RESUMO
Four Gram-negative, facultative anaerobic, oxidase-negative and catalase-positive strains were isolated from lettuce sample collected from test beds at the National Institute of Agricultural Sciences in Wanju, South Korea. The whole genome sequences of the strains ranged from 4,624,629 to 4,849,846 bp in size, with DNA G + C contents of 54.32 to 54.56 mol%. Phylogenetic analyses based on 16S rRNA gene and four housekeeping (atpD, gyrB, infB, and rpoB) gene sequences showed that the four strains clustered closely together with Scandinavium type strains within the Enterobacteriaceae family. Moreover, the average nucleotide identity and digital DNA-DNA hybridization value of the proposed type strain (V105_6T) with the closely related Scandinavium type strains were in the range of 85.71-86.16% and 30.2-31.2%, respectively, which were all below the species delineation threshold values. The major cellular fatty acid of V105_6T was C16:0. Growth was observed at 7, 10 and 35 °C, and in the presence of 7% NaCl concentration. Based on phenotypic and genotypic results, strain V105_6T represents a novel species of the genus Scandinavium, for which the name Scandinavium lactucae sp. nov. is proposed. The type strain is V105_6T (= LMG 33389T = DSM 117134T).
Assuntos
Composição de Bases , DNA Bacteriano , Ácidos Graxos , Lactuca , Filogenia , RNA Ribossômico 16S , República da Coreia , Lactuca/microbiologia , RNA Ribossômico 16S/genética , DNA Bacteriano/genética , Ácidos Graxos/análise , Técnicas de Tipagem Bacteriana , Enterobacteriaceae/genética , Enterobacteriaceae/isolamento & purificação , Enterobacteriaceae/classificação , Hibridização de Ácido Nucleico , Genoma Bacteriano , Análise de Sequência de DNARESUMO
The Gram-negative, oxidase-negative, catalase-positive, rod-shaped strain Arafor3T was isolated from forest soil (France). Comparative 16S rRNA gene analysis and phylogenetic analysis based on (1) multilocus sequence analysis (MLSA) with four housekeeping genes (atpD, gyrB, infB and rpoB) and (2) genomes indicated that strain Arafor3T shared 98.83% 16S rRNA gene sequence similarity with the type strain of Serratia fonticola DSM 4576T and was closely related to this same strain in the MLSA and in the phylogenomic tree reconstruction. Average nucleotide identity (ANI) and digital DNA-DNA hybridization (dDDH) comparisons of strain Arafor3T with its nearest neighbor S. fonticola DSM 4576T showed 93.5% identity and 55.7% sequence similarity, respectively, and were lower than the 96% and 70% species-level cut-off values relating to these analyses (Logan et al. in Int J Syst Evol Microbiol 59:2114-21, 2009, https://doi.org/10.1099/ijs.0.013649-0 ). The strain differed from S. fonticola in that it was urease and arginine dihydrolase negative. The major fatty acids of strain Arafor3T are C16:0, C16:1 ω7c/C16:1 ω6c, C14:0, C14:0 3-OH/16:1 isoI, and C18:1 ω7c. The major respiratory quinone is Q8. The polar lipid profile consisted of diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylglycerol, and 6 unknown lipids. The mol G + C% content of the genomic DNA of strain Arafor3T was 53.49%. Hence, Arafor3T represents a novel species within the genus Serratia, for which the name Serratia silvae sp. nov. is proposed. The type strain is Arafor3T (=LMG 32338T = CIP 111939T).
