Occurrence of Bacillus thuringiensis in fresh waters of Japan

Development of a Safe and Effective Bacillus thuringiensis-Based Nanobiopesticide for Controlling Tea Pests

Mg(OH)2 was used as the nanocarrier of the Bacillus thuringiensis (Bt) Cry1Ac protein, and the synthesized Cry1Ac-Mg(OH)2 composites were regular and uniform nanosheets. Nano-Mg(OH)2 could effectively improve the insecticidal effect of the Cry1Ac protein toward Ectropis obliqua. It could enhance the damage degree of the Cry1Ac protein to intestinal epithelial cells and microvilli, induce and enrich the production of reactive oxygen species (ROS) in the midgut, and enhance the degradation of the Cry1Ac protein into active fragments. Furthermore, an anti-rinsing assay showed that the Cry1Ac-Mg(OH)2 composites were bound to the notch structure of the tea leaf surface. The retention of the Cry1Ac protein increased by 11.45%, and sprayed nano-Mg(OH)2 was rapidly absorbed by different tissues of tea plants. Moreover, nano-Mg(OH)2 and composites did not significantly affect non-target organisms. These results show that nano-Mg(OH)2 can serve as a safe and effective biopesticide carrier, which provides a new approach for stable and efficient Bt preparation.

Silica removal at sewage treatment plants causes new silica deficiency

The dissolved silicate (DSi) concentration in coastal waters has decreased due to anthropogenic activities. Many studies have indicated that dam construction is a main reason for this reduction. However, recently, dam construction alone has not been sufficient to explain the DSi reduction in some coastal waters. In this study, we focused on silica removal at sewage treatment plants (STPs). DSi and particulate silica (PSi) concentrations were measured in STP influent and effluent waters from September 2020 to September 2021. Dissolution experiments on PSi were also conducted to estimate the fraction of soluble PSi in the STP influent. DSi and PSi were removed by 29.5% and 96.9%, respectively, at the STP. In addition, the soluble PSi in the STP influent accounted for 20.3% of the PSi removed. Therefore, in addition to the DSi removal in STPs, removal of soluble PSi can also cause potential DSi depletion in downstream and coastal waters. In addition to the effect of dams, the silica supply delivered to coastal waters may be further reduced in the future due to the progress of sewage treatment development in coastal areas.

Effects of Site-Directed Mutagenesis of Cysteine on the Structure of Sip Proteins

Bacillus thuringiensis, a gram-positive bacteria, has three insecticidal proteins: Vip (vegetative insecticidal protein), Cry (crystal), and Sip (secreted insecticidal protein). Of the three, Sip proteins have insecticidal activity against larvae of Coleoptera. However, the Sip1Aa protein has little solubility in the supernatant because of inclusion bodies. This makes it more difficult to study, and thus research on Sip proteins is limited, which hinders the study of their mechanistic functions and insecticidal mechanisms. This highlights the importance of further investigation of the Sip1Aa protein. Disulfide bonds play an important role in the stability and function of proteins. Here, we successfully constructed mutant proteins with high insecticidal activity. The tertiary structure of the Sip1Aa protein was analyzed with homologous modeling and bioinformatics to predict the conserved domain of the protein. Cysteine was used to replace amino acids via site-directed mutagenesis. We successfully constructed Sip149-251, Sip153-248, Sip158-243, and Sip178-314 mutant proteins with higher solubility than Sip1Aa. Sip153-248 and Sip158-243 were the most stable compared to Sip1Aa, followed by Sip149-251 and Sip178-314. The insecticidal activity of Sip153-248 (Sip158-243) was 2.76 (2.26) times higher than that of Sip1Aa. The insecticidal activity of Sip149-251 and Sip178-314 did not differ significantly from that of Sip1Aa. Basic structural properties, physicochemical properties, and the spatial structure of the mutation site of Sip1Aa and the mutant proteins were analyzed. These results provide a molecular basis for using Sip1Aa to control Coleopteran insects and contribute to the study of the Sip1Aa insecticidal mechanism.

Importance of Cry Proteins in Biotechnology: Initially a Bioinsecticide, Now a Vaccine Adjuvant

A hallmark of Bacillus thuringiensis bacteria is the formation of one or more parasporal crystal (Cry) proteins during sporulation. The toxicity of these proteins is highly specific to insect larvae, exerting lethal effects in different insect species but not in humans or other mammals. The aim of this review is to summarize previous findings on Bacillus thuringiensis, including the characteristics of the bacterium, its subsequent contribution to biotechnology as a bioinsecticide due to the presence of Cry proteins, and its potential application as an adjuvant. In several studies, Cry proteins have been administered together with specific antigens to immunize experimental animal models. The results have shown that these proteins can enhance immunogenicity by generating an adequate immune response capable of protecting the model against an experimental infectious challenge, whereas protection is decreased when the specific antigen is administered without the Cry protein. Therefore, based on previous results and the structural homology between Cry proteins, these molecules have arisen as potential adjuvants in the development of vaccines for both animals and humans. Finally, a model of the interaction of Cry proteins with different components of the immune response is proposed.

