Bacillus cytotoxicus sp. nov. is a novel thermotolerant species of the Bacillus cereus Group occasionally associated with food poisoning

Lantibiotics are ribosomally synthesized peptides that contain multiple posttranslational modifications. Research on lantibiotics has increased recently, mainly due to their broad-spectrum antimicrobial activity, especially against some clinical Gram-positive pathogens. Many reports about various bacteriocins in the Bacillus cereus group have been published, but few were about lantibiotics. In this study, we identified 101 putative lanthipeptide gene clusters from 77 out of 223 strains of this group, and these gene clusters were further classified into 20 types according to their gene organization and the homologies of their functional genes. Among them, 18 types were novel and have not yet been experimentally verified. Two novel lantibiotics (thuricin 4A-4 and its derivative, thuricin 4A-4D) were identified in the type I-1 lanthipeptide gene cluster and showed activity against all tested Gram-positive bacteria. The mode of action of thuricin 4A-4 was studied, and we found that it acted as a bactericidal compound. The transcriptional analysis of four structural genes (thiA1, thiA2, thiA3, and thiA4) in the thuricin 4A gene cluster showed that only one structural gene, thiA4, showed efficient transcription in the exponential growth phase; the other three structural genes did not. In addition, the putative transmembrane protein ThiI was responsible for thuricin 4A-4 immunity. Genome analysis and functional verification illustrated that B. cereus group strains were a prolific source of novel lantibiotics. Bacteriocins are ribosomally synthesized peptides produced by bacteria and exhibit antimicrobial activity against other bacteria (either in the same species or across genera) (1); they include posttranslationally modified bacteriocins and unmodified bacteriocins (2). Lanthipeptides (lantibiotics) are peptides that undergo multiple posttranslational modifications, and these are the best-characterized modified bacteriocins (3). Modifications include the formation of meso-lanthionine and 3-methyllanthionine as well as dehydrated amino acids (Dha and Dhb). Lanthipeptides are classified into four different classes on the basis of their biosynthetic enzymes (4). In class I lanthipeptides, the dehydration is carried out by a dehydratase (LanB) and cyclization is catalyzed by a cyclase (LanC). Class II lanthipeptides are modified by LanM proteins, which perform both dehydration and cyclization. In class III and IV lanthipeptides, the dehydration and cyclization reactions are catalyzed by multifunctional enzymes (RamC/LabKC or LanL).The Bacillus cereus group currently contains eight species: B. anthracis, B. cereus, B. thuringiensis, B. cytotoxicus, B. weihenstephanensis, B. mycoides, B. pseudomycoides, and B. toyonensis (5, 6). To date, bacteriocins of the B. cereus group have been identified or characterized mainly in strains of B. cereus and B. thuringiensis. More than 20 bacteriocins have been reported in these two species (7,8). They are active against closely related bacilli, such as the foodborne pathogen B. cereus...

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“…(5,6). To date, bacteriocins of the B. cereus group have been identified or characterized mainly in strains of B. cereus and B. thuringiensis.…”

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The Bacillus cereus Group Is an Excellent Reservoir of Novel Lanthipeptides

Xin

Zheng

et al. 2015

Appl Environ Microbiol

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“…This group comprises seven closely related species, including B. cereus sensu stricto and B. cytotoxicus, that cause emetic and/or diarrheal syndromes in food poisoning (1)(2)(3). Some rare strains of B. weihenstephanensis, another species of this bacterial group, can also be emetic (4).…”

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“…These bacteria cause a number of food safety issues, as they are able to produce heat-resistant spores and thus survive in food even after processes such as cooking or pasteurization. Compared to the incidence of food poisoning caused by B. cereus sensu stricto, food poisoning caused by B. cytotoxicus or B. weihenstephanensis is rare (1,3). The risk for consumers is mostly tied to high doses (10 5 to 10 8 CFU) of cells or spores contaminating the ingested food and thus depends on the ability of the bacterium to multiply during the food's shelf life (2,5,6).…”

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The CasKR Two-Component System Is Required for the Growth of Mesophilic and Psychrotolerant Bacillus cereus Strains at Low Temperatures

Diomandé

Chamot

Antolinos

et al. 2014

Appl Environ Microbiol

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eThe different strains of Bacillus cereus can grow at temperatures covering a very diverse range. Some B. cereus strains can grow in chilled food and consequently cause food poisoning. We have identified a new sensor/regulator mechanism involved in lowtemperature B. cereus growth. Construction of a mutant of this two-component system enabled us to show that this system, called CasKR, is required for growth at the minimal temperature (T min ). CasKR was also involved in optimal cold growth above T min and in cell survival below T min . Microscopic observation showed that CasKR plays a key role in cell shape during cold growth. Introducing the casKR genes in a ⌬casKR mutant restored its ability to grow at T min . Although it was first identified in the ATCC 14579 model strain, this mechanism has been conserved in most strains of the B. cereus group. We show that the role of CasKR in cold growth is similar in other B. cereus sensu lato strains with different growth temperature ranges, including psychrotolerant strains.