Assuntos
Ácidos Graxos , Fosfolipídeos , Análise de Sequência de DNA , Filogenia , RNA Ribossômico 16S/genética , DNA Bacteriano/genética , Serratia/genética , Hibridização de Ácido Nucleico , Florestas , Técnicas de Tipagem BacterianaRESUMO
Most bacterial identification methods require extensive culturing, strain purification and DNA extraction protocols. This leads to additional expenses and time lags when isolating specific bacteria from complex microbiological ecosystems. This study aimed to develop a fast and robust method for identification of lactobacilli, bifidobacteria and Bacteroides in human faecal samples. Bacteria from faecal samples were cultured anaerobically on selective media. Sonication-based DNA extraction was performed, followed by almost complete 16S rRNA gene polymerase chain reaction amplification and MinION sequencing with the Flongle adapter. Sequence analysis was performed using NanoCLUST, while RStudio was used for graphics. For 110 of the 125 colonies investigated, 100% of reads were attributed to a single species, while the remaining 15 colonies consisted of mixtures of up to three different species. The proposed bacterial identification method is advantageous for isolating particular bacteria for which there are no exclusively selective media, as it avoids lengthy colony purification and DNA purification methods, and yields a quick colony identification with high accuracy. Therefore, this method can be used for directly screening for pure cultures of target microorganisms and is suitable for the identification of bacteria in culturomics studies.
Assuntos
Nanoporos , Humanos , RNA Ribossômico 16S/genética , Ecossistema , Bactérias/genética , Sequenciamento de Nucleotídeos em Larga Escala/métodos , DNA Bacteriano/genética , Análise de Sequência de DNA/métodosRESUMO
Here we present the description of a novel Pseudomonas species, designated Pseudomonas rustica sp. nov., which was isolated from raw milk samples obtained from Germany. Results of initial 16S rRNA gene sequence analysis assigned the strain into the genus Pseudomonas and showed Pseudomonas helmanticensis, Pseudomonas neuropathica and Pseudomonas atagonensis to be its closest relatives. Further studies including sequence analysis of the rpoB gene, multi-gene phylogenetic tree reconstruction, whole-genome sequence comparisons, cellular fatty acid analysis and chemotaxonomic characterization showed a clear separation from the known Pseudomonas species. Isolate MBT-4T was closely related to Pseudomonas helmanticensis, 'Pseudomonas crudilactis' and Pseudomonas neuropathica with average nucleotide identities based on blast values of 88.8, 88.8 and 88.6%, respectively. Therefore, the strain can be classified into the Pseudomonas koreensis subgroup of the Pseudomonas fluorescens group. The G+C content of strain MBT-4T was 58.9 mol%. The strain was catalase- and oxidase-positive, while the ß-galactosidase reaction was negative. Growth occurred between 4 and 30 °C and at pH values from pH 6.0 to 8.0. In conclusion, strain MBT-4T belongs to a novel species, for which the name Pseudomonas rustica sp. nov. is proposed. The type strain is MBT-4T (=DSM 112348T=LMG 32241T) and strain MBT-17 is also a representative of this species.
Assuntos
Ácidos Graxos , Leite , Animais , Técnicas de Tipagem Bacteriana , Composição de Bases , DNA Bacteriano/genética , Fazendas , Ácidos Graxos/química , Genes Bacterianos , Hibridização de Ácido Nucleico , Filogenia , Pseudomonas , RNA Ribossômico 16S/genética , Análise de Sequência de DNARESUMO
The complete genome sequence of the virulent bacteriophage PMBT3, isolated on the proteolytic Pseudomonas grimontii strain MBTL2-21, showed no significant similarity to other known phage genome sequences, making this phage the first reported to infect a strain of P. grimontii. Electron microscopy revealed PMBT3 to be a member of the family Siphoviridae, with notably long and flexible whiskers. The linear, double-stranded genome of 87,196 bp has a mol% G+C content of 60.4 and contains 116 predicted protein-encoding genes. A putative tellurite resistance (terB) gene, originally reported to occur in the genome of a bacterium, was detected in the genome of phage PMBT3.