Dissecting the Environmental Consequences of Bacillus thuringiensis Application for Natural Ecosystems

Bacillus thuringiensis (Bt), a natural pathogen of different invertebrates, primarily insects, is widely used as a biological control agent. While Bt-based preparations are claimed to be safe for non-target organisms due to the immense host specificity of the bacterium, the growing evidence witnesses the distant consequences of their application for natural communities. For instance, upon introduction to soil habitats, Bt strains can affect indigenous microorganisms, such as bacteria and fungi, and further establish complex relationships with local plants, ranging from a mostly beneficial demeanor, to pathogenesis-like plant colonization. By exerting a direct effect on target insects, Bt can indirectly affect other organisms in the food chain. Furthermore, they can also exert an off-target activity on various soil and terrestrial invertebrates, and the frequent acquisition of virulence factors unrelated to major insecticidal toxins can extend the Bt host range to vertebrates, including humans. Even in the absence of direct detrimental effects, the exposure to Bt treatment may affect non-target organisms by reducing prey base and its nutritional value, resulting in delayed alleviation of their viability. The immense phenotypic plasticity of Bt strains, coupled with the complexity of ecological relationships they can engage in, indicates that further assessment of future Bt-based pesticides' safety should consider multiple levels of ecosystem organization and extend to a wide variety of their inhabitants.

Exploration of insecticidal potential of Cry protein purified from Bacillus thuringiensis VIID1

Insect pests are a threat to agriculture as they cause a loss of 15-22% to economically important crops every year. Bacillus thuringiensis produces parasporal crystal inclusions that have insecticidal 'Cry' proteins which are toxic to insect larvae of the order Lepidoptera, Coleoptera and Diptera, etc. In the present study, 40 different soil samples from Amritsar and its surrounding areas were selected for isolation of B. thuringiensis. The rod shaped, gram-positive bacterial isolates were further analyzed for characteristic crystal formation using phase contrast and scanning electron microscopy. 6 Bacillus samples containing cry genes were identified using the universal primers for cry genes, of which one isolate exhibited a protein band of ~95 kDa. This protein was purified using a Sephadex G-75 column. The insecticidal assays conducted with purified Cry protein on insect larvae of lepidopteran and dipteran orders viz. Spodoptera litura, Galleria malonella, Bactrocera cucurbitae and Culex pipens revealed considerable detrimental effects. A significant increase in larval mortality was observed for the larvae of all insects in a concentration dependent manner when treated with Cry protein purified from B. thuringenisis VIID1. The purified Cry protein did not have any significant effect on honey bee larvae.

Genome Sequence of Bacillus thuringiensis Strain MW, a Freshwater Isolate

Bacillus thuringiensis is an agriculturally significant bacterium and common biological pesticide. B. thuringiensis strain MW was isolated from a freshwater stream in Mont Vernon, NH, and sequenced. A draft genome assembly of 5,935,630 bp with a G+C content of 34.86% and an N 50 value of 1,154,949 bp was generated.

Spores and vegetative cells of phenotypically and genetically diverse Bacillus cereus sensu lato are common bacteria in fresh water of northeastern Poland

Gram-positive rods Bacillus cereus sensu lato (sl) are common in natural habitats and food products. It is believed that they are restricted to spores; however, their ecology in aquatic habitats is still poorly investigated. Thus, the aim of the study was to assess the rain-dependent fluctuations in the concentration of B. cereus sl vegetative cells and spores, with evaluation of their phylogenetic and population structure in relation to the toxicity and psychrotolerance. We proved that vegetative cells of B. cereus sl are widely distributed in fresh water of rivers and lakes, being as common as spores. Moreover, heavy rain has a huge impact on their concentration in undisturbed environments. The diversity of B. cereus sl reflects the multiple sources of bacteria and the differences between their distinct environments. Next, their diverse genetic structure and phenotypes better fit their ecological properties than their taxonomic affiliation.

Molecular characterization of indigenous Bacillus thuringiensis strains isolated from Kashmir valley

