation of anammox bacteria. In this sense, the MBR Anammox is an efficient technology for the treatment of effluents with low organic carbon and high ammonium concentrations once it has been treated under partial nitrification systems. A lab-scale MBR Anammox bioreactor has been built at the Technological University of Delft, The Netherlands and has been proven for efficient nitrogen removal and efficient cultivation of anammox bacteria. In this study, next-generation sequencing techniques have been used for the investigation of the bacterial communities of this MBR Anammox for the first time ever. A strong domination of Candidatus Brocadia bacterium and also the presence of a myriad of other microorganisms that have adapted to this environment were detected, suggesting that the MBR Anammox bioreactor might have a more complex microbial ecosystem that it has been thought. Among these, nitrate-reducing heterotrophs and primary producers, among others, were identified. Definition of the ecological roles of the OTUs identified through metagenomic analysis was discussed.

Identification of anaerobic arsenite-oxidizing and arsenate-reducing bacteria associated with an alkaline saline lake in Khovsgol, Mongolia

Microbial arsenic transformation pathways associated with a saline lake located in northern Mongolia were examined using molecular biological and culturing approaches. Bacterial 16S rRNA gene sequences recovered from saline lake sediments and soils were affiliated with haloalkaliphiles, including Bacillus and Halomonas spp. Diverse sequences of arsenate respiratory reductase (arrA) and a new group of arsenite oxidase (arxA) genes were also identified. Pure cultures of arsenate-reducing Nitrincola strain and anaerobic arsenite-oxidizing Halomonas strain were isolated. The chemoorganotrophic Halomonas strain contains arxA gene similar to that of a chemoautotrophic arsenite-oxidizing Alkalilimnicola ehrlichii strain MLHE-1. These results revealed the diversity of arsenic transformation pathways associated with a geographically distinct saline system and the potential contribution of arx-dependent arsenite oxidation by heterotrophic bacteria.

Alkalibacterium gilvum sp. nov., slightly halophilic and alkaliphilic lactic acid bacterium isolated from soft and semi-hard cheeses

Nine novel strains of halophilic and alkaliphilic lactic acid bacteria isolated from European soft and semi-hard cheeses by using a saline, alkaline medium (7 % NaCl, pH 9.5) were taxonomically characterized. The isolates were Gram-stain-positive, non-sporulating and non-motile. They lacked catalase and quinones. Under anaerobic cultivation conditions, lactate was produced from d-glucose with the production of formate, acetate and ethanol with a molar ratio of approximately 2 : 1 : 1. Under aerobic cultivation conditions, acetate and lactate were produced from d-glucose. The isolates were slightly halophilic, highly halotolerant and alkaliphilic. The optimum NaCl concentration for growth ranged between 2.0 % and 5.0 % (w/v), with a growth range of 0–1 % to 15–17.5 %. The optimum pH for growth ranged between 8.5 and 9.5, with a growth range of 7.0–7.5 to 9.5–10.0. Comparative sequence analysis of the 16S rRNA genes revealed that the isolates occupied a phylogenetic position within the genus Alkalibacterium , showing the highest sequence similarity (98.2 %) to Alkalibacterium kapii T22-1-2T. The isolates constituted a single genomic species with DNA–DNA hybridization values of 79–100 % among the isolates and <29 % between the isolates and other members of the genus Alkalibacterium , from which the isolates were different in motility and flagellation, growth responses to NaCl concentrations and pH, and profiles of sugar fermentation. The DNA G+C contents were between 36.0 and 37.6 mol%. The cell-wall peptidoglycan was type A4β, Orn-d-Asp. The major components of cellular fatty acids were C14 : 0, C16 : 0 and C16 : 1ω9c. Based on the phenotypic characteristics and genetic distinctness, the isolates are classified as a novel species within the genus Alkalibacterium , for which the name Alkalibacterium gilvum sp. nov. is proposed. The type strain is 3AD-1T ( = DSM 25751T = JCM 18271T).

Response mechanisms of lactic acid bacteria to alkaline environments: a review

Regulation of the cytoplasmic or internal pH (pHin) is a fundamental requirement for the survival and viability of bacteria. The optimum pHin for most bacteria is near the neutral point (pH 7.0). Therefore, bacteria may have some strategies to adapt themselves to the acidity or alkalinity of cytoplasm. As other microorganisms, lactic acid bacteria (LAB) are able to maintain a neutral or near neutral cytoplasmic pH even when the pH of the external medium varies. Mechanisms facilitating survival and growth under alkaline conditions of LAB are reviewed. These mechanisms are: (i) the active potassium extrusion and the potassium-proton antiport system, (ii) the sodium-proton antiport system, (iii) the proton-translocating adenosine triphosphatase (ATPase), (iv) the formation of transmembrane proton gradients (ΔpH) in a reversed direction, and (v) the adaptation, cross-protection, and changes in protein synthesis.

