1
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Zhang D, Tong D, Wang Z, Wang S, Jia Y, Ning Y. Inactivation mechanism of phenyllactic acid against Bacillus cereus spores and its application in milk beverage. Food Chem 2024; 453:139601. [PMID: 38754350 DOI: 10.1016/j.foodchem.2024.139601] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2023] [Revised: 05/06/2024] [Accepted: 05/07/2024] [Indexed: 05/18/2024]
Abstract
Phenyllactic acid (PLA) as a natural phenolic acid exhibits antibacterial activity against non-spore-forming bacteria, while the inhibitory effect against bacterial spore remained unknown. Herein, this study investigated the inactivation effect of PLA against Bacillus cereus spores. The results revealed that the minimum inhibitory concentration of PLA was 1.25 mg/mL. PLA inhibited the outgrowth of germinated spores into vegetative cells rather than germination of spores. PLA disrupted the spore coat, and damaged the permeability and integrity of inner membrane. Moreover, PLA disturbed the establishment of membrane potential due to the inhibition of oxidative metabolism. SEM observations further visualized the morphological changes and structural disruption caused by PLA. Besides, PLA caused the degradation of DNA of germinated spores. Finally, PLA was applied in milk beverage, and showed promising inhibitory effect against B. cereus spores. This finding could provide scientific basis for the application of PLA against spore-forming bacteria in food industry.
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Affiliation(s)
- Dongchun Zhang
- College of Food and Biology, Hebei University of Science and Technology, Shijiazhuang 050018, China
| | - Danya Tong
- College of Food and Biology, Hebei University of Science and Technology, Shijiazhuang 050018, China
| | - Zhixin Wang
- College of Food and Biology, Hebei University of Science and Technology, Shijiazhuang 050018, China
| | - Shijie Wang
- College of Food and Biology, Hebei University of Science and Technology, Shijiazhuang 050018, China
| | - Yingmin Jia
- Beijing Advanced Innovation Center for Food Nutrition and Human Health, Beijing Technology and Business University, Beijing 100048, China
| | - Yawei Ning
- College of Food and Biology, Hebei University of Science and Technology, Shijiazhuang 050018, China.
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2
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Trunet C, Vischer N, Coroller L, Brul S. Germination and outgrowth of Bacillus mycoides KBAB4 spores are impacted by environmental pH, quantitatively analyzed at single cell level with sporetracker. Food Microbiol 2024; 121:104509. [PMID: 38637073 DOI: 10.1016/j.fm.2024.104509] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2023] [Revised: 02/06/2024] [Accepted: 02/24/2024] [Indexed: 04/20/2024]
Abstract
Quantifying spore germination and outgrowth heterogeneity is challenging. Single cell level analysis should provide supplementary knowledge regarding the impact of unfavorable conditions on germination and outgrowth dynamics. This work aimed to quantify the impact of pH on spore germination and outgrowth, investigating the behavior of individual spore crops, produced under optimal and suboptimal conditions. Bacillus mycoides (formerly B. weihenstephanensis) KBAB4 spores, produced at pH 7.4 and at pH 5.5 were incubated at different pH values, from pH 5.2 to 7.4. The spores were monitored by microscopy live imaging, in controlled conditions, at 30 °C. The images were analyzed using SporeTracker, to determine the state of single cells. The impact of pH on germination and outgrowth times and rates was estimated and the correlation between these parameters was quantified. The correlation between germination and outgrowth times was significantly higher at low pH. These results suggest that an environmental pressure highlights the heterogeneity of spore germination and outgrowth within a spore population. Results were consistent with previous observations at population level, now confirmed and extended to single cell level. Therefore, single cell level analyses can be used to quantify the heterogeneity of spore populations, which is of interest in order to control the development of spore-forming bacteria, responsible for food safety issues.