Assuntos
Pseudomonas/virologia , Animais , Bacteriólise , Composição de Bases , Sequência de Bases , DNA Viral/genética , Genoma Viral/genética , Especificidade de Hospedeiro , Leite/microbiologia , Filogenia , Fagos de Pseudomonas/classificação , Fagos de Pseudomonas/genética , Fagos de Pseudomonas/fisiologia , Fagos de Pseudomonas/ultraestrutura , Siphoviridae/classificação , Siphoviridae/genética , Siphoviridae/fisiologia , Siphoviridae/ultraestrutura , Proteínas Virais/genética , Vírion/ultraestruturaRESUMO
Streptococcus thermophilus is a lactic acid bacterium commonly used for the manufacture of yogurt and specialty cheeses. Virulent phages represent a major risk for milk fermentation processes worldwide, as they can inactivate the added starter bacterial cells, leading to low-quality fermented dairy products. To date, four genetically distinct groups of phages infecting S. thermophilus have been described. Here, we describe a fifth group. Phages P738 and D4446 are virulent siphophages that infect a few industrial strains of S. thermophilus The genomes of phages P738 and D4446 were sequenced and found to contain 34,037 and 33,656 bp as well as 48 and 46 open reading frames, respectively. Comparative genomic analyses revealed that the two phages are closely related to each other but display very limited similarities to other S. thermophilus phages. In fact, these two novel S. thermophilus phages share similarities with streptococcal phages of nondairy origin, suggesting that they emerged recently in the dairy environment.IMPORTANCE Despite decades of research and adapted antiphage strategies such as CRISPR-Cas systems, virulent phages are still a persistent risk for the milk fermentation industry worldwide, as they can cause manufacturing failures and alter product quality. Phages P738 and D4446 are novel virulent phages that infect the food-grade Gram-positive bacterial species Streptococcus thermophilus These two related viruses represent a fifth group of S. thermophilus phages, as they are significantly distinct from other known S. thermophilus phages. Both phages share similarities with phages infecting nondairy streptococci, suggesting their recent emergence and probable coexistence in dairy environments. These findings highlight the necessity of phage surveillance programs as the phage population evolves in response to the application of antiphage strategies.
Assuntos
Siphoviridae/classificação , Fagos de Streptococcus/classificação , Streptococcus thermophilus/virologia , Microscopia Eletrônica de Transmissão , Análise de Sequência de DNA , Siphoviridae/genética , Siphoviridae/ultraestrutura , Fagos de Streptococcus/genética , Fagos de Streptococcus/ultraestruturaRESUMO
Yeasts are eukaryotic microorganisms which have a long history in the biotechnology of food production, as they have been used since centuries in bread-making or in the production of alcoholic beverages such as wines or beers. Relative to this importance, a lot of research has been devoted to the study of yeasts involved in making these important products. The role of yeasts in other fermentations in association with other microorganisms - mainly lactic acid bacteria - has been relatively less studied, and often it is not clear if yeasts occurring in such fermentations are contaminants with no role in the fermentation, spoilage microorganisms or whether they actually serve a technological or functional purpose. Some knowledge is available for yeasts used as starter cultures in fermented raw sausages or in the production of acid curd cheeses. This review aimed to summarize the current knowledge on the taxonomy, the presence and potential functional or technological roles of yeasts in traditional fermented plant, dairy, fish and meat fermentations.
Assuntos
Microbiologia de Alimentos , Leveduras , Animais , Cerveja , Pão , FermentaçãoRESUMO
The genus Lactobacillus comprises 261 species (at March 2020) that are extremely diverse at phenotypic, ecological and genotypic levels. This study evaluated the taxonomy of Lactobacillaceae and Leuconostocaceae on the basis of whole genome sequences. Parameters that were evaluated included core genome phylogeny, (conserved) pairwise average amino acid identity, clade-specific signature genes, physiological criteria and the ecology of the organisms. Based on this polyphasic approach, we propose reclassification of the genus Lactobacillus into 25 genera including the emended genus Lactobacillus, which includes host-adapted organisms that have been referred to as the Lactobacillus delbrueckii group, Paralactobacillus and 23 novel genera for which the names Holzapfelia, Amylolactobacillus, Bombilactobacillus, Companilactobacillus, Lapidilactobacillus, Agrilactobacillus, Schleiferilactobacillus, Loigolactobacilus, Lacticaseibacillus, Latilactobacillus, Dellaglioa, Liquorilactobacillus, Ligilactobacillus, Lactiplantibacillus, Furfurilactobacillus, Paucilactobacillus, Limosilactobacillus, Fructilactobacillus, Acetilactobacillus, Apilactobacillus, Levilactobacillus, Secundilactobacillus and Lentilactobacillus are proposed. We also propose to emend the description of the family Lactobacillaceae to include all genera that were previously included in families Lactobacillaceae and Leuconostocaceae. The generic term 'lactobacilli' will remain useful to designate all organisms that were classified as Lactobacillaceae until 2020. This reclassification reflects the phylogenetic position of the micro-organisms, and groups lactobacilli into robust clades with shared ecological and metabolic properties, as exemplified for the emended genus Lactobacillus encompassing species adapted to vertebrates (such as Lactobacillus delbrueckii, Lactobacillus iners, Lactobacillus crispatus, Lactobacillus jensensii, Lactobacillus johnsonii and Lactobacillus acidophilus) or invertebrates (such as Lactobacillus apis and Lactobacillus bombicola).
