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Dicks LMT. Biofilm Formation of Clostridioides difficile, Toxin Production and Alternatives to Conventional Antibiotics in the Treatment of CDI. Microorganisms 2023; 11:2161. [PMID: 37764005 PMCID: PMC10534356 DOI: 10.3390/microorganisms11092161] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2023] [Revised: 08/16/2023] [Accepted: 08/24/2023] [Indexed: 09/29/2023] Open
Abstract
Clostridioides difficile is considered a nosocomial pathogen that flares up in patients exposed to antibiotic treatment. However, four out of ten patients diagnosed with C. difficile infection (CDI) acquired the infection from non-hospitalized individuals, many of whom have not been treated with antibiotics. Treatment of recurrent CDI (rCDI) with antibiotics, especially vancomycin (VAN) and metronidazole (MNZ), increases the risk of experiencing a relapse by as much as 70%. Fidaxomicin, on the other hand, proved more effective than VAN and MNZ by preventing the initial transcription of RNA toxin genes. Alternative forms of treatment include quorum quenching (QQ) that blocks toxin synthesis, binding of small anion molecules such as tolevamer to toxins, monoclonal antibodies, such as bezlotoxumab and actoxumab, bacteriophage therapy, probiotics, and fecal microbial transplants (FMTs). This review summarizes factors that affect the colonization of C. difficile and the pathogenicity of toxins TcdA and TcdB. The different approaches experimented with in the destruction of C. difficile and treatment of CDI are evaluated.
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Affiliation(s)
- Leon M T Dicks
- Department of Microbiology, Stellenbosch University, Stellenbosch 7600, South Africa
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2
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Co-culture fermentation characteristics of antifreeze yeast and mining of related freezing-resistant genes. Eur Food Res Technol 2023. [DOI: 10.1007/s00217-023-04204-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
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3
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Mechanisms of Stress Tolerance in Cyanobacteria under Extreme Conditions. STRESSES 2022. [DOI: 10.3390/stresses2040036] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Cyanobacteria are oxygen-evolving photoautotrophs with worldwide distribution in every possible habitat, and they account for half of the global primary productivity. Because of their ability to thrive in a hostile environment, cyanobacteria are categorized as “extremophiles”. They have evolved a fascinating repository of distinct secondary metabolites and biomolecules to promote their development and survival in various habitats, including severe conditions. However, developing new proteins/enzymes and metabolites is mostly directed by an appropriate gene regulation system that results in stress adaptations. However, only few proteins have been characterized to date that have the potential to improve resistance against abiotic stresses. As a result, studying environmental stress responses to post-genomic analysis, such as proteome changes using latest structural proteomics and synthetic biology techniques, is critical. In this regard, scientists working on these topics will benefit greatly from the stress of proteomics research. Progress in these disciplines will aid in understanding cyanobacteria’s physiology, biochemical, and metabolic systems. This review summarizes the most recent key findings of cyanobacterial proteome study under various abiotic stresses and the application of secondary metabolites formed during different abiotic conditions.
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4
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Li J, Ran X, Zhou M, Wang K, Wang H, Wang Y. Oxidative stress and antioxidant mechanisms of obligate anaerobes involved in biological waste treatment processes: A review. THE SCIENCE OF THE TOTAL ENVIRONMENT 2022; 838:156454. [PMID: 35667421 DOI: 10.1016/j.scitotenv.2022.156454] [Citation(s) in RCA: 13] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/12/2022] [Revised: 05/23/2022] [Accepted: 05/31/2022] [Indexed: 06/15/2023]
Abstract
In-depth understanding of the molecular mechanisms and physiological consequences of oxidative stress is still limited for anaerobes. Anaerobic biotechnology has become widely accepted by the wastewater/sludge industry as a better alternative to more conventional but costly aerobic processes. However, the functional anaerobic microorganisms used in anaerobic biotechnology are frequently hampered by reactive oxygen/nitrogen species (ROS/RNS)-mediated oxidative stress caused by exposure to stressful factors (e.g., oxygen and heavy metals), which negatively impact treatment performance. Thus, identifying stressful factors and understanding antioxidative defense mechanisms of functional obligate anaerobes are crucial for the optimization of anaerobic bioprocesses. Herein, we present a comprehensive overview of oxidative stress and antioxidant mechanisms of obligate anaerobes involved in anaerobic bioprocesses; as examples, we focus on anaerobic ammonium oxidation bacteria and methanogenic archaea. We summarize the primary stress factors in anaerobic bioprocesses and the cellular antioxidant defense systems of functional anaerobes, a consortia of enzymatic and nonenzymatic mechanisms. The dual role of ROS/RNS in cellular processes is elaborated; at low concentrations, they have vital cell signaling functions, but at high concentrations, they cause oxidative damage. Finally, we highlight gaps in knowledge and future work to uncover antioxidant and damage repair mechanisms in obligate anaerobes. This review provides in-depth insights and guidance for future research on oxidative stress of obligate anaerobes to boost the accurate regulation of anaerobic bioprocesses in challenging and changing operating conditions.