Bacillus thuringiensis (Bt) being an eco-friendly bioinsecticide is effectively used in pest management strategies and, therefore, isolation and identification of new strains effective against a broad range of target pests is important. In the present study, new indigenous B. thuringiensis strains were isolated and investigated so that these could be used as an alternative and/or support the current commercial strains/cry proteins in use. For this, 159 samples including soil, leaf and spider webs were collected from ten districts of Kashmir valley (India). Of 1447 bacterial strains screened, 68 Bt strains were identified with 4 types of crystalline inclusions. Crystal morphology ranking among the Bt strains was spherical (69.11%) > spore attached (8.82%) > rod (5.88%) = bipyramidal (5.88%) > spherical plus rod (4.41%) > spherical plus bipyramidal (2.94%) = cuboidal (2.94%). SDS-PAGE investigation of the spore-crystal mixture demonstrated Bt strains contained proteins of various molecular weights ranging from 150 to 28 kDa. Insecticidal activity of the 68 indigenous Bt strains against Spodoptera litura neonates showed that Bt strain SWK1 strain had the highest mortality. Lepidopteron active genes (cry1, cry2Ab, cry2Ab) were present in six Bt strains. Further, analysis of a full-length cry2A gene (~1.9 kb) by PCR-RFLP in strain SWK1 revealed that it was a new cry2A gene in Bt strain SWK1 and was named as cry2Al1 (GenBank Accession No. KJ149819.1) using the Bt toxin nomenclature ( http://www.btnomenclature.info ). Insect bioassays with neonate larvae of S. litura and H. armigera showed that the purified Cry2Al1 is toxic to S. litura with LC₅₀ 2.448 µg/ml and H. armigera with LC₅₀ 3.374 µg/ml, respectively. However, it did not produce any mortality in third instar larvae of Aedes aegypti, Culex quinquefasciatus and Anopheles stephensi larvae/pupae insects (100 µg/ml) at 28 ± 2 °C and 75 to 85% relative humidity under a photoperiod of 14L:10D.

Pen and Pal are nucleotide-sugar dehydratases that convert UDP-GlcNAc to UDP-6-deoxy-D-GlcNAc-5,6-ene and then to UDP-4-keto-6-deoxy-L-AltNAc for CMP-pseudaminic acid synthesis in Bacillus thuringiensis

CMP-pseudaminic acid is a precursor required for the O-glycosylation of flagellin in some pathogenic Gram-negative bacteria, a process known to be critical in bacterial motility and infection. However, little is known about flagellin glycosylation in Gram-positive bacteria. Here, we identified and functionally characterized an operon, named Bti_pse, in Bacillus thuringiensis israelensis ATCC 35646, which encodes seven different enzymes that together convert UDP-GlcNAc to CMP-pseudaminic acid. In contrast, Gram-negative bacteria complete this reaction with six enzymes. The first enzyme, which we named Pen, converts UDP-d-GlcNAc to an uncommon UDP-sugar, UDP-6-deoxy-D-GlcNAc-5,6-ene. Pen contains strongly bound NADP(+) and has distinct UDP-GlcNAc 4-oxidase, 5,6-dehydratase, and 4-reductase activities. The second enzyme, which we named Pal, converts UDP-6-deoxy-D-GlcNAc-5,6-ene to UDP-4-keto-6-deoxy-L-AltNAc. Pal is NAD(+)-dependent and has distinct UDP-6-deoxy-d-GlcNAc-5,6-ene 4-oxidase, 5,6-reductase, and 5-epimerase activities. We also show here using NMR spectroscopy and mass spectrometry that in B. thuringiensis, the enzymatic product of Pen and Pal, UDP-4-keto-6-deoxy-L-AltNAc, is converted to CMP-pseudaminic acid by the sequential activities of a C4″-transaminase (Pam), a 4-N-acetyltransferase (Pdi), a UDP-hydrolase (Phy), an enzyme (Ppa) that adds phosphoenolpyruvate to form pseudaminic acid, and finally a cytidylyltransferase that condenses CTP to generate CMP-pseudaminic acid. Knowledge of the distinct dehydratase-like enzymes Pen and Pal and their role in CMP-pseudaminic acid biosynthesis in Gram-positive bacteria provides a foundation to investigate the role of pseudaminic acid and flagellin glycosylation in Bacillus and their involvement in bacterial motility and pathogenicity.

Occurrence of Bacillus thuringiensis and their phages in Yemen soil

Bacillus thuringiensis (Bt) isolates were found in all samples of soil in nine Governorates of Yemen. From 384 isolates of Bacillus recovered from these soil samples after acetate selection, 104 isolates (27.1 %) were Bt. Five isolates of Bt were selected and insecticidal activity was tested against Culex pipiens, Callosobruchus maculatus and Spodoptera littoralis. The Bt isolate YH18 gave toxicity to all tested insects larvae. This study extended to isolate phages active against the selected Bt isolates. Five phages were isolated and classified into two groups of tailed phages. Four phages with long non-contractile tails and hexagonal heads (Siphoviridae) and one phage with very short tail and isometric head (Podoviridae). Susceptibility of selected Bt to infect by these phages was studied by spot-test technique. Also the Bt isolate no YH18 was resistant to all tested phages. This is the first report illustrates the diversity and the abundance of Bt and Bt phage in Yemen soil.