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Affiliation(s)
- C Trunet
- Univ Brest, INRAE, Laboratoire Universitaire de Biodiversité et Écologie Microbienne, F-29000, Quimper, France.
| | - N Vischer
- Laboratory for Molecular Biology and Microbial Food Safety, University of Amsterdam, Science Park 904, 1098 XH, Amsterdam, the Netherlands
| | - L Coroller
- Univ Brest, INRAE, Laboratoire Universitaire de Biodiversité et Écologie Microbienne, F-29000, Quimper, France
| | - S Brul
- Laboratory for Molecular Biology and Microbial Food Safety, University of Amsterdam, Science Park 904, 1098 XH, Amsterdam, the Netherlands
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3
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Saraiva GD, Maia JR, Lima JA, Nogueira CES, Freire PTC, de Sousa FF, Teixeira AMR, Mendes Filho J. Pressure induced transformations in sorbic acid. SPECTROCHIMICA ACTA. PART A, MOLECULAR AND BIOMOLECULAR SPECTROSCOPY 2017; 184:327-334. [PMID: 28528253 DOI: 10.1016/j.saa.2017.05.019] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/12/2016] [Revised: 04/18/2017] [Accepted: 05/09/2017] [Indexed: 06/07/2023]
Abstract
This research reports a pressure dependent Raman study of the sorbic acid between 0.0 and 10.0GPa. The unpolarized Raman spectra were measured in the spectral range of 20-3000cm-1. The high-pressure Raman scattering study of the sorbic acid showed that it underwent a gradual, disordering process. At the room temperature and at the ambient pressure conditions, the crystal structure of the sorbic acid belongs to the monoclinic system with a C2/c (C2h6) space group. The pressure increase induced a higher disorder in the monoclinic unit cell, since a single bending mode, and only very broad stretching Raman modes are present at pressure of ~10GPa. Upon pressure release the high-pressure phase transforms directly into the ambient-pressure phase. The presence of the internal vibrational modes is a guarantee that the molecular structure is maintained. Beyond this, the presence of external modes shows that the crystal has a memory to reverse the process and suggest that the crystal, which was in high disorder (broad Raman bands), does not suffer decomposition in the crystalline structure. The DFT calculations for the sorbic acid were performed in order to understand the vibrational properties. The theoretical study showed that the volume of the unit cell and beta angle decrease significatively when passing from the 0.0GPa to 8.0GPa. The decreases in the volume and beta angle of this particular unit cell were supposed to induce the larger increase in the bandwidths of the observed bands, pointing to some disorder in the monoclinic phase.
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Affiliation(s)
- G D Saraiva
- Faculdade de Educação Ciências e Letras do Sertão Central, Universidade Estadual do Ceará, CEP 63.900-000, Quixadá, CE, Brazil.
| | - J R Maia
- Faculdade de Filosofia Dom Aureliano Mattos, Universidade Estadual do Ceará, CEP 63.900-000, Limoeiro do Norte, CE, Brazil
| | - J A Lima
- Departamento de Física, Universidade Federal do Ceará, Caixa Postal 6030, CEP 60455-760, Fortaleza-CE, Brazil
| | - C E S Nogueira
- Departamento de Física, Universidade Regional do Cariri, Juazeiro do Norte - CE, CEP 63040-005, Brazil
| | - P T C Freire
- Departamento de Física, Universidade Federal do Ceará, Caixa Postal 6030, CEP 60455-760, Fortaleza-CE, Brazil
| | - F F de Sousa
- Instituto de Ciências Exatas, Universidade Federal do Sul e Sudeste do Pará, CEP 68.505-080, Marabá, PA, Brazil
| | - A M R Teixeira
- Departamento de Física, Universidade Regional do Cariri, Juazeiro do Norte - CE, CEP 63040-005, Brazil
| | - J Mendes Filho
- Departamento de Física, Universidade Federal do Ceará, Caixa Postal 6030, CEP 60455-760, Fortaleza-CE, Brazil
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4
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Inhibition of nutrient- and high pressure-induced germination of Bacillus cereus spores by plant essential oils. INNOV FOOD SCI EMERG 2016. [DOI: 10.1016/j.ifset.2016.02.011] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
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5