Assuntos
Lactobacillaceae/classificação , Lactobacillus/classificação , Leuconostocaceae/classificação , Filogenia , Técnicas de Tipagem Bacteriana , DNA Bacteriano/genética , Análise de Sequência de DNARESUMO
The Siphoviridae phage PMBT6 was identified by transmission electron microscopy in the supernatant of Bifidobacterium thermophilum MBT94004 bioreactor fermentation culture, where it occurred at a moderately high titer. Genome analysis of the bacterial DNA confirmed the presence of this prophage within the genome of the lysogenic host. Under laboratory conditions, the prophage could not be induced by mitomycin C, ultraviolet C irradiation or hydrogen peroxide, suggesting that the prophage was released by spontaneous induction under (yet unknown) bioreactor conditions. Genome sequencing of the virion resulted in a linear, double-stranded DNA molecule of 36,561 bp with a mol% G + C content of 61.7 and 61 predicted open reading frames with low similarity to other Bifidobacterium spp. genomes, confirming that PMBT6 represents a novel temperate phage for this genus.
Assuntos
Bacteriófagos/genética , Bifidobacterium/crescimento & desenvolvimento , Sequenciamento Completo do Genoma/métodos , Bacteriófagos/classificação , Bacteriófagos/ultraestrutura , Composição de Bases , Bifidobacterium/virologia , Reatores Biológicos/microbiologia , Fermentação , Tamanho do Genoma , Genoma Viral , Microscopia Eletrônica de Transmissão , Fases de Leitura Aberta , Prófagos/classificação , Prófagos/genéticaRESUMO
In this study, 53 Staphylococcus (S.) aureus strains were typed by 16S-23S rDNA intergenic spacer region (ISR) typing and staphylococcal enterotoxin gene (SEg) typing for all the staphylococcal enterotoxin (se) and staphylococcal enterotoxin-like toxin (sel) genes known to date, revealing a higher discriminatory power than that of multi locus sequence typing. Six strains, one of each ISR- and SEg-type, were genome sequenced and the ability to produce some classical and new SEs when growing in milk was investigated. The manual analysis of the six genomes allowed us to confirm, correct and expand the results of common available genomic data pipelines such as VirulenceFinder. Moreover, it enabled us to (i) investigate the actual location of se and sel genes, even for genes such as selY, whose location (in the core genome) was so far unknown, (ii) find novel allelic variants of se and sel genes and pseudogenes, (iii) correctly annotate se and sel genes and pseudogenes, and (iv) discover a novel type of enterotoxin gene cluster (egc), i.e. the egc type 5 in strains 356P and 364P, while S. argenteus MSHR1132 harbored the egc type 6. Four of the six S. aureus strains produced sufficient amounts of SEA, SEC, SED and SEH in milk to cause staphylococcal food poisoning (SFP), with S. aureus 372 P being the highest producer of SED in milk found to date, producing as much as ca. 47,300 ng/mL and 49,200 ng/mL of SED, after 24 and 48 h of incubation in milk at 37 °C, respectively. S. aureus 372 P released a low amount of SER in milk, most likely because the seR gene was present as a pseudogene, putatively encoding only 51 amino acids. These findings confirm that not only the classical SEs, but also the new ones can represent a potential hazard for the consumers' health if produced in foods in sufficient amounts. Therefore, the detection of SEs in foods, especially if involved in SFP cases, should focus not only on classical, but also on all the new SEs and SEls known to date. Where reference methods are unavailable, the presence of the relevant genes, by using the conventional and real time PCR protocols we exhaustively provided herein, and their nucleotide sequences, should be investigated.