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Affiliation(s)
- Jia Li
- State Key Laboratory of Pollution Control and Resources Reuse, Shanghai Institute of Pollution Control and Ecological Security, Tongji University, Shanghai 200092, China
| | - Xiaochuan Ran
- State Key Laboratory of Pollution Control and Resources Reuse, Shanghai Institute of Pollution Control and Ecological Security, Tongji University, Shanghai 200092, China
| | - Mingda Zhou
- State Key Laboratory of Pollution Control and Resources Reuse, Shanghai Institute of Pollution Control and Ecological Security, Tongji University, Shanghai 200092, China
| | - Kaichong Wang
- State Key Laboratory of Pollution Control and Resources Reuse, Shanghai Institute of Pollution Control and Ecological Security, Tongji University, Shanghai 200092, China
| | - Han Wang
- State Key Laboratory of Pollution Control and Resources Reuse, Shanghai Institute of Pollution Control and Ecological Security, Tongji University, Shanghai 200092, China.
| | - Yayi Wang
- State Key Laboratory of Pollution Control and Resources Reuse, Shanghai Institute of Pollution Control and Ecological Security, Tongji University, Shanghai 200092, China
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5
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Mavrommati M, Daskalaki A, Papanikolaou S, Aggelis G. Adaptive laboratory evolution principles and applications in industrial biotechnology. Biotechnol Adv 2021; 54:107795. [PMID: 34246744 DOI: 10.1016/j.biotechadv.2021.107795] [Citation(s) in RCA: 68] [Impact Index Per Article: 22.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2021] [Revised: 06/11/2021] [Accepted: 07/05/2021] [Indexed: 12/20/2022]
Abstract
Adaptive laboratory evolution (ALE) is an innovative approach for the generation of evolved microbial strains with desired characteristics, by implementing the rules of natural selection as presented in the Darwinian Theory, on the laboratory bench. New as it might be, it has already been used by several researchers for the amelioration of a variety of characteristics of widely used microorganisms in biotechnology. ALE is used as a tool for the deeper understanding of the genetic and/or metabolic pathways of evolution. Another important field targeted by ALE is the manufacturing of products of (high) added value, such as ethanol, butanol and lipids. In the current review, we discuss the basic principles and techniques of ALE, and then we focus on studies where it has been applied to bacteria, fungi and microalgae, aiming to improve their performance to biotechnological procedures and/or inspect the genetic background of evolution. We conclude that ALE is a promising and efficacious method that has already led to the acquisition of useful new microbiological strains in biotechnology and could possibly offer even more interesting results in the future.
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Affiliation(s)
- Maria Mavrommati
- Unit of Microbiology, Department of Biology, Division of Genetics, Cell Biology and Development, University of Patras, 26504 Patras, Greece; Laboratory of Food Microbiology and Biotechnology, Department of Food Science and Human Nutrition, Agricultural University of Athens, 75 Iera Odos, 11855 Athens, Greece
| | - Alexandra Daskalaki
- Unit of Microbiology, Department of Biology, Division of Genetics, Cell Biology and Development, University of Patras, 26504 Patras, Greece
| | - Seraphim Papanikolaou
- Laboratory of Food Microbiology and Biotechnology, Department of Food Science and Human Nutrition, Agricultural University of Athens, 75 Iera Odos, 11855 Athens, Greece
| | - George Aggelis
- Unit of Microbiology, Department of Biology, Division of Genetics, Cell Biology and Development, University of Patras, 26504 Patras, Greece.
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6
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Kim IS, Choi W, Son J, Lee JH, Lee H, Lee J, Shin SC, Kim HW. Screening and Genetic Network Analysis of Genes Involved in Freezing and Thawing Resistance in DaMDHAR-Expressing Saccharomyces cerevisiae Using Gene Expression Profiling. Genes (Basel) 2021; 12:genes12020219. [PMID: 33546197 PMCID: PMC7913288 DOI: 10.3390/genes12020219] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/30/2020] [Revised: 01/28/2021] [Accepted: 01/30/2021] [Indexed: 01/24/2023] Open
Abstract
The cryoprotection of cell activity is a key determinant in frozen-dough technology. Although several factors that contribute to freezing tolerance have been reported, the mechanism underlying the manner in which yeast cells respond to freezing and thawing (FT) stress is not well established. Therefore, the present study demonstrated the relationship between DaMDHAR encoding monodehydroascorbate reductase from Antarctic hairgrass Deschampsia antarctica and stress tolerance to repeated FT cycles (FT2) in transgenic yeast Saccharomyces cerevisiae. DaMDHAR-expressing yeast (DM) cells identified by immunoblotting analysis showed high tolerance to FT stress conditions, thereby causing lower damage for yeast cells than wild-type (WT) cells with empty vector alone. To detect FT2 tolerance-associated genes, 3′-quant RNA sequencing was employed using mRNA isolated from DM and WT cells exposed to FT (FT2) conditions. Approximately 332 genes showed ≥2-fold changes in DM cells and were classified into various groups according to their gene expression. The expressions of the changed genes were further confirmed using western blot analysis and biochemical assay. The upregulated expression of 197 genes was associated with pentose phosphate pathway, NADP metabolic process, metal ion homeostasis, sulfate assimilation, β-alanine metabolism, glycerol synthesis, and integral component of mitochondrial and plasma membrane (PM) in DM cells under FT2 stress, whereas the expression of the remaining 135 genes was partially related to protein processing, selenocompound metabolism, cell cycle arrest, oxidative phosphorylation, and α-glucoside transport under the same condition. With regard to transcription factors in DM cells, MSN4 and CIN5 were activated, but MSN2 and MGA1 were not. Regarding antioxidant systems and protein kinases in DM cells under FT stress, CTT1, GTO, GEX1, and YOL024W were upregulated, whereas AIF1, COX2, and TRX3 were not. Gene activation represented by transcription factors and enzymatic antioxidants appears to be associated with FT2-stress tolerance in transgenic yeast cells. RCK1, MET14, and SIP18, but not YPK2, have been known to be involved in the protein kinase-mediated signalling pathway and glycogen synthesis. Moreover, SPI18 and HSP12 encoding hydrophilin in the PM were detected. Therefore, it was concluded that the genetic network via the change of gene expression levels of multiple genes contributing to the stabilization and functionality of the mitochondria and PM, not of a single gene, might be the crucial determinant for FT tolerance in DaMDAHR-expressing transgenic yeast. These findings provide a foundation for elucidating the DaMDHAR-dependent molecular mechanism of the complex functional resistance in the cellular response to FT stress.