Bacillus thuringiensis Is an Environmental Pathogen and Host-Specificity Has Developed as an Adaptation to Human-Generated Ecological Niches

Bacillus thuringiensis (Bt) has been used successfully as a biopesticide for more than 60 years. More recently, genes encoding their toxins have been used to transform plants and other organisms. Despite the large amount of research on this bacterium, its true ecology is still a matter of debate, with two major viewpoints dominating: while some understand Bt as an insect pathogen, others see it as a saprophytic bacteria from soil. In this context, Bt's pathogenicity to other taxa and the possibility that insects may not be the primary targets of Bt are also ideas that further complicate this scenario. The existence of conflicting research results, the difficulty in developing broader ecological and genetics studies, and the great genetic plasticity of this species has cluttered a definitive concept. In this review, we gathered information on the aspects of Bt ecology that are often ignored, in the attempt to clarify the lifestyle, mechanisms of transmission and target host range of this bacterial species. As a result, we propose an integrated view to account for Bt ecology. Although Bt is indeed a pathogenic bacterium that possesses a broad arsenal for virulence and defense mechanisms, as well as a wide range of target hosts, this seems to be an adaptation to specific ecological changes acting on a versatile and cosmopolitan environmental bacterium. Bt pathogenicity and host-specificity was favored evolutionarily by increased populations of certain insect species (or other host animals), whose availability for colonization were mostly caused by anthropogenic activities. These have generated the conditions for ecological imbalances that favored dominance of specific populations of insects, arachnids, nematodes, etc., in certain areas, with narrower genetic backgrounds. These conditions provided the selective pressure for development of new hosts for pathogenic interactions, and so, host specificity of certain strains.

Identification of a second cytotoxic protein produced by Bacillus thuringiensis A1470

Bacillus thuringiensis A1470 produces multiple proteins with similar molecular masses (~30 kDa) with cytotoxicity against human cell lines. One that was previously identified, parasporin-4, is a β-pore-forming toxin. The N-terminal sequence of a second cytotoxic protein was identical to a partial sequence of parasporin-2 produced by B. thuringiensis A1547. PCR was performed on total plasmid DNA from A1470 by using primers for parasporin-2 to amplify a gene which was then cloned. The cloned gene differed from A1547 parasporin-2 by 8 bp and the predicted protein differed by four amino acids. The gene was expressed in Escherichia coli, and the cytotoxic activities of the recombinant protein against four human cell lines (MOLT-4, Jurkat, HeLa, and HepG2) were similar to those of A1547 parasporin-2. We then confirmed that the A1470 strain simultaneously produces parasporin-2 and parasporin-4.

Effect of vegetation on the presence and genetic diversity of Bacillus thuringiensis in soil

Bacillus thuringiensis isolates were obtained from soil samples collected at different sites located in the same region but with different vegetation. The sites showed different frequencies of B. thuringiensis, depending on the type of vegetation. Strains of B. thuringiensis were found to be less common in samples of riparian forest soil than in soil of other types of vegetation. The rate of occurrence of B. thuringiensis in the samples also varied according to the vegetation. These results show that whenever this bacterium was found, it showed a high rate of occurrence, indicating that this species could be better adapted to using soil as a reservoir than other Bacillus species. The presence of cry genes was analyzed by polymerase chain reaction, and genes that exhibited activity against Diptera species were the most commonly found. The isolates obtained were characterized by random amplified polymorphic DNA, and 50% were clustered into clonal groups. These results demonstrated the possible occurrence of a high number of genetically similar strains when samples are collected from the same region, even if they are from locations with different vegetation.

Microbial ecology and association of Bacillus thuringiensis in chicken feces originating from feed

To explain the association of Bacillus thuringiensis (Bt) with animal feces, an ecological analysis in chickens was conducted by introducing a cry(-) strain marked by production of green fluorescent protein (GFP). After feeding with the tagged Bt strains, the feces of the tested chickens were collected at different times, isolated, and the morphology of Bt was observed. It was shown that Bt strain HD-73GFP in spore form could be isolated from feces of chickens for a period of 13 d, and then it disappeared thereafter. Bt could be detected only up to day 4 (but not thereafter), when chickens were fed with vegetative cells of HD-73GFP. To confirm the source of newly isolated strains, the gfp gene was examined by polymerase chain reaction (PCR), which showed that all the isolated strains harbored the marker gene. Recent data from isolation and PCR had suggested that fecal Bt strains had originated from food. Chicken tissues were thus dissected to isolate Bt strains and to investigate whether Bt could be located in vivo. Bt was located within the duodenum in spore form. Compared to the morphology of the isolated strains at different growth times, the growth rates of all the tested Bt had little changes when passing through the digestive system to the feces. Dissection of the chickens confirmed that Bt was safe for the tested animal.