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Wells-Bennik MH, Eijlander RT, den Besten HM, Berendsen EM, Warda AK, Krawczyk AO, Nierop Groot MN, Xiao Y, Zwietering MH, Kuipers OP, Abee T. Bacterial Spores in Food: Survival, Emergence, and Outgrowth. Annu Rev Food Sci Technol 2016; 7:457-82. [DOI: 10.1146/annurev-food-041715-033144] [Citation(s) in RCA: 87] [Impact Index Per Article: 10.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- Marjon H.J. Wells-Bennik
- TI Food and Nutrition, 6700 AN Wageningen, The Netherlands
- NIZO Food Research, 6718 ZB Ede, The Netherlands;
| | - Robyn T. Eijlander
- TI Food and Nutrition, 6700 AN Wageningen, The Netherlands
- NIZO Food Research, 6718 ZB Ede, The Netherlands;
| | - Heidy M.W. den Besten
- TI Food and Nutrition, 6700 AN Wageningen, The Netherlands
- Laboratory of Food Microbiology, Wageningen University, 6700 AA Wageningen, The Netherlands
| | - Erwin M. Berendsen
- TI Food and Nutrition, 6700 AN Wageningen, The Netherlands
- NIZO Food Research, 6718 ZB Ede, The Netherlands;
- Molecular Genetics Department, University of Groningen, 9700 AB Groningen, The Netherlands
| | - Alicja K. Warda
- TI Food and Nutrition, 6700 AN Wageningen, The Netherlands
- Laboratory of Food Microbiology, Wageningen University, 6700 AA Wageningen, The Netherlands
- Wageningen UR Food & Biobased Research, 6700 AA Wageningen, The Netherlands
| | - Antonina O. Krawczyk
- TI Food and Nutrition, 6700 AN Wageningen, The Netherlands
- Molecular Genetics Department, University of Groningen, 9700 AB Groningen, The Netherlands
| | - Masja N. Nierop Groot
- TI Food and Nutrition, 6700 AN Wageningen, The Netherlands
- Wageningen UR Food & Biobased Research, 6700 AA Wageningen, The Netherlands
| | - Yinghua Xiao
- TI Food and Nutrition, 6700 AN Wageningen, The Netherlands
- Laboratory of Food Microbiology, Wageningen University, 6700 AA Wageningen, The Netherlands
| | - Marcel H. Zwietering
- TI Food and Nutrition, 6700 AN Wageningen, The Netherlands
- Laboratory of Food Microbiology, Wageningen University, 6700 AA Wageningen, The Netherlands
| | - Oscar P. Kuipers
- TI Food and Nutrition, 6700 AN Wageningen, The Netherlands
- Molecular Genetics Department, University of Groningen, 9700 AB Groningen, The Netherlands
| | - Tjakko Abee
- TI Food and Nutrition, 6700 AN Wageningen, The Netherlands
- Laboratory of Food Microbiology, Wageningen University, 6700 AA Wageningen, The Netherlands
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6
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Pandey R, Pieper GH, Beek AT, Vischer NO, Smelt JP, Manders EM, Brul S. Quantifying the effect of sorbic acid, heat and combination of both on germination and outgrowth of Bacillus subtilis spores at single cell resolution. Food Microbiol 2015; 52:88-96. [DOI: 10.1016/j.fm.2015.06.007] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/04/2015] [Revised: 05/10/2015] [Accepted: 06/19/2015] [Indexed: 11/26/2022]
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7
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Saraiva GD, Nogueira CES, Freire PTC, de Sousa FF, da Silva JH, Teixeira AMR, Mendes Filho J. Temperature-dependent vibrational spectroscopic study and DFT calculations of the sorbic acid. SPECTROCHIMICA ACTA. PART A, MOLECULAR AND BIOMOLECULAR SPECTROSCOPY 2015; 137:1409-1416. [PMID: 25310262 DOI: 10.1016/j.saa.2014.08.142] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/25/2014] [Revised: 07/05/2014] [Accepted: 08/31/2014] [Indexed: 06/04/2023]
Abstract
This work reports a temperature-dependent vibrational spectroscopic study of the sorbic acid (C6H8O2), as well as the mode assignment at ambient conditions, based on the density functional theory. Temperature-dependent vibrational properties have been performed in polycrystalline sorbic acid through both Raman and infrared spectroscopy in the 20-300 K and 80-300 K temperature ranges, respectively. These studies present the occurrence of some modifications in the Raman spectra that could be interpreted as a low temperature phase transition undergone by sorbic acid from the monoclinic phase to an unknown phase with conformational change of the molecules in the unit cell.