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Affiliation(s)
- Il-Sup Kim
- Advanced Bio-Resource Research Center, Kyungpook National University, Daegu 41566, Korea;
| | - Woong Choi
- Korea Polar Research Institute, Incheon 21990, Korea; (W.C.); (J.S.); (J.H.L.); (H.L.); (J.L.); (S.C.S.)
| | - Jonghyeon Son
- Korea Polar Research Institute, Incheon 21990, Korea; (W.C.); (J.S.); (J.H.L.); (H.L.); (J.L.); (S.C.S.)
| | - Jun Hyuck Lee
- Korea Polar Research Institute, Incheon 21990, Korea; (W.C.); (J.S.); (J.H.L.); (H.L.); (J.L.); (S.C.S.)
- Department of Polar Science, University of Science and Technology, Incheon 21990, Korea
| | - Hyoungseok Lee
- Korea Polar Research Institute, Incheon 21990, Korea; (W.C.); (J.S.); (J.H.L.); (H.L.); (J.L.); (S.C.S.)
- Department of Polar Science, University of Science and Technology, Incheon 21990, Korea
| | - Jungeun Lee
- Korea Polar Research Institute, Incheon 21990, Korea; (W.C.); (J.S.); (J.H.L.); (H.L.); (J.L.); (S.C.S.)
- Department of Polar Science, University of Science and Technology, Incheon 21990, Korea
| | - Seung Chul Shin
- Korea Polar Research Institute, Incheon 21990, Korea; (W.C.); (J.S.); (J.H.L.); (H.L.); (J.L.); (S.C.S.)
| | - Han-Woo Kim
- Korea Polar Research Institute, Incheon 21990, Korea; (W.C.); (J.S.); (J.H.L.); (H.L.); (J.L.); (S.C.S.)
- Department of Polar Science, University of Science and Technology, Incheon 21990, Korea
- Correspondence:
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7
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Slater RT, Frost LR, Jossi SE, Millard AD, Unnikrishnan M. Clostridioides difficile LuxS mediates inter-bacterial interactions within biofilms. Sci Rep 2019; 9:9903. [PMID: 31289293 PMCID: PMC6616478 DOI: 10.1038/s41598-019-46143-6] [Citation(s) in RCA: 37] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2019] [Accepted: 06/21/2019] [Indexed: 12/18/2022] Open
Abstract
The anaerobic gut pathogen, Clostridioides difficile, forms adherent biofilms that may play an important role in recurrent C. difficile infections. The mechanisms underlying C. difficile community formation and inter-bacterial interactions are nevertheless poorly understood. C. difficile produces AI-2, a quorum sensing molecule that modulates biofilm formation across many bacterial species. We found that a strain defective in LuxS, the enzyme that mediates AI-2 production, is defective in biofilm development in vitro. Transcriptomic analyses of biofilms formed by wild type (WT) and luxS mutant (luxS) strains revealed a downregulation of prophage loci in the luxS mutant biofilms compared to the WT. Detection of phages and eDNA within biofilms may suggest that DNA release by phage-mediated cell lysis contributes to C. difficile biofilm formation. In order to understand if LuxS mediates C. difficile crosstalk with other gut species, C. difficile interactions with a common gut bacterium, Bacteroides fragilis, were studied. We demonstrate that C. difficile growth is significantly reduced when co-cultured with B. fragilis in mixed biofilms. Interestingly, the absence of C. difficile LuxS alleviates the B. fragilis-mediated growth inhibition. Dual species RNA-sequencing analyses from single and mixed biofilms revealed differential modulation of distinct metabolic pathways for C. difficile WT, luxS and B. fragilis upon co-culture, indicating that AI-2 may be involved in induction of selective metabolic responses in B. fragilis. Overall, our data suggest that C. difficile LuxS/AI-2 utilises different mechanisms to mediate formation of single and mixed species communities.
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Affiliation(s)
- Ross T Slater
- University of Warwick, Gibbet Hill Road, Coventry, CV4 7AL, United Kingdom
| | - Lucy R Frost
- University of Warwick, Gibbet Hill Road, Coventry, CV4 7AL, United Kingdom
| | - Sian E Jossi
- University of Warwick, Gibbet Hill Road, Coventry, CV4 7AL, United Kingdom
| | - Andrew D Millard
- University of Leicester, University Road, Leicester, LE1 7RH, UK
| | - Meera Unnikrishnan
- University of Warwick, Gibbet Hill Road, Coventry, CV4 7AL, United Kingdom.
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8
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Unique Characteristics of Recombinant Hybrid Manganese Superoxide Dismutase from Staphylococcus equorum and S. saprophyticus. Protein J 2016; 35:136-44. [DOI: 10.1007/s10930-016-9650-5] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
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9
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Recent advances in optimal cell banking of mammalian cells for biopharmaceutical production. ACTA ACUST UNITED AC 2015. [DOI: 10.4155/pbp.14.46] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
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10
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Nehls U, Dietz S. Fungal aquaporins: cellular functions and ecophysiological perspectives. Appl Microbiol Biotechnol 2014; 98:8835-51. [PMID: 25213914 DOI: 10.1007/s00253-014-6049-0] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2014] [Revised: 08/13/2014] [Accepted: 08/15/2014] [Indexed: 12/21/2022]
Abstract
Three aspects have to be taken into consideration when discussing cellular water and solute permeability of fungal cells: cell wall properties, membrane permeability, and transport through proteinaceous pores (the main focus of this review). Yet, characterized major intrinsic proteins (MIPs) can be grouped into three functional categories: (mainly) water transporting aquaporins, aquaglyceroporins that confer preferentially solute permeability (e.g., glycerol and ammonia), and bifunctional aquaglyceroporins that can facilitate efficient water and solute transfer. Two ancestor proteins, a water (orthodox aquaporin) and a solute facilitator (aquaglyceroporin), are supposed to give rise to today's MIPs. Based on primary sequences of fungal MIPs, orthodox aquaporins/X-intrinsic proteins (XIPs) and FPS1-like/Yfl054-like/other aquaglyceroporins are supposed to be respective sister groups. However, at least within the fungal kingdom, no easy functional conclusion can be drawn from the phylogenetic position of a given protein within the MIP pedigree. In consequence, ecophysiological prediction of MIP relevance is not feasible without detailed functional analysis of the respective protein and expression studies. To illuminate the diverse MIP implications in fungal lifestyle, our current knowledge about protein function in two organisms, baker's yeast and the Basidiomycotic Laccaria bicolor, an ectomycorrhizal model fungus, was exemplarily summarized in this review. MIP function has been investigated in such a depth in Saccharomyces cerevisiae that a system-wide view is possible. Yeast lifestyle, however, is special in many circumstances. Therefore, L. bicolor as filamentous Basidiomycete was added and allows insight into a very different way of life. Special emphasis was laid in this review onto ecophysiological interpretation of MIP function.