Screening, diversity and partial sequence comparison of vegetative insecticidal protein (vip3A) genes in the local isolates of Bacillus thuringiensis Berliner

Characterization, direct sequencing of the PCR amplicon and phylogenetic relationship was done to discover a novel Vip protein genes of the Bt isolates, to improve the prospects for insect control, more Vip proteins should be sought out and researched to predict their insecticidal activity. Characterization was based on direct sequencing of PCR amplicon using primers specific to vip3A gene was presented here. 12 out of 18 isolates screened were positive for vip gene-specific primers. Homology search for the partial sequences using BLAST showed that 11 isolates had high similarity to vip3Aa gene and only one fragment with vip3Ae gene (25-100% at nucleotide and amino acid level). Phylogenetic analysis showed that the gene sequences were responsible for geographic separation for divergence within vip genes, consistent with the evaluation of distinct bacterial population. Despite the geographical distances, strains harbouring vip genes have originated from common ancestors may significantly contribute to control resistant insect pests. Some strains have evolved to be quite distinct and others remain as members of closely related groups. The reported method is a powerful tool to find novel Vip3A proteins from large-scale Bt strains which is effective in terms of time and cost. Further the Vip proteins produced by different strains of B. thuringiensis are unique in terms of the sequence divergence and hence may also differ in their insecticidal activities.

Health considerations regarding horizontal transfer of microbial transgenes present in genetically modified crops

The potential effects of horizontal gene transfer on human health are an important item in the safety assessment of genetically modified organisms. Horizontal gene transfer from genetically modified crops to gut microflora most likely occurs with transgenes of microbial origin. The characteristics of microbial transgenes other than antibiotic-resistance genes in market-approved genetically modified crops are reviewed. These characteristics include the microbial source, natural function, function in genetically modified crops, natural prevalence, geographical distribution, similarity to other microbial genes, known horizontal transfer activity, selective conditions and environments for horizontally transferred genes, and potential contribution to pathogenicity and virulence in humans and animals. The assessment of this set of data for each of the microbial genes reviewed does not give rise to health concerns. We recommend including the above-mentioned items into the premarket safety assessment of genetically modified crops carrying transgenes other than those reviewed in the present study.

Water distribution systems as living ecosystems: impact on taste and odor

Six waters from different U.S. cities with known diverse taste and odor (TO) evaluations were selected for additional microbial characterization. All waters were subjected to microbial and cultural analyses, and four of the waters were further analyzed by cloning and sequencing of community 16S rRNA. The purpose of the study was to evaluate water distribution systems as living ecosystems, and the impact of these ecosystems on TO. All waters had total bacterial counts of at least 10(3) per ml. The water with lowest TO ranking had 10(6) total counts per ml. Community DNA sequence analysis identified diverse bacterial communities representing five different phyla and over forty genera. Included in this diversity were heterotrophic and autotrophic species that were both aerobic or anaerobic. Additionally, waters with the lowest TO evaluations contained significant sulfide concentrations, as well as bacteria associated with both the oxidation and reduction of inorganic sulfur compounds. Low redox conditions could have resulted in the reduced sulfur compounds and concomitant TO related problems, and an increase in redox could help alleviate these problems. Overall, data show that water distribution systems contain living ecosystems that evolve based on specific environments within particular distribution systems that impact water TO.

The occurrence of Bacillus cereus, B. thuringiensis and B. mycoides in Chinese pasteurized full fat milk

In 2006, a total of 54 samples of pasteurized full fat milk packaged in cartons were collected in spring and in autumn from chain supermarkets in Wuhan, China. The samples were examined and enumerated by MPN methods strictly according to guidelines laid out in US FDA/CFSAN BAM Chapter 14. Among 102 isolated B. cereus-like bacteria, 92 isolates were identified to be B. cereus, 9 B. thuringiensis and 1 B. mycoides. It was found that the occurrences of B. cereus were 71.4% and 33.3% in spring and in autumn samples respectively and the average count among the positive samples was 11.7 MPN/ml. The PCR detection results revealed that the enterotoxin genes hblA, hblC, hblD, nheA, nheB and nheC occurred in B. cereus isolates with frequencies of 37.0%, 66.3%, 71.7%, 71.7%, 62.0% and 71.7% respectively. Nine B. thuringiensis isolates were also identified from six pasteurized milk samples, and most of them harbored six enterotoxic genes and the insecticidal toxin cry1A gene. The single B. mycoides isolate harbored nheA and nheC genes. The data provides information for further evaluating the effect of B. cereus-like bacteria on food safety of Chinese milk products.

Novel isolate of Bacillus thuringiensis subsp. thuringiensis that produces a quasicuboidal crystal of Cry1Ab21 toxic to larvae of Trichoplusia ni

A new isolate (IS5056) of Bacillus thuringiensis subsp. thuringiensis that produces a novel variant of Cry1Ab, Cry1Ab21, was isolated from soil collected in northeastern Poland. Cry1Ab21 was composed of 1,155 amino acids and had a molecular mass of 130.5 kDa, and a single copy of the gene coding for this endotoxin was located on a approximately 75-kbp plasmid. When synthesized by the wild-type strain, Cry1Ab21 produced a unique, irregular, bipyramidal crystal whose long and short axes were both approximately 1 microm long, which gave it a cuboidal appearance in wet mount preparations. In diet incorporation bioassays, the 50% lethal concentrations of the crystal-spore complex were 16.9 and 29.7 microg ml(-1) for second- and fourth-instar larvae of the cabbage looper, Trichoplusia ni, respectively, but the isolate was essentially nontoxic to larvae of the beet armyworm, Spodoptera exigua. A bioassay of autoclaved spore-crystal preparations showed no evidence of beta-exotoxin activity, indicating that toxicity was due primarily to Cry1Ab21. Studies of the pathogenesis of isolate IS5056 in second-instar larvae of T. ni showed that after larval death the bacterium colonized and subsequently sporulated extensively throughout the cadaver, suggesting that other bacteria inhabiting the midgut lumen played little if any role in mortality. As T. ni is among the most destructive pests of vegetable crops in North America and has developed resistance to B. thuringiensis, this new isolate may have applied value.