Assuntos
Enterotoxinas/genética , Genoma Bacteriano , Leite/microbiologia , Alimentos Crus/microbiologia , Staphylococcus aureus/classificação , Staphylococcus aureus/patogenicidade , Animais , Técnicas de Tipagem Bacteriana , DNA Bacteriano/genética , Microbiologia de Alimentos/métodos , Família Multigênica , Tipagem de Sequências Multilocus , Intoxicação Alimentar Estafilocócica/prevenção & controle , Staphylococcus aureus/isolamento & purificação , Sequenciamento Completo do GenomaRESUMO
Milk and milk products have been utilized by humans for many thousands of years. With the advent of metagenomic studies, our knowledge on the microbiota of milk and milk products, especially as affected by the environment, production, and storage parameters, has increased. Milk quality depends on chemical parameters (fat and protein content and absence of inhibitory substances), as well as microbial and somatic cells counts, and affects the price of milk. The effects of hygiene and effective cooling on the spoilage microbiota have shown that proteolytic and lipolytic bacteria such as Pseudomonas or Acinetobacter spp. predominate the spoilage bacterial populations. These bacteria can produce heat-stable proteases and lipases, which remain active after pasteurization and thus can spoil the milk during prolonged storage. Additionally, milk can become contaminated after pasteurization and therefore there is still a high demand on developing better cleaning and sanitation regimes and equipment, as well as test systems to (quantitatively) detect relevant pathogenic or spoilage microorganisms. Raw milk and raw milk cheese consumption is also increasing worldwide with the growing demand of minimally processed, sustainable, healthy, and local foods. In this context, emerging and re-emerging pathogens once again represent a major food safety challenge. As a result of global warming, it is conceivable that not only microbiological risks but also chemical risks relating to presence of mycotoxins or plant toxins in milk will increase. Herein, we provide an overview of the major microbial hazards occurring in the 21st century.
Assuntos
Laticínios/microbiologia , Microbiologia de Alimentos , Leite/microbiologia , Animais , Bactérias/crescimento & desenvolvimento , Laticínios/normas , Qualidade dos Alimentos , Inocuidade dos Alimentos , Leite/normasRESUMO
The evolution of asexual organisms is driven not only by the inheritance of genetic modification but also by the acquisition of foreign DNA. The contribution of vertical and horizontal processes to genome evolution depends on their rates per year and is quantified by the ratio of recombination to mutation. These rates have been estimated for bacteria; however, no estimates have been reported for phages. Here, we delineate the contribution of mutation and recombination to dsDNA phage genome evolution. We analyzed 34 isolates of the 936 group of Siphoviridae phages using a Lactococcus lactis strain from a single dairy over 29 years. We estimate a constant substitution rate of 1.9 × 10-4 substitutions per site per year due to mutation that is within the range of estimates for eukaryotic RNA and DNA viruses. The reconstruction of recombination events reveals a constant rate of five recombination events per year and 4.5 × 10-3 nucleotide alterations due to recombination per site per year. Thus, the recombination rate exceeds the substitution rate, resulting in a relative effect of recombination to mutation (r/m) of â¼24 that is homogenous over time. Especially in the early transcriptional region, we detect frequent gene loss and regain due to recombination with phages of the 936 group, demonstrating the role of the 936 group pangenome as a reservoir of genetic variation. The observed substitution rate homogeneity conforms to the neutral theory of evolution; hence, the neutral theory can be applied to phage genome evolution and also to genetic variation brought about by recombination.