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Affiliation(s)
- Uwe Nehls
- Botany, University of Bremen, Leobenerstr. 2, 28359, Bremen, Germany,
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11
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Pop OL, Brandau T, Schwinn J, Vodnar DC, Socaciu C. The influence of different polymers on viability of Bifidobacterium lactis 300b during encapsulation, freeze-drying and storage. Journal of Food Science and Technology 2014; 52:4146-55. [PMID: 26139879 DOI: 10.1007/s13197-014-1441-4] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Revised: 05/23/2014] [Accepted: 06/03/2014] [Indexed: 01/09/2023]
Abstract
Seven different types of natural polymers namely hydroxypropyl methylcellulose (HPMC), sodium-carboxymethyl cellulose (Na-CMC), microcrystalline cellulose (MCC), starch BR-07, starch BR-08, dextrin and pullulan were used in order to develop the optimal formula for the entrapment of Bifidobacterium lactis 300B in Ca-alginate based granules. Laminar flow drip casting with Brace-Encapsulator was used in order to prepare the granules. The results showed that alginate/pullulan and alginate/HPMC formulation provide high protection for the bacterial strain used for encapsulation. These two formulations were further used to obtain freeze dried granules, for which the viability in time and at different temperatures was tested. The final results showed a higher viability than the level of the therapeutic minimum (>10(7) CFU/g) after 15 days of storage. Other parameters like entrapment efficiency, production rate, sphericity, flowability were also discussed.
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Affiliation(s)
- Oana Lelia Pop
- Faculty of Food Science and Technology, University of Agricultural Sciences and Veterinary Medicine, 3-5 Manastur str., Cluj-Napoca, 400372 Romania
| | | | - Jens Schwinn
- Brace GmbH, Am Mittelberg 5, Karlstein am Main, D-63791 Germany
| | - Dan Cristian Vodnar
- Faculty of Food Science and Technology, University of Agricultural Sciences and Veterinary Medicine, 3-5 Manastur str., Cluj-Napoca, 400372 Romania
| | - Carmen Socaciu
- Faculty of Food Science and Technology, University of Agricultural Sciences and Veterinary Medicine, 3-5 Manastur str., Cluj-Napoca, 400372 Romania
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12
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Lalaymia I, Cranenbrouck S, Declerck S. Maintenance and preservation of ectomycorrhizal and arbuscular mycorrhizal fungi. MYCORRHIZA 2014; 24:323-337. [PMID: 24292254 DOI: 10.1007/s00572-013-0541-8] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/26/2013] [Accepted: 11/05/2013] [Indexed: 06/02/2023]
Abstract
Short- to long-term preservation of mycorrhizal fungi is essential for their in-depth study and, in the case of culture collections, for safeguarding their biodiversity. Many different maintenance/preservation methods have been developed in the last decades, from soil- and substrate-based maintenance to preservation methods that reduce (e.g., storage under water) or arrest (e.g., cryopreservation) growth and metabolism; all have advantages and disadvantages. In this review, the principal methods developed so far for ectomycorrhizal and arbuscular mycorrhizal fungi are reported and described given their distinct biology/ecology/evolutionary history. Factors that are the most important for their storage are presented and a protocol proposed which is applicable, although not generalizable, for the long-term preservation at ultra-low temperature of a large panel of these organisms. For ECM fungi, isolates should be grown on membranes or directly in cryovials until the late stationary growth phase. The recommended cryopreservation conditions are: a cryoprotectant of 10% glycerol, applied 1-2 h prior to cryopreservation, a slow cooling rate (1 °C min(-1)) until storage below -130 °C, and fast thawing by direct plunging in a water bath at 35-37 °C. For AMF, propagules (i.e., spores/colonized root pieces) isolated from cultures in the late or stationary phase of growth should be used and incorporated in a carrier (i.e., soil or alginate beads), preferably dried, before cryopreservation. For in vitro-cultured isolates, 0.5 M trehalose should be used as cryoprotectant, while isolates produced in vivo can be preserved in dried soil without cryoprotectant. A fast cryopreservation cooling rate should be used (direct immersion in liquid nitrogen or freezing at temperatures below -130 °C), as well as fast thawing by direct immersion in a water bath at 35 °C.