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Affiliation(s)
- G D Saraiva
- Faculdade de Educação Ciências e Letras do Sertão Central, Universidade Estadual do Ceará, CEP 63.900-000, Quixadá, CE Brazil.
| | - C E S Nogueira
- Departamento de Física, Universidade Regional do Cariri, Crato, CE 63010-970, Brazil
| | - P T C Freire
- Departamento de Física, Universidade Federal do Ceará, Caixa Postal 6030, CEP 60455-760, Fortaleza, CE Brazil
| | - F F de Sousa
- Instituto de Ciências Exatas, Universidade Federal do Sul e Sudeste do Pará, CEP 68.505-080, Marabá, PA Brazil
| | - J H da Silva
- Universidade Federal do Cariri, 63000-000 Juazeiro do Norte, CE, Brazil
| | - A M R Teixeira
- Departamento de Física, Universidade Regional do Cariri, Crato, CE 63010-970, Brazil
| | - J Mendes Filho
- Departamento de Física, Universidade Federal do Ceará, Caixa Postal 6030, CEP 60455-760, Fortaleza, CE Brazil
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8
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Warda AK, den Besten HMW, Sha N, Abee T, Nierop Groot MN. Influence of food matrix on outgrowth heterogeneity of heat damaged Bacillus cereus spores. Int J Food Microbiol 2015; 201:27-34. [PMID: 25727186 DOI: 10.1016/j.ijfoodmicro.2015.02.010] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2014] [Revised: 01/20/2015] [Accepted: 02/02/2015] [Indexed: 11/26/2022]
Abstract
Spoilage of heat treated foods can be caused by the presence of surviving spore-formers. It is virtually impossible to prevent contamination at the primary production level as spores are ubiquitous present in the environment and can contaminate raw products. As a result spore inactivation treatments are widely used by food producing industries to reduce the microbial spore loads. However consumers prefer mildly processed products that have less impact on its quality and this trend steers industry towards milder preservation treatments. Such treatments may result in damaged instead of inactivated spores, and these spores may germinate, repair, and grow out, possibly leading to quality and safety issues. The ability to repair and grow out is influenced by the properties of the food matrix. In the current communication we studied the outgrowth from heat damaged Bacillus cereus ATCC 14579 spores on Anopore membrane, which allowed following outgrowth heterogeneity of individual spores on broccoli and rice-based media as well as standard and mildly acidified (pH 5.5) meat-based BHI. Rice, broccoli and BHI pH 5.5 media resulted in delayed outgrowth from untreated spores, and increased heterogeneity compared to BHI pH 7.4, with the most pronounced effect in rice media. Exposure to wet heat for 1 min at 95 °C caused 2 log inactivation and approximately 95% of the spores in the surviving fraction were damaged resulting in substantial delay in outgrowth based on the time required to reach a maximum microcolony size of 256 cells. The delay was most pronounced for heat-treated spores on broccoli medium followed by spores on rice media (both untreated and treated). Interestingly, the increase in outgrowth heterogeneity of heat treated spores on BHI pH 7.4 was more pronounced than on rice, broccoli and BHI pH 5.5 conceivably reflecting that conditions in BHI pH 7.4 better support spore damage repair. This study compares the effects of three main factors, namely heat treatment, pH of BHI and the effect of food matrix highlighting the impact of different (model) food recovery media on outgrowth efficiency and heterogeneity of non-heat-treated and heat-damaged B. cereus spores.