Assuntos
Evolução Molecular , Genoma Viral , Siphoviridae/genética , Lactococcus lactis/virologia , Taxa de Mutação , Recombinação GenéticaRESUMO
BACKGROUND: This study aimed to evaluate the safety of raw vegetable products present on the German market regarding toxin-producing Bacillus cereus sensu lato (s.l.) group bacteria. RESULTS: A total of 147 B. cereus s.l. group strains isolated from cucumbers, carrots, herbs, salad leaves and ready-to-eat mixed salad leaves were analyzed. Their toxinogenic potential was assessed by multiplex PCR targeting the hemolysin BL (hbl) component D (hblD), non-hemolytic enterotoxin (nhe) component A (nheA), cytotoxin K-2 (cytK-2) and the cereulide (ces) toxin genes. In addition, a serological test was used to detect Hbl and Nhe toxins. On the basis of PCR and serological results, none of the strains were positive for the cereulide protein/genes, while 91.2, 83.0 and 37.4% were positive for the Hbl, Nhe and CytK toxins or their genes, respectively. Numerous strains produced multiple toxins. Generally, strains showed resistance against the ß-lactam antibiotics such as penicillin G and cefotaxim (100%), as well as amoxicillin/clavulanic acid combination and ampicillin (99.3%). Most strains were susceptible to ciprofloxacin (99.3%), chloramphenicol (98.6%), amikacin (98.0%), imipenem (93.9%), erythromycin (91.8%), gentamicin (88.4%), tetracycline (76.2%) and trimethoprim/sulfamethoxazole combination (52.4%). The genomes of eight selected strains were sequenced. The toxin gene profiles detected by PCR and serological test mostly agreed with those from whole-genome sequence data. CONCLUSIONS: Our study showed that B. cereus s.l. strains encoding toxin genes occur in products sold on the German market and that these may pose a health risk to the consumer if present at elevated levels. Furthermore, a small percentage of these strains harbor antibiotic resistance genes. The presence of these bacteria in fresh produce should, therefore, be monitored to guarantee their safety.
Assuntos
Antibacterianos/farmacologia , Bacillus cereus/fisiologia , Toxinas Bacterianas/genética , Resistência Microbiana a Medicamentos , Verduras/microbiologia , Bacillus cereus/efeitos dos fármacos , Bacillus cereus/isolamento & purificação , Contaminação de Alimentos/análise , Microbiologia de Alimentos , Regulação Bacteriana da Expressão Gênica , Genoma Bacteriano , Alemanha , Filogenia , Sequenciamento Completo do GenomaRESUMO
The meeting of International Committee on Systematics of Prokaryotes, Subcommittee on the taxonomy of Bifidobacterium,Lactobacillus and related organisms was held within the frame of the FoodMicro 2018 Congress (FoodMicro 2018, 3-6 September 2018, Berlin, Germany). The meeting comprised an open session with a workshop entitled 'Modern approaches of LAB identification and conservation' and a closed session on issues related to ICSP Subcommittee activities.
Assuntos
Terminologia como Assunto , Berlim , Bifidobacterium/classificação , Congressos como Assunto , Lactobacillus/classificaçãoRESUMO
The meeting of International Committee on Systematics of Prokaryotes, Subcommittee on the taxonomy of Bifidobacterium, Lactobacillus and related organisms was held within the frame of the FoodMicro 2016 Congress in Dublin (FoodMicro 2016, 19-22 July 2016, Dublin, Ireland). The meeting comprised an open session with a workshop entitled 'Research and networking taxonomy in food with an emphasis on LAB' and a closed session on issues related to ICSP Subcommittee activities.
RESUMO
The taxonomy of the genus Lactobacillus was revised in April 2020 to reclassify species that were originally described as Lactobacillus species into 25 genera that comprise phylogenetically related micro-organisms. The species in these 25 genera also share major metabolic traits and generally have a shared ecology. A total of four comb. nov. names, however, were not considered validly published because the valid publication of the corresponding basonyms was published in later issues of the International Journal of Systematic and Evolutionary Microbiology. This communication aims to validly publish the names Apilactobacillus bombintestini, Companilactobacillus suantsaicola, Lactiplantibacillus garii and Levilactobacillus suantsaiihabitans.