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Affiliation(s)
- Ismahen Lalaymia
- Earth and Life Institute, Applied Microbiology, Mycology, Université catholique de Louvain, Croix du Sud 2, bte L7.05.06, 1348, Louvain-la-Neuve, Belgium
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13
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Unprecedented cell-selection using ultra-quick freezing combined with aquaporin expression. PLoS One 2014; 9:e87644. [PMID: 24558371 PMCID: PMC3928110 DOI: 10.1371/journal.pone.0087644] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2013] [Accepted: 12/25/2013] [Indexed: 11/19/2022] Open
Abstract
Freezing is usually used for preservation and storage of biological samples; however, this process may have some adverse effects such as cell membrane damage. Aquaporin (AQP), a water channel protein, has been suggested to play some roles for cryopreservation although its molecular mechanism remains unclear. Here we show that membrane damage caused by ultra-quick freezing is rescued by the expression of AQP4. We next examine if the expression of AQP combined with ultra-quick freezing can be used to select cells efficiently under freezing conditions where most cells are died. CHO cells stably expressing AQP4 were exclusively selected from mixed cell cultures. Having identified the increased expression of AQP4 during ES cell differentiation into neuro-ectoderm using bioinformatics, we confirmed the improved survival of differentiated ES cells with AQP4 expression. Finally we show that CHO cells transiently transfected with Endothelin receptor A and Aqp4 were also selected and concentrated by multiple cycles of freezing/thawing, which was confirmed with calcium imaging in response to endothelin. Furthermore, we found that the expression of AQP enables a reduction in the amount of cryoprotectants for freezing, thereby decreasing osmotic stress and cellular toxicity. Taken together, we propose that this simple but efficient and safe method may be applicable to the selection of mammalian cells for applications in regenerative medicine as well as cell-based functional assays or drug screening protocols.
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14
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Sette LD, Pagnocca FC, Rodrigues A. Microbial culture collections as pillars for promoting fungal diversity, conservation and exploitation. Fungal Genet Biol 2013; 60:2-8. [PMID: 23872281 DOI: 10.1016/j.fgb.2013.07.004] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2013] [Revised: 06/05/2013] [Accepted: 07/08/2013] [Indexed: 10/26/2022]
Abstract
Fungi are a diverse group of organisms with an overall global number of 1.5M up to 3.3M species on Earth. Besides their ecological roles as decomposers, fungi are important in several aspects of applied research. Here, we review how culture collections may promote the knowledge on diversity, conservation and biotechnological exploitation of fungi. The impact of fungi diversity on biotechnological studies is discussed. We point out the major roles of microbial repositories, including fungal preservation, prospecting, identification, authentication and supply. A survey on the World Data Center for Microorganisms (WDCM) powered by the World Federation for Culture Collections and on the Genetic Heritage Management Council (CGEN) database revealed that 46 Brazilian culture collections registered in these databases are dedicate to preserving fungi. Most of these culture collections are located in the Southeast of Brazil. This scenario also demonstrates that Brazil has many collections focused on fungal strains, but the lack of up-to-date information in WDCM as well as of a solid national platform for culture collections registration do not allow accurate assessment of fungal preservation.
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Affiliation(s)
- Lara Durães Sette
- UNESP - São Paulo State University, Department of Biochemistry and Microbiology, Rio Claro, SP 13506-900, Brazil.
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15
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Clarke A, Morris GJ, Fonseca F, Murray BJ, Acton E, Price HC. A Low Temperature Limit for Life on Earth. PLoS One 2013; 8:e66207. [PMID: 23840425 PMCID: PMC3686811 DOI: 10.1371/journal.pone.0066207] [Citation(s) in RCA: 62] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2012] [Accepted: 05/06/2013] [Indexed: 12/29/2022] Open
Abstract
There is no generally accepted value for the lower temperature limit for life on Earth. We present empirical evidence that free-living microbial cells cooling in the presence of external ice will undergo freeze-induced desiccation and a glass transition (vitrification) at a temperature between −10°C and −26°C. In contrast to intracellular freezing, vitrification does not result in death and cells may survive very low temperatures once vitrified. The high internal viscosity following vitrification means that diffusion of oxygen and metabolites is slowed to such an extent that cellular metabolism ceases. The temperature range for intracellular vitrification makes this a process of fundamental ecological significance for free-living microbes. It is only where extracellular ice is not present that cells can continue to metabolise below these temperatures, and water droplets in clouds provide an important example of such a habitat. In multicellular organisms the cells are isolated from ice in the environment, and the major factor dictating how they respond to low temperature is the physical state of the extracellular fluid. Where this fluid freezes, then the cells will dehydrate and vitrify in a manner analogous to free-living microbes. Where the extracellular fluid undercools then cells can continue to metabolise, albeit slowly, to temperatures below the vitrification temperature of free-living microbes. Evidence suggests that these cells do also eventually vitrify, but at lower temperatures that may be below −50°C. Since cells must return to a fluid state to resume metabolism and complete their life cycle, and ice is almost universally present in environments at sub-zero temperatures, we propose that the vitrification temperature represents a general lower thermal limit to life on Earth, though its precise value differs between unicellular (typically above −20°C) and multicellular organisms (typically below −20°C). Few multicellular organisms can, however, complete their life cycle at temperatures below ∼−2°C.