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Affiliation(s)
- Alicja K Warda
- TI Food and Nutrition, Wageningen, The Netherlands; Laboratory of Food Microbiology, Wageningen University, Wageningen, The Netherlands; Food & Biobased Research, Wageningen UR, Wageningen, The Netherlands
| | - Heidy M W den Besten
- Laboratory of Food Microbiology, Wageningen University, Wageningen, The Netherlands
| | - Na Sha
- Laboratory of Food Microbiology, Wageningen University, Wageningen, The Netherlands
| | - Tjakko Abee
- TI Food and Nutrition, Wageningen, The Netherlands; Laboratory of Food Microbiology, Wageningen University, Wageningen, The Netherlands.
| | - Masja N Nierop Groot
- TI Food and Nutrition, Wageningen, The Netherlands; Food & Biobased Research, Wageningen UR, Wageningen, The Netherlands
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9
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Alnoman M, Udompijitkul P, Paredes-Sabja D, Sarker MR. The inhibitory effects of sorbate and benzoate against Clostridium perfringens type A isolates. Food Microbiol 2014; 48:89-98. [PMID: 25790996 DOI: 10.1016/j.fm.2014.12.007] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2014] [Revised: 12/02/2014] [Accepted: 12/03/2014] [Indexed: 11/30/2022]
Abstract
This study evaluated the inhibitory effects of sorbate and benzoate against Clostridium perfringens type A food poisoning (FP) and non-food-borne (NFB) disease isolates. No significant inhibition of germination of spores of both FP and NFB isolates was observed in rich medium (pH 7.0) supplemented with permissive level of sodium sorbate (0.3% ≈ 0.13 mM undissociated sorbic acid) or sodium benzoate (0.1% ≈ 0.01 mM undissociated benzoic acid) used in foods. However, these levels of sorbate and benzoate effectively arrested outgrowth of germinated C. perfringens spores in rich medium. Lowering the pH of the medium increases the inhibitory effects of sorbate and benzoate against germination of spores of NFB isolates, and outgrowth of spores of both FP and NFB isolates. Furthermore, sorbate and benzoate inhibited vegetative growth of C. perfringens isolates. However, the permissible levels of these organic salts could not control the growth of C. perfringens spores in chicken meat stored under extremely abusive conditions. In summary, although sorbate and benzoate showed inhibitory activities against C. perfringens in the rich medium, no such effect was observed in cooked chicken meat. Therefore, caution should be taken when applying these organic salts into meat products to reduce or eliminate C. perfringens spores.
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Affiliation(s)
- Maryam Alnoman
- Department of Biomedical Sciences, College of Veterinary Medicine, Oregon State University, Corvallis, OR, 97331, USA
| | - Pathima Udompijitkul
- Department of Food Science and Technology, Faculty of Agro-Industry, Kasetsart University, Bangkok, Thailand
| | - Daniel Paredes-Sabja
- Department of Biomedical Sciences, College of Veterinary Medicine, Oregon State University, Corvallis, OR, 97331, USA; Laboratorio de Mecanismos de Patogénesis Bacteriana, Departamento de Ciencias Biológicas, Facultad de Ciencias Biológicas, Universidad Andrés Bello, Santiago, Chile
| | - Mahfuzur R Sarker
- Department of Biomedical Sciences, College of Veterinary Medicine, Oregon State University, Corvallis, OR, 97331, USA; Department of Microbiology, College of Science, Oregon State University, Corvallis, OR, 97331, USA.