RESUMO
In this study, nine Gram-negative, motile and rod-shaped bacteria were isolated during a Germany-wide investigation of raw milk microbiota. The strains could be differentiated from their closest relatives by phenotypic and chemotaxonomic characterization and average nucleotide identity (ANIb) values calculated from draft genome assemblies. Strains MBT-1T, MBT-8, MBT-9, MBT-10, MBT-11 and MBT-12 were related to the Pseudomonas chlororaphis subgroup. Isolates MBT-2T, MBT-13 and MBT-14 were closely related to Pseudomonas rhizosphaerae DSM 16299T with an ANIb of 88.2â% and a genome-to-genome distance result of 36.0â%. The G+C content of the DNA of strains MBT-1T and MBT-2T was 60.84 and 62.48âmol%, respectively. The major fatty acids were C16â:â1 ω7c (summed feature 3), C16â:â0 and C18â:â1 ω7c (summed feature 8). The strains were catalase-positive, while production of urease, ß-galactosidase and indole were negative. Growth occurred at 4-30 °C and at pH values of pH 6.0-8.0. Based on these results, we conclude that the strains belong to two novel species, for which the names Pseudomonas kielensis sp. nov. and Pseudomonas baltica sp. nov. are proposed. The type strains are MBT-1T (=DSM 111668 T= LMG 31954T) and MBT-2T (=DSM 111761 T=LMG 31955T).
RESUMO
Phages of Streptococcus thermophilus present a major threat to the production of many fermented dairy products. To date, only a few studies have assessed the biodiversity of S. thermophilus phages in dairy fermentations. In order to develop strategies to limit phage predation in this important industrial environment, it is imperative that such studies are undertaken and that phage-host interactions of this species are better defined. The present study investigated the biodiversity and evolution of phages within an Irish dairy fermentation facility over an 11-year period. This resulted in the isolation of 17 genetically distinct phages, all of which belong to the so-called cos group. The evolution of phages within the factory appears to be influenced by phages from other dairy plants introduced into the factory for whey protein powder production. Modular exchange, primarily within the regions encoding lysogeny and replication functions, was the major observation among the phages isolated between 2006 and 2016. Furthermore, the genotype of the first isolate in 2006 was observed continuously across the following decade, highlighting the ability of these phages to prevail in the factory setting for extended periods of time. The proteins responsible for host recognition were analyzed, and carbohydrate-binding domains (CBDs) were identified in the distal tail (Dit), the baseplate proteins, and the Tail-associated lysin (Tal) variable regions (VR1 and VR2) of many isolates. This supports the notion that S. thermophilus phages recognize a carbohydrate receptor on the cell surface of their host.IMPORTANCE Dairy fermentations are consistently threatened by the presence of bacterial viruses (bacteriophages or phages), which may lead to a reduction in acidification rates or even complete loss of the fermentate. These phages may persist in factories for long periods of time. The objective of the current study was to monitor the progression of phages infecting the dairy bacterium Streptococcus thermophilus over a period of 11 years in an Irish dairy plant so as to understand how these phages evolve. A focused analysis of the genomic region that encodes host recognition functions highlighted that the associated proteins harbor a variety of carbohydrate-binding domains, which corroborates the notion that phages of S. thermophilus recognize carbohydrate receptors at the initial stages of the phage cycle.
Assuntos
Produtos Fermentados do Leite/microbiologia , Fagos de Streptococcus/genética , Streptococcus thermophilus/virologia , Evolução Biológica , Indústria de Laticínios , Fermentação , Genótipo , Especificidade de Hospedeiro , Irlanda , Lisogenia , Filogenia , Fagos de Streptococcus/classificação , Fagos de Streptococcus/isolamento & purificação , Fagos de Streptococcus/fisiologia , Streptococcus thermophilus/genética , Streptococcus thermophilus/metabolismo , Proteínas Virais/genética , Proteínas Virais/metabolismoRESUMO
A Gram-stain-negative, rod-shaped Proteobacteria isolate, MBT G8648T, was obtained from an acid curd cheese called Quargel. The isolate was moderately salt tolerant and motile, with numerous peritrichous flagella. The 16S rRNA gene sequence analysis indicated that the strain belongs to the genus Halomonas, with 98.42â% 16S rRNA gene sequence similarity with Halomonas titanicae BH1T as nearest related neighbour. Further comparative sequence analysis of secA and gyrB genes, as well as physiological and biochemical tests, revealed that this bacterium formed a taxon well-separated from its nearest neighbours and other established Halomonas species. Thus, the strain represents a new species, for which the name Halomonas nigrificans sp. nov. is proposed, with strain MBT G8648T (=LMG 29097T =DSM 105749T) as type strain.