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Affiliation(s)
- Andrew Clarke
- British Antarctic Survey, High Cross, Madingley Road, Cambridge, United Kingdom
- School of Environmental Sciences, University of East Anglia, Norwich, United Kingdom
- * E-mail:
| | - G. John Morris
- Asymptote Ltd, St John’s Innovation Centre, Cambridge, United Kingdom
| | - Fernanda Fonseca
- Institut National de la Recherche Agronomique, Thiverval Grignon, France
| | - Benjamin J. Murray
- School of Earth and Environment, University of Leeds, Leeds, United Kingdom
| | - Elizabeth Acton
- Asymptote Ltd, St John’s Innovation Centre, Cambridge, United Kingdom
| | - Hannah C. Price
- School of Earth and Environment, University of Leeds, Leeds, United Kingdom
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16
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Tashyreva D, Elster J. Production of Dormant Stages and Stress Resistance of Polar Cyanobacteria. ACTA ACUST UNITED AC 2012. [DOI: 10.1007/978-94-007-4966-5_21] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/20/2023]
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17
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Whiteford DC, Klingelhoets JJ, Bambenek MH, Dahl JL. Deletion of the histone-like protein (Hlp) from Mycobacterium smegmatis results in increased sensitivity to UV exposure, freezing and isoniazid. Microbiology (Reading) 2010; 157:327-335. [DOI: 10.1099/mic.0.045518-0] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
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18
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Pérez-Torrado R, Panadero J, Hernández-López MJ, Prieto JA, Randez-Gil F. Global expression studies in baker's yeast reveal target genes for the improvement of industrially-relevant traits: the cases of CAF16 and ORC2. Microb Cell Fact 2010; 9:56. [PMID: 20626860 PMCID: PMC2912791 DOI: 10.1186/1475-2859-9-56] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2010] [Accepted: 07/13/2010] [Indexed: 11/10/2022] Open
Abstract
Background Recent years have seen a huge growth in the market of industrial yeasts with the need for strains affording better performance or to be used in new applications. Stress tolerance of commercial Saccharomyces cerevisiae yeasts is, without doubt, a trait that needs improving. Such trait is, however, complex, and therefore only in-depth knowledge of their biochemical, physiological and genetic principles can help us to define improvement strategies and to identify the key factors for strain selection. Results We have determined the transcriptional response of commercial baker's yeast cells to both high-sucrose and lean dough by using DNA macroarrays and liquid dough (LD) model system. Cells from compressed yeast blocks display a reciprocal transcription program to that commonly reported for laboratory strains exposed to osmotic stress. This discrepancy likely reflects differences in strain background and/or experimental design. Quite remarkably, we also found that the transcriptional response of starved baker's yeast cells was qualitatively similar in the presence or absence of sucrose in the LD. Nevertheless, there was a set of differentially regulated genes, which might be relevant for cells to adapt to high osmolarity. Consistent with this, overexpression of CAF16 or ORC2, two transcriptional factor-encoding genes included in this group, had positive effects on leavening activity of baker's yeast. Moreover, these effects were more pronounced during freezing and frozen storage of high-sucrose LD. Conclusions Engineering of differentially regulated genes opens the possibility to improve the physiological behavior of baker's yeast cells under stress conditions like those encountered in downstream applications.
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Affiliation(s)
- Roberto Pérez-Torrado
- Department of Biotechnology, Instituto de Agroquímica y Tecnología de los Alimentos CSIC, PO Box 73, E-46100-Burjassot, Valencia, Spain
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19
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Bioprospecting for microbial products that affect ice crystal formation and growth. Appl Microbiol Biotechnol 2009; 85:481-9. [DOI: 10.1007/s00253-009-2291-2] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2009] [Revised: 10/01/2009] [Accepted: 10/03/2009] [Indexed: 10/20/2022]
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20
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Aguilera J, Andreu P, Randez-Gil F, Prieto JA. Adaptive evolution of baker's yeast in a dough-like environment enhances freeze and salinity tolerance. Microb Biotechnol 2009; 3:210-21. [PMID: 21255321 PMCID: PMC3836578 DOI: 10.1111/j.1751-7915.2009.00136.x] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
Abstract
We used adaptive evolution to improve freeze tolerance of industrial baker's yeast. Our hypothesis was that adaptation to low temperature is accompanied by enhanced resistance of yeast to freezing. Based on this hypothesis, yeast was propagated in a flour‐free liquid dough model system, which contained sorbitol and NaCl, by successive batch refreshments maintained constantly at 12°C over at least 200 generations. Relative to the parental population, the maximal growth rate (µmax) under the restrictive conditions, increased gradually over the time course of the experiment. This increase was accompanied by enhanced freeze tolerance. However, these changes were not the consequence of genetic adaptation to low temperature, a fact that was confirmed by prolonged selection of yeast cells in YPD at 12°C. Instead, the experimental populations showed a progressive increase in NaCl tolerance. This phenotype was likely achieved at the expense of others traits, since evolved cells showed a ploidy reduction, a defect in the glucose derepression mechanism and a loss in their ability to utilize gluconeogenic carbon sources. We discuss the genetic flexibility of S. cerevisiae in terms of adaptation to the multiple constraints of the experimental design applied to drive adaptive evolution and the technologically advantageous phenotype of the evolved population.
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Affiliation(s)
- Jaime Aguilera
- Department of Biotechnology, Instituto de Agroquímica y Tecnología de Alimentos, Consejo Superior de Investigaciones Científicas, Poligono de la Coma, s/n, PO Box 73. 46100-Burjassot, Valencia, Spain
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21
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Nakamura T, Takagi H, Shima J. Effects of ice-seeding temperature and intracellular trehalose contents on survival of frozen Saccharomyces cerevisiae cells. Cryobiology 2009; 58:170-4. [DOI: 10.1016/j.cryobiol.2008.11.012] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2008] [Revised: 11/25/2008] [Accepted: 11/28/2008] [Indexed: 11/28/2022]
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22
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Amato P, Christner BC. Energy metabolism response to low-temperature and frozen conditions in Psychrobacter cryohalolentis. Appl Environ Microbiol 2009; 75:711-8. [PMID: 19060163 PMCID: PMC2632129 DOI: 10.1128/aem.02193-08] [Citation(s) in RCA: 87] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2008] [Accepted: 11/29/2008] [Indexed: 12/21/2022] Open
Abstract
Studies of cold-active enzymes have provided basic information on the molecular and biochemical properties of psychrophiles; however, the physiological strategies that compensate for low-temperature metabolism remain poorly understood. We investigated the cellular pools of ATP and ADP in Psychrobacter cryohalolentis K5 incubated at eight temperatures between 22 degrees C and -80 degrees C. Cellular ATP and ADP concentrations increased with decreasing temperature, and the most significant increases were observed in cells that were incubated as frozen suspensions (<-5 degrees C). Respiratory uncoupling significantly decreased this temperature-dependent response, indicating that the proton motive force was required for energy adaptation to frozen conditions. Since ATP and ADP are key substrates in metabolic and energy conservation reactions, increasing their concentrations may provide a strategy for offsetting the kinetic temperature effect, thereby maintaining reaction rates at low temperature. The adenylate levels increased significantly <1 h after freezing and also when the cells were osmotically shocked to simulate the elevated solute concentrations encountered in the liquid fraction of the ice. Together, these data demonstrate that a substantial change in cellular energy metabolism is required for the cell to adapt to the low temperature and water activity conditions encountered during freezing. This physiological response may represent a critical biochemical compensation mechanism at low temperature, have relevance to cellular survival during freezing, and be important for the persistence of microorganisms in icy environments.