Diversity of Colombian strains of Bacillus thuringiensis with insecticidal activity against dipteran and lepidopteran insects

AIM

To evaluate the genetic and molecular diversity and insecticidal activity of Bacillus thuringiensis isolates from all the natural regions of Colombia.

METHODS AND RESULTS

A total of 445 isolates from a collection of B. thuringiensis were characterized. The parasporal crystal morphology that was most abundant was bipyramidal (60%). Almost 10% of the isolates were toxic to Spodoptera frugiperda and 5.6% against Culex quinquefasciatus larvae. cry gene content determined by PCR indicated that 10.6% of the isolates contained cry1 genes and 1.1% contained cry2, cry4 or cry11 genes. Protein content of the parasporal crystal was determined by SDS-PAGE; 25 and 18 different protein profiles were found in isolates active against S. frugiperda and C. quinquefasciatus, respectively.

CONCLUSIONS

Bacillus thuringiensis presents great genetic and molecular diversity even in isolates from the same soil sample. Moreover, the diversity and activity of the isolates might have a relationship with the geographical origin of the samples.

SIGNIFICANCE AND IMPACT OF THE STUDY

The results obtained here indicate that some of the B. thuringiensis isolates characterized in this study are potential control agents that could be used in programmes against mosquitoes and S. frugiperda.

A novel Bacillus thuringiensis strain LLB6, isolated from bryophytes, and its new cry2Ac-type gene

AIMS

To isolate and characterize the novel Bacillus thuringiensis strains from bryophytes collected from Wuyi Mountain, Fujian Province of China, and identify new B. thuringiensis strains and toxins active against mosquitoes.

METHODS AND RESULTS

Twelve novel B. thuringiensis strains were isolated from 76 bryophyte samples. According to the results of this preliminary screening, LLB6 was the most toxic to Aedes albopictus. Then phase-contrast as well as scanning electron microscopy, bioassays, cloning, sequencing and expression were performed to characterize the novel isolate LLB6 and its new gene cry2Ac5.

CONCLUSIONS

Bacillus thuringiensis occurred naturally on bryophytes. LLB6 isolated from Physcomitrium japonicum was toxic to A. albopictus. A new cry2Ac5 gene of LLB6 was detected, cloned and expressed successfully. Bioassays on A. albopictus showed that the expressed Cry2Ac5 was also toxic to the third instar larvae.

SIGNIFICANCE AND IMPACT OF THE STUDY

This is the first report of B. thuringiensis strains isolated from bryophytes. It represents a specific source of new B. thuringiensis strains and is of great importance for the knowledge of the ecology of B. thuringiensis. Novel LLB6 harboring the new gene cry2Ac5 and its expressed Cry2Ac5 protein revealed activity against A. albopictus and became a new member of B. thuringiensis toxins.

Low persistence of Bacillus thuringiensis serovar israelensis spores in four mosquito biotopes of a salt marsh in southern France

We studied the persistence of Bacillus thuringiensis serovar israelensis (Bti) in a typical breeding site of the mosquito Ochlerotatus caspius in a particularly sensitive salt marsh ecosystem following two Bti-based larvicidal applications (Vectobac 12AS, 1.95 L/ha). The treated area was composed of four larval biotopes that differed in terms of the most representative plant species (Sarcocornia fruticosa, Bolboschoenus maritimus, Phragmites australis, and Juncus maritimus) and the physical and chemical characteristics of the soil. We sampled water, soil, and plants at various times before and after the applications (from spring to autumn, 2001) and quantified the spores of B. thuringiensis (Bt) and Bacillus species. The B. cereus group accounted for between 0% and 20% of all Bacillus spp. before application depending on the larval biotope. No Bti were found before application. The variation in the quantity of bacilli during the mosquito breeding season depended more on the larval biotope than on the season or the larvicidal application. More bacilli were found in soil (10(4)-10(6) spores/g) than on plant samples (10(2)-10(4) spores/g). The abundance in water (10(5) to 10(7) spores/L) appeared to be correlated to the water level of the breeding site. The number of Bti spores increased just after application, after declining; no spores were detected in soil or water 3 months after application. However, low numbers of Bti spores were present on foliage from three of the four studied plant strata. In conclusion, the larvicidal application has very little impact on Bacillus spp. flora after one breeding season (two applications).