Alkalibacterium subtropicum sp. nov., a slightly halophilic and alkaliphilic marine lactic acid bacterium isolated from decaying marine algae

Two novel strains of marine lactic acid bacteria, isolated from decaying marine algae collected from a subtropical area of Japan, are described. The isolates, designated O24-2(T) and O25-2, were Gram-positive, non-sporulating and non-motile. They lacked catalase and quinones. Under anaerobic cultivation conditions, lactate was produced from glucose with the production of formate, acetate and ethanol in a molar ratio of approximately 2:1:1. Under aerobic cultivation conditions, acetate and lactate were produced from carbohydrates and related compounds. The isolates were slightly halophilic, highly halotolerant and alkaliphilic. They were able to grow in 0-17.0% (w/v) NaCl, with optimum growth of strains O24-2(T) and O25-2 at 1.0-3.0 and 1.0-2.0% (w/v) NaCl, respectively. Growth of strain O24-2(T) was observed at pH 7.5-9.5, with optimum growth at pH 8.0-8.5. Comparative 16S rRNA gene sequence analysis revealed that the isolates occupied a phylogenetic position within the genus Alkalibacterium, showing highest similarity (99.6%) to Alkalibacterium putridalgicola T129-2-1(T). Although sequence similarity was high, the DNA-DNA relatedness value between strain O24-2(T) and A. putridalgicola T129-2-1(T) was 27%, indicating that they are members of distinct species. The DNA G+C contents of O24-2(T) and O25-2 were 43.7 and 44.4 mol%, respectively, and DNA-DNA relatedness between the isolates was 89%. The cell-wall peptidoglycan was type A4β, Orn-d-Asp. The major cellular fatty acid components were C(14:0), C(16:0) and C(16:1)ω9c. Based on phenotypic characteristics and genetic distinctiveness, the isolates were classified as representatives of a novel species within the genus Alkalibacterium, for which the name Alkalibacterium subtropicum sp. nov. is proposed; the type strain is O24-2(T) (=DSM 23664(T)=NBRC 107172(T)).

Population dynamics of two antilisterial cheese surface consortia revealed by temporal temperature gradient gel electrophoresis

Background

Surface contamination of smear cheese by Listeria spp. is of major concern for the industry. Complex smear ecosystems have been shown to harbor antilisterial potential but the microorganisms and mechanisms involved in the inhibition mostly remain unclear, and are likely related to complex interactions than to production of single antimicrobial compounds. Bacterial biodiversity and population dynamics of complex smear ecosystems exhibiting antilisterial properties in situ were investigated by Temporal temperature gradient gel electrophoresis (TTGE), a culture independent technique, for two microbial consortia isolated from commercial Raclette type cheeses inoculated with defined commercial ripening cultures (F) or produced with an old-young smearing process (M).

Results

TTGE revealed nine bacterial species common to both F and M consortia, but consortium F exhibited a higher diversity than consortium M, with thirteen and ten species, respectively. Population dynamics were studied after application of the consortia on fresh-produced Raclette cheeses. TTGE analyses revealed a similar sequential development of the nine species common to both consortia. Beside common cheese surface bacteria (Staphylococcus equorum, Corynebacterium spp., Brevibacterium linens, Microbacterium gubbeenense, Agrococcus casei), the two consortia contained marine lactic acid bacteria (Alkalibacterium kapii, Marinilactibacillus psychrotolerans) that developed early in ripening (day 14 to 20), shortly after the growth of staphylococci (day 7). A decrease of Listeria counts was observed on cheese surface inoculated at day 7 with 0.1-1 × 10² CFU cm^-2, when cheeses were smeared with consortium F or M. Listeria counts went below the detection limit of the method between day 14 and 28 and no subsequent regrowth was detected over 60 to 80 ripening days. In contrast, Listeria grew to high counts (10⁵ CFU cm^-2) on cheeses smeared with a defined surface culture.

Conclusions

This work reports the first population dynamics study of complex smear ecosystems exhibiting in situ antilisterial activity. TTGE revealed the presence of marine lactic acid bacteria that are likely related to the strong Listeria inhibition, as their early development in the smear occurred simultaneously with a decrease in Listeria cell count.