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Affiliation(s)
- Pierre Amato
- Louisiana State University, Department of Biological Sciences, Baton Rouge 70803, USA.
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23
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Phimolsiripol Y, Siripatrawan U, Tulyathan V, Cleland DJ. Effect of cold pre-treatment duration before freezing on frozen bread dough quality. Int J Food Sci Technol 2008. [DOI: 10.1111/j.1365-2621.2007.01685.x] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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24
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Rosell CM, Gómez M. Frozen Dough and Partially Baked Bread: An Update. FOOD REVIEWS INTERNATIONAL 2007. [DOI: 10.1080/87559120701418368] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
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25
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Soveral G, Veiga A, Loureiro-Dias MC, Tanghe A, Van Dijck P, Moura TF. Water channels are important for osmotic adjustments of yeast cells at low temperature. Microbiology (Reading) 2006; 152:1515-1521. [PMID: 16622068 DOI: 10.1099/mic.0.28679-0] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The importance of aquaporin expression in water permeability in Saccharomyces cerevisiae was assessed by measuring the osmotic water permeability coefficient (P
f) and the activation energies (E
a) from both hypo- and hypertonic experiments performed with whole protoplasts from four strains differing in aquaporin level of expression: parental, double-deleted and overexpressing AQY1 or AQY2. Double-deleted (lower P
f) and AQY1-overexpressing strains (higher P
f) presented linear Arrhenius plots with E
a consistent with fluxes mainly through the lipids [16·3 kcal mol−1 (68·2 kJ mol−1)] and with a strong contribution of channels [9·6 kcal mol−1 (40·2 kJ mol−1)], respectively. The Arrhenius plots for the parental (swelling experiments) and overexpressing AQY2 strains (swelling and shrinking experiments) were not linear, presenting a break point with a change in slope around 23 °C. The E
a values for these strains, calculated for temperatures ranging from 7 to 23 °C, were lower [9·5 kcal mol−1 (39·7 kJ mol−1)] than the values obtained from 23 to 38 °C [17 kcal mol−1 (71·1 kJ mol−1)]. This behaviour indicates that only in the lower temperature range did the water fluxes occur predominantly via the water channels. The permeabilities for each strain relative to the deletion strain show that an increase in permeability due to the presence of aquaporins was more relevant at low temperatures. Following our results, we propose that water channels play an important role for osmotic adjustment of yeast cells at low temperature.
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Affiliation(s)
- Graça Soveral
- Faculdade de Farmácia, Universidade de Lisboa, 1649-003 Lisboa, Portugal
- REQUIMTE, Dept Química, FCT-UNL, 2829-516 Caparica, Portugal
| | - Alexandra Veiga
- Centro de Engenharia Biológica, FC-UL, C2, 1749-016 Lisboa, Portugal
- Instituto Superior de Agronomia, 1349-017 Lisboa, Portugal
| | | | - An Tanghe
- Laboratory of Molecular Cell Biology, Institute of Botany and Microbiology, Katholieke Universiteit Leuven and Department of Molecular Microbiology, Flanders Interuniversity Institute for Biotechnology (VIB), Kasteelpark Arenberg 31, B-3001 Leuven-Heverlee, Flanders, Belgium
| | - Patrick Van Dijck
- Laboratory of Molecular Cell Biology, Institute of Botany and Microbiology, Katholieke Universiteit Leuven and Department of Molecular Microbiology, Flanders Interuniversity Institute for Biotechnology (VIB), Kasteelpark Arenberg 31, B-3001 Leuven-Heverlee, Flanders, Belgium
| | - Teresa F Moura
- REQUIMTE, Dept Química, FCT-UNL, 2829-516 Caparica, Portugal
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26
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Tanghe A, Van Dijck P, Thevelein JM. Why do microorganisms have aquaporins? Trends Microbiol 2006; 14:78-85. [PMID: 16406529 DOI: 10.1016/j.tim.2005.12.001] [Citation(s) in RCA: 86] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2005] [Revised: 11/16/2005] [Accepted: 12/13/2005] [Indexed: 10/25/2022]
Abstract
Aquaporins are channel proteins that enhance the permeability of cell membranes for water. They have been found in Bacteria, Archaea and Eukaryotes. However, their absence in many microorganisms suggests that aquaporins do not fulfill a broad role such as turgor regulation or osmoadaptation but, instead, fulfill a role that enables microorganisms to have specific lifestyles. The recent discovery that aquaporins enhance cellular tolerance against rapid freezing suggests that they have ecological relevance. We have identified several examples of large-scale freeze-thawing of microbes in nature and we also draw attention to alternative lifestyle-related functions for aquaporins, which will be a focus of future research.