Isolation and toxicity of Bacillus thuringiensis from potato-growing areas in Bolivia

Bacillus thuringiensis was isolated from 116 samples collected in high altitude potato-growing areas in Bolivia. In these regions, main potato pests are the potato tuberworm Phthorimaea operculella, and the Andean weevils Premnotrypes latithorax and Rhigopsidius tucumanus. B. thuringiensis was found in 60% of the samples. The main percentage of samples with B. thuringiensis was found in larvae of R. tucumanus (78%). Bioassays were performed with 112 isolates. None resulted toxic to either larvae or adults of the two Andean weevils. However, 18 isolates from this study showed more toxicity against the beet armyworm Spodoptera exigua than the standard strain var. kurstaki isolated from DELFIN. Among these isolates, three were also effective against P. operculella, conferring better or equal protection to the tubers than the reference strain HD-1 isolated from DIPEL. The most toxic strains against S. exigua and P. operculella were characterized in terms of serotyping, crystal morphology, protein profile, and cry gene content. PCR was performed with primers amplifying genes from the cry1, cry2, cry3, cry4, cry7, 8, and cry9Aa families. The toxic strains presented bipyramidal crystals, at least a band of 130kDa in SDS-PAGE, and showed an amplification product with cry1 family primers. One of the isolates did not amplify with any specific primer belonging to known cry1 genes. Restriction Fragment Length Polymorphism (RFLP) confirmed the presence of a novel gene and sequence comparison showed that this gene had homology to cry1G.

Cytotoxic Bacillus spp. belonging to the B. cereus and B. subtilis groups in Norwegian surface waters

AIMS

To investigate the presence and numbers of Bacillus spp. spores in surface waters and examine isolates belonging to the B. cereus and B. subtilis groups for cytotoxicity, and to discuss the presence of cytotoxic Bacillus spp. in surface water as hazard identification in a risk assessment approach in the food industry.

METHODS AND RESULTS

Samples from eight different rivers with variable degree of faecal pollution, and two drinking water sources, were heat shocked and examined for the presence of Bacillus spp. spores using membrane filtration followed by cultivation on bovine blood agar plates. Bacillus spp. was present in all samples. The numbers varied from 15 to 1400 CFU 100 ml(-1). Pure cultures of 86 Bacillus spp. isolates representing all sampling sites were characterized using colony morphology, atmospheric requirements, spore and sporangium morphology, and API 50 CHB and API 20E. Bacillus spp. representing the B. cereus and B. subtilis groups were isolated from all samples. Twenty-one isolates belonging to the B. cereus and B. subtilis groups, representing eight samples, were screened for cytotoxicity. Nine strains of B. cereus and five strains belonging to the B. subtilis group were cytotoxic.

CONCLUSIONS

The presence of cytotoxic Bacillus spp. in surface water represents a possible source for food contamination. Filtration and chlorination of surface water, the most common drinking water treatment in Norway, do not remove Bacillus spores efficiently. This was confirmed by isolation of spores from tap water samples.

SIGNIFICANCE AND IMPACT OF THE STUDY

Contamination of food with water containing low numbers of Bacillus spores implies a risk for bacterial growth in foods. Consequently, high numbers of Bacillus spp. may occur after growth in some products. High numbers of cytotoxic Bacillus spp. in foods may represent a risk for food poisoning.

The hidden lifestyles of Bacillus cereus and relatives

Bacillus cereus sensu lato, the species group comprising Bacillus anthracis, Bacillus thuringiensis and B. cereus (sensu stricto), has previously been scrutinized regarding interspecies genetic correlation and pathogenic characteristics. So far, little attention has been paid to analysing the biological and ecological properties of the three species in their natural environments. In this review, we describe the B. cereus sensu lato living in a world on its own; all B. cereus sensu lato can grow saprophytically under nutrient-rich conditions, which are only occasionally found in the environment, except where nutrients are actively collected. As such, members of the B. cereus group have recently been discovered as common inhabitants of the invertebrate gut. We speculate that all members disclose symbiotic relationships with appropriate invertebrate hosts and only occasionally enter a pathogenic life cycle in which the individual species infects suitable hosts and multiplies almost unrestrained.

Properties of Bacillus thuringiensis isolated from bank voles

AIMS

To assess the properties of B. thuringiensis naturally occurring in the intestines of bank voles.

METHODS AND RESULTS

Seventeen Bacillus thuringiensis strains, exhibiting typical growth on selective medium for the B. cereus group and characterized by the ability to produce parasporal crystals, were isolated from bank voles trapped in the Łomza Landscape Park of the Narew River Valley (north-east Poland). All isolates were characterized by pulsed field gel electrophoresis (PFGE) of chromosomal DNA and SDS polyacrylamide gel electrophoresis (SDS-PAGE) of whole-cell proteins. Six pulsotypes were found with PFGE typing, using SmaI or NotI as restriction enzymes. Significant differences in chromosome size, ranging from 2.4 to 4.2 Mb for the B. thuringiensis strains studied, were noted. Strain heterogeneity in pulsotypes was also reflected by the similarity of whole-cell protein profiles of the strains. Environmental isolates and reference strains grouped at 71% similarity according to SDS-PAGE data and at 84% on the basis of biochemical tests.