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van Melis CCJ, den Besten HMW, Nierop Groot MN, Abee T. Quantification of the impact of single and multiple mild stresses on outgrowth heterogeneity of Bacillus cereus spores. Int J Food Microbiol 2014; 177:57-62. [PMID: 24607860 DOI: 10.1016/j.ijfoodmicro.2014.02.015] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2013] [Revised: 02/13/2014] [Accepted: 02/17/2014] [Indexed: 11/19/2022]
Abstract
Outgrowth heterogeneity of bacterial spore populations complicates both prediction and efficient control of spore outgrowth. In this study, the impact of mild preservation stresses on outgrowth of Bacillus cereus ATCC 14579 spores was quantified during the first stages of outgrowth. Heterogeneity in outgrowth of heat-treated (90°C for 10 min) and non-heat-treated germinated single spores to the maximum micro-colony stage of 256 cells was assessed by direct imaging on Anopore strips, placed on BHI plates at pH7 and pH5.5, without and with added NaCl or sorbic acid (HSA). At pH7 non-heated and heat-treated germinated spores required 6h to reach the maximum microcolony stage with limited heterogeneity, and these parameters were only slightly affected with both types of spores when incubated at pH7 with added NaCl. Notably, the most pronounced effects were observed during outgrowth of spores at pH5.5 without and with added NaCl or HSA. Non-heat-treated germinated spores showed again efficient outgrowth with limited heterogeneity reaching the maximum microcolony stage after 6h at pH5.5, which increased to 12h and 16 h with added NaCl and HSA, respectively. In contrast, heat-treated spores displayed a strong delay between initial germination and swelling and further outgrowth at pH5.5, resulting in large heterogeneity and low numbers of fastest growers reaching the maximum microcolony stage after 10, 12 and 24h, without and with added NaCl or HSA, respectively. This work shows that Anopore technology provides quantitative information on the impact of combined preservation stresses on outgrowth of single spores, showing that outgrowth of germinated heat-treated spores is significantly affected at pH5.5 with a large fraction of spores arrested in the early outgrowth stage, and with outgrowing cells showing large heterogeneity with only a small fraction committed to relatively fast outgrowth.
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Affiliation(s)
- C C J van Melis
- Top Institute Food and Nutrition, Nieuwe Kanaal 9A, 6709 PA, Wageningen, The Netherlands; Food Microbiology Laboratory, Wageningen University, Bornse Weilanden 9, 6708 WG, Wageningen, The Netherlands
| | - H M W den Besten
- Food Microbiology Laboratory, Wageningen University, Bornse Weilanden 9, 6708 WG, Wageningen, The Netherlands
| | - M N Nierop Groot
- Top Institute Food and Nutrition, Nieuwe Kanaal 9A, 6709 PA, Wageningen, The Netherlands; Food and Biobased Research, Wageningen University & Research Centre, Bornse Weilanden 9, 6708 WG, Wageningen, The Netherlands
| | - T Abee
- Top Institute Food and Nutrition, Nieuwe Kanaal 9A, 6709 PA, Wageningen, The Netherlands; Food Microbiology Laboratory, Wageningen University, Bornse Weilanden 9, 6708 WG, Wageningen, The Netherlands.
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11
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Live-cell imaging tool optimization to study gene expression levels and dynamics in single cells of Bacillus cereus. Appl Environ Microbiol 2013; 79:5643-51. [PMID: 23851094 DOI: 10.1128/aem.01347-13] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Single-cell methods are a powerful application in microbial research to study the molecular mechanism underlying phenotypic heterogeneity and cell-to-cell variability. Here, we describe the optimization and application of single-cell time-lapse fluorescence microscopy for the food spoilage bacterium Bacillus cereus specifically. This technique is useful to study cellular development and adaptation, gene expression, protein localization, protein mobility, and cell-to-cell communication over time at the single-cell level. By adjusting existing protocols, we have enabled the visualization of growth and development of single B. cereus cells within a microcolony over time. Additionally, several different fluorescent reporter proteins were tested in order to select the most suitable green fluorescent protein (GFP) and red fluorescent protein (RFP) candidates for visualization of growth stage- and cell compartment-specific gene expression in B. cereus. With a case study concerning cotD expression during sporulation, we demonstrate the applicability of time-lapse fluorescence microscopy. It enables the assessment of gene expression levels, dynamics, and heterogeneity at the single-cell level. We show that cotD is not heterogeneously expressed among cells of a subpopulation. Furthermore, we discourage using plasmid-based reporter fusions for such studies, due to an introduced heterogeneity through copy number differences. This stresses the importance of using single-copy integrated reporter fusions for single-cell studies.
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