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Affiliation(s)
- An Tanghe
- Laboratory of Molecular Cell Biology, Institute of Botany and Microbiology, Katholieke Universiteit Leuven and Flanders Interuniversity Institute for Biotechnology (VIB), Kasteelpark Arenberg 31, B-3001 Leuven-Heverlee, Flanders, Belgium
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27
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Jin Y, Weining S, Nevo E. A MAPK gene from Dead Sea fungus confers stress tolerance to lithium salt and freezing-thawing: Prospects for saline agriculture. Proc Natl Acad Sci U S A 2005; 102:18992-7. [PMID: 16365289 PMCID: PMC1323214 DOI: 10.1073/pnas.0509653102] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The Dead Sea is one of the most saline lakes on earth ( approximately 340 g/liter salinity) and is approximately 10 times saltier than the oceans. Eurotium herbariorum, a common fungal species, was isolated from its water. EhHOG gene, encoding a mitogen-activated protein kinase (MAPK) that plays an essential role in the osmoregulatory pathway in yeast and many other eukaryotes, was isolated from E. herbariorum. The deduced amino acid sequences of EhHOG indicated high similarity with homologous genes from Aspergillus nidulans, Saccharomyces cerevisiae, and Schizosaccharomyces pombe and contained a TGY motif for phosphorylation by MAPK kinase. When EhHOG was expressed in S. cerevisiae hog1Delta mutant, the growth and aberrant morphology of hog1Delta mutant was restored under high osmotic stress condition. Moreover, intracellular glycerol content in the transformant increased to a much higher level than that in the mutant during salt-stress situations. hog1Delta mutant complemented by EhHOG outperformed the wild type or had higher genetic fitness under high Li(+) and freezing-thawing conditions. The present study revealed the putative presence of a high-osmolarity glycerol response (HOG) pathway in E. herbariorum and the significance of EhHOG in osmotic regulation, heat stress, freeze stress, and oxidative stress. The Dead Sea is becoming increasingly more saline while the fungi living in it evolutionarily adapt to its high-saline environment, particularly with the extraordinarily high Li(+) concentration. The Dead Sea is potentially an excellent model for studies of evolution under extreme environments and is an important gene pool for future agricultural genetic engineering prospects.
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Affiliation(s)
- Yan Jin
- Institute of Evolution, University of Haifa, Haifa 31905, Israel
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28
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Stockwell VO, Loper JE. The sigma factor RpoS is required for stress tolerance and environmental fitness of Pseudomonas fluorescens Pf-5. Microbiology (Reading) 2005; 151:3001-3009. [PMID: 16151210 DOI: 10.1099/mic.0.28077-0] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Many micro-organisms exist in natural habitats that are subject to severe or dramatically fluctuating environmental conditions. Such is the case for bacteria inhabiting plant surfaces, where they are exposed to UV irradiation, oxygen radicals, and large fluctuations in temperature and moisture. This study focuses on the role of RpoS, a central regulator of stationary-phase gene expression in bacterial cells, in stress response and environmental fitness of Pseudomonas fluorescens Pf-5. Strain Pf-5 is a rhizosphere-inhabiting bacterium that suppresses plant diseases caused by several plant-pathogenic fungi and oomycetes. Previous studies demonstrated that rpoS was required for osmotic and oxidative stress resistance of Pf-5. The results of this study demonstrate a role for rpoS in tolerance of Pf-5 to freezing, starvation, UV irradiation and desiccation stress. In field studies, an rpoS mutant was compromised in rhizosphere colonization of plants in dry soil, whereas similar rhizosphere populations were established by Pf-5 and an rpoS mutant in well-irrigated soils. RpoS is a key determinant in stress response and environmental fitness of the rhizosphere bacterium P. fluorescens Pf-5.
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Affiliation(s)
- Virginia O Stockwell
- Department of Botany and Plant Pathology, Oregon State University, Corvallis, OR 97331, USA
| | - Joyce E Loper
- United States Department of Agriculture, Agricultural Research Service, Horticultural Crops Research Laboratory, 3420 NW Orchard Avenue, Corvallis, OR 97330, USA
- Department of Botany and Plant Pathology, Oregon State University, Corvallis, OR 97331, USA
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Tanghe A, Van Dijck P, Colavizza D, Thevelein JM. Aquaporin-mediated improvement of freeze tolerance of Saccharomyces cerevisiae is restricted to rapid freezing conditions. Appl Environ Microbiol 2004; 70:3377-82. [PMID: 15184134 PMCID: PMC427737 DOI: 10.1128/aem.70.6.3377-3382.2004] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Previous observations that aquaporin overexpression increases the freeze tolerance of baker's yeast (Saccharomyces cerevisiae) without negatively affecting the growth or fermentation characteristics held promise for the development of commercial baker's yeast strains used in frozen dough applications. In this study we found that overexpression of the aquaporin-encoding genes AQY1-1 and AQY2-1 improves the freeze tolerance of industrial strain AT25, but only in small doughs under laboratory conditions and not in large doughs under industrial conditions. We found that the difference in the freezing rate is apparently responsible for the difference in the results. We tested six different cooling rates and found that at high cooling rates aquaporin overexpression significantly improved the survival of yeast cells, while at low cooling rates there was no significant effect. Differences in the cultivation conditions and in the thawing rate did not influence the freeze tolerance under the conditions tested. Survival after freezing is determined mainly by two factors, cellular dehydration and intracellular ice crystal formation, which depend in an inverse manner on the cooling velocity. In accordance with this so-called two-factor hypothesis of freezing injury, we suggest that water permeability is limiting, and therefore that aquaporin function is advantageous, only under rapid freezing conditions. If this hypothesis is correct, then aquaporin overexpression is not expected to affect the leavening capacity of yeast cells in large, industrial frozen doughs, which do not freeze rapidly. Our results imply that aquaporin-overexpressing strains have less potential for use in frozen doughs than originally thought.
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Affiliation(s)
- An Tanghe
- Laboratorium voor Moleculaire Celbiologie and Vlaams Interuniversitair Instituut voor Biotechnologie, Institute of Botany and Microbiology, Katholieke Universiteit Leuven, B-3001 Leuven-Heverlee, Flanders, Belgium
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