CONCLUSIONS

B. thuringiensis from intestines of bank voles demonstrated an important level of heterogeneity. The comparison of PFGE profiles and SDS-PAGE of whole-cell protein patterns may be useful to evaluate the relationship between B. thuringiensis isolates.

SIGNIFICANCE AND IMPACT OF THE STUDY

The results presented in this paper may help to explain the diversity of B. thuringiensis.

Extremely high frequency of common flagellar antigens between Bacillus thuringiensis and Bacillus cereus

Bacillus cereus isolates, recovered from natural environments of Japan, were examined for their flagellar (H) antigenicities with the reference H antisera against Bacillus thuringiensis serotypes H1-H55. Of 236 B. cereus isolates tested, 165 (70%) were agglutinated with the reference antisera available. The frequencies of seropositive isolates were: 77% in soils, 68% on phylloplanes, and 60% in animal fecal populations. Among the 45 H serogroups detected, the serovar shandongiensis (H22) was the predominant, followed by the serovars entomocidus (H6), indiana (H16), pakistani (H13), and neoleonensis (H24ab). These five H serovars were commonly distributed in the three populations from different sources.

Isolation of Bacillus thuringiensis from intertidal brackish sediments in mangroves

Intertidal brackish sediments in mangroves were examined for isolation of Bacillus thuringiensis strains with novel toxicity spectra. A total of 18 B. thuringiensis isolates were recovered from eight sediment samples (36.4%) out of 22 samples tested. The frequency of B. thuringiensis was 1.3% among the colonies of Bacillus cereus/B. thuringiensis group. While five isolates were allocated to the four H serogroups, the majority of the isolates were serologically untypable or untestable. Two isolates belonging to the serovar israelensis/tochigiensis (H14/19) exhibited strong toxicities against larvae of the mosquito, Culex pipiens molestus, and mammalian cells (sheep erythrocyte and two human cancer cell lines) in vitro. The other 16 isolates showed no toxicity against the mosquito and mammalian cells. None of the isolates showed larvicidal activity against the diamondback moth, Plutella xylostella. Strong lectin activities against sheep erythrocytes were associated with two serologically untestable isolates and an H3 isolate.

In vitro cytotoxicity of non-cyt inclusion proteins of a Bacillus thuringiensis isolate against human cells, including cancer cells

A soil isolate designated 90-F-45-14, belonging to Bacillus thuringiensis serovar dakota (H15), was examined for characterization of in vitro cytotoxicity, associated with parasporal inclusion proteins, against human cells. When activated with proteolytic processing, inclusion proteins of the isolate 90-F-45-14 exhibited a moderate cytotoxicity against the human uterus cervix cancer cells (HeLa) with an EC(50) value of 60.8 microg ml(-1), while showing extremely high activities on the human leukaemic T cells (MOLT-4) and the normal T cells with EC(50) values of 0.27 and 0.20 microg ml(-1), respectively. Anti-leukaemic cell activity of the 90-F-45-14 proteins was eight to nine times greater than that of the B. thuringiensis serovar israelensis proteins containing the Cyt1 protein, a broad-spectrum cytolysin. The cytopathy by the 90-F-45-14 proteins was characterized by marked cell-ballooning, while the israelensis proteins induced early breakdown of the cells due to cytolysis. Inclusions of the isolate consisted of five major polypeptides of 170, 103, 73, 40 and 32 kDa. A 100% homology was observed in the sequence of 15 N-terminal amino acids between the proteins of 170 and 103 kDa. There was no N-terminal sequence homology between 90-F-45-14 proteins and the existing Cry/Cyt proteins of B. thuringiensis. Proteolytic processing by proteinase K yielded several proteins with molecular masses ranging from 40 to 28 kDa.

Noninsecticidal parasporal proteins of a Bacillus thuringiensis serovar shandongiensis isolate exhibit a preferential cytotoxicity against human leukemic T cells

A Bacillus thuringiensis isolate, 89-T-34-22, belonging to the serovar shandongiensis (H22) produced noninsecticidal and nonhemolytic proteins crystallizing into irregular-shaped parasporal inclusions. The proteins showed in vitro cytotoxicity to human cells, including cancer cells, only when activated by protease treatment. The human leukemic T (MOLT-4) cells were > 100 times more susceptible than HeLa and normal T cells to the proteins of 89-T-34-22. The cytotoxicity was dose dependent and the median effective concentration for the MOLT-4 was 3.5 microg/ml. The cytopathy induced by the 89-T-34-22 proteins was characterized by remarkable condensation of the nucleus and cell-ballooning. Five major parasporal proteins of 89-T-34-22, with molecular masses in the range of 16-160 kDa, shared no similarity with the previously reported proteins in terms of the N-terminal sequence.