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“…To begin with, the size and GϩC content of the B. subtilis B7-S genome are 5. (37)(38)(39)(40). Although these novel Bacillus species have been proposed to belong to the Bcg, valid species descriptions still are missing.…”

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Chromosome-Directed PCR-Based Detection and Quantification of Bacillus cereus Group Members with Focus on B. thuringiensis Serovar israelensis Active against Nematoceran Larvae

Schneider

Hendriksen

Melin

et al. 2015

Appl Environ Microbiol

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e Bacillus thuringiensis serovar israelensis is a wide-spread soil bacterium affiliated with the B. cereus group (Bcg) and is widely used in biocontrol products applied against mosquito and black fly larvae. For monitoring and quantification of applied B. thuringiensis serovar israelensis and its effect on indigenous B. thuringiensis serovar israelensis and Bcg assemblages, efficient and reliable tools are essential. The abundance and properties of B. thuringiensis serovar israelensis strains in the environment traditionally have been investigated with cultivation-dependent techniques, which are hampered by low sensitivity and the morphological similarity between B. cereus and B. thuringiensis. Currently available PCR-based detection and quantification tools target markers located on plasmids. In this study, a new cultivation-independent PCR-based method for efficient and specific quantification of B. thuringiensis serovar israelensis and Bcg is presented, utilizing two sets of PCR primers targeting the bacterial chromosome. Sequence database searches and empirical tests performed on target and nontarget species, as well as on bulk soil DNA samples, demonstrated that this diagnostic tool is specific for B. thuringiensis serovar israelensis and Bcg. The method will be useful for comparisons of Bcg and B. thuringiensis serovar israelensis abundances in the same samples. Moreover, the effect of B. thuringiensis serovar israelensis-based insecticide application on the total Bcg assemblages, including indigenous populations, can be investigated. This type of information is valuable in risk assessment and policy making for use of B. thuringiensis serovar israelensis in the environment. The bacterium Bacillus thuringiensis (Bt) is one of the grand successes in microbial pest control (1). After its first discovery in 1901 and description by Berliner in 1911, the first biocontrol product based on Bt, Sporein, for control of the European corn borer (Ostrinia nubilalis), was commercially available already in 1938 (1). The crystalline, proteinaceous ␦-endotoxins of Bt are formed during sporulation, and their lethal effect is manifested only after larval ingestion of spores or free crystals (2, 3). Bt is a member of the Bacillus cereus group (Bcg), which consists of the Gram-positive rod-shaped spore-forming bacterial species B. cereus, Bt, B. anthracis, B. mycoides, B. pseudomycoides, and B. weihenstephanensis (4,5). However, a multidatatype phylogenetic analysis of Bcg strains isolated from various sample types, including environmental, clinical, food, and diary sources, did not reflect current Bcg taxonomy well. This finding indicated that the phylogeny of this bacterial group is more complicated than reflected by the division into the current six species (6).The bacterium B. thuringiensis serovar israelensis produces toxins active against nematoceran larvae and has been widely used for biocontrol of mosquitoes and black flies (3). B. thuringiensis serovar israelensis was described in 1976 (7) and has been shown to have ...

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Bacillus cytotoxicus sp. nov. is a novel thermotolerant species of the Bacillus cereus Group occasionally associated with food poisoning

Cited by 285 publications

References 41 publications

The Bacillus cereus Group Is an Excellent Reservoir of Novel Lanthipeptides

The Bacillus cereus Group Is an Excellent Reservoir of Novel Lanthipeptides

The CasKR Two-Component System Is Required for the Growth of Mesophilic and Psychrotolerant Bacillus cereus Strains at Low Temperatures

Chromosome-Directed PCR-Based Detection and Quantification of Bacillus cereus Group Members with Focus on B. thuringiensis Serovar israelensis Active against Nematoceran Larvae

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