Characterization of a cryptic plasmid pPZZ84 from Bacillus pumilus

The complete nucleotide sequence of a cryptic plasmid pPZZ84 from Bacillus pumilus strain ZZ84 was determined. Plasmid pPZZ84 is 6817 bp long with GC content of 36.7%. Seven putative open reading frames were identified. ORF7 shows 91% and 90% amino acid identity with rep proteins of pSH1452 and pPL1, respectively, members of rolling-circle replication (RCR) pC194-family. A typical pC194-family double strand origin (dso), a single-stranded origin (sso) and rap (regulator aspartate phosphatase) proteins were also identified in the plasmid. These results imply that pPZZ84 belongs to the Bacillus subtilis species group of small rolling circle (BsSRC) replicating plasmids. The plasmid copy number of pPZZ84 in B. pumilus ZZ84 was estimated to be 46 per cell, more than that of other BsSRC plasmids in their hosts.     

Cloning and molecular characterization of a novel rolling-circle replicating plasmid, pK1S-1, from Bacillus thuringiensis subsp. kurstaki K1

Bacillus thuringiensis, an entomopathogenic bacterium belonging to the B. cereus group, harbors numerous extra-chromosomal DNA molecules whose sizes range from 2 to 250 kb. In this study, we used a plasmid capture system (PCS) to clone three small plasmids from B. thuringiensis subsp. kurstaki Kl which were not found in B. thuringiensis subsp. kurstaki HD-1, and determined the complete nucleotide sequence of plasmid pKlS-1 (5.5 kb). Of the six putative open reading frames (ORF2-ORF7) in pKlS-1, ORF2 (MobKl) showed approximately 90% aa identity with the Mob-proteins of pGI2 and pTX14-2, which are rolling circle replicating group VII (RCR group VII) plasmids from B. thuringiensis. In addition, a putative origin of transfer (oriT) showed 95.8% identity with those of pGI2 and pTX14-2. ORF3 (RepK1) showed relatively low aa identity (17.8～25.2%) with the Rep protein coded by RCR plasmids, however. The putative double-strand origin of replication (dso) and single-strand origin of replication (sso) of pKlS-1 exhibited approximately 70% and 64% identities with those of pGI2 and pTX14-2. ORF6 and 7 showed greater than 50% similarities with alkaline serine protease, which belongs to the subtilase family. The other 2 ORFs were identified as hypothetical proteins. To determine the replicon of pKlS-1, seven subclones were contructed in the B. thuringiensis ori-negative pHTIK vector and were electroporated into a plasmid cured B. thuringiensis strain. The 1.6 kb region that included the putative ORF3 (ReplK), dso and ORF4, exhibited replication ability. These findings identified pKlS-1 as a new RCR group VII plasmid, and determined its replication region.     

Nucleotide sequence and characterization of the cryptic Bacillus thuringiensis plasmid pGI3 reveal a new family of rolling circle replicons.

The complete nucleotide sequence of plasmid pGI3 from Bacillus thuringiensis subsp. thuringiensis H1.1. was obtained. Although this 11,365-bp molecule contained at least 11 putative open reading frames (ORFs), extensive database searches did not reveal any homologous sequences with the exception of ORF6, which displayed similarity to the largest ORF of pSTK1, a 1,883-bp cryptic plasmid isolated from Bacillus stearothermophilus. Deletion analysis to determine the pGI3 minimal replicon revealed that ORF6 is the rep gene. Replication occurred via a single-stranded DNA (ssDNA) intermediate, as demonstrated by S1 treatment and Southern hybridization in nondenaturating conditions. Interestingly, however, no homology was found between the pGI3 (ORF6) and pSTK1 (ORF3) rep genes and those from other single-stranded DNA plasmids, nor was there any DNA similarity to the double-strand origins of replication characterized so far, indicating that pGI3 and pSTK1 form another, new family of ssDNA plasmids. PCR analysis revealed that the pGI3 rep gene is largely distributed among B. thuringiensis strains but can also be found in B. cereus and B. mycoides strains, albeit at a lower frequency. Finally, segregation experiments performed with B. subtilis and B. thuringiensis showed that the pGI3 derivatives, including the minimal replicon, were segregationally stable at temperatures suitable for B. thuringiensis growth (<43 degrees C).     

Replication Mechanism and Sequence Analysis of the Replicon of pAW63, a Conjugative Plasmid from Bacillus thuringiensis

A 5.8-kb fragment of the large conjugative plasmid pAW63 from Bacillus thuringiensis subsp. kurstaki HD73 containing all the information for autonomous replication was cloned and sequenced. By deletion analysis, the pAW63 replicon was reduced to a 4.1-kb fragment harboring four open reading frames (ORFs). Rep63A (513 amino acids [aa]), encoded by the largest ORF, displayed strong similarity (40% identity) to the replication proteins from plasmids pAMbeta1, pIP501, and pSM19035, indicating that the pAW63 replicon belongs to the pAMbeta1 family of gram-positive theta-replicating plasmids. This was confirmed by the facts that no single-stranded DNA replication intermediates could be detected and that replication was found to be dependent on host-gene-encoded DNA polymerase I. An 85-bp region downstream of Rep63A was also shown to have strong similarity to the origins of replication of pAMbeta1 and pIP501, and it is suggested that this region contains the bona fide pAW63 ori. The protein encoded by the second large ORF, Rep63B (308 aa), was shown to display similarity to RepB (34% identity over 281 aa) and PrgP (32% identity over 310 aa), involved in copy control of the Enterococcus faecalis plasmids pAD1 and pCF10, respectively. No significant similarity to known proteins or DNA sequences could be detected for the two smallest ORFs. However, the location, size, hydrophilicity, and orientation of ORF6 (107 codons) were analogous to those features of the putative genes repC and prgO, which encode stability functions on plasmids pAD1 and pCF10, respectively. The cloned replicon of plasmid pAW63 was stably maintained in Bacillus subtilis and B. thuringiensis and displayed incompatibility with the native pAW63. Hybridization experiments using the cloned replicon as a probe showed that pAW63 has similarity to large plasmids from other B. thuringiensis subsp. kurstaki strains and to a strain of B. thuringiensis subsp. alesti.     

A 20-kilodalton protein is required for efficient production of the Bacillus thuringiensis subsp. israelensis 27-kilodalton crystal protein in Escherichia coli.

The 27-kilodalton (kDa) mosquitocidal protein gene from Bacillus thuringiensis subsp. israelensis has been cloned as a 10-kilobase (kb) HindIII fragment from plasmid DNA; efficient expression in Escherichia coli KM1 depends on a region of DNA located approximately 4 kb upstream (K. McLean and H. R. Whiteley, J. Bacteriol. 169:1017-1023, 1987). We have cloned the upstream DNA region and show that it contains a complete open reading frame (ORF) encoding a protein with a molecular mass of 19,584 Da. Sequencing of adjacent stretches of DNA revealed two partial ORFs: one has 55.2% identity in an overlap of 319 amino acids to the putative transposase of IS231 of B. thuringiensis subsp. thuringiensis, and the other, a 78-codon partial ORF, may be the carboxyl terminus of the 67-kDa protein previously observed in maxicells of strain KM1. A 0.8-kb fragment containing only the 20-kDa protein gene greatly enhanced the expression of the 27-kDa protein in E. coli. The introduction of nonsense codons into the 20-kDa protein gene ORF abolished this effect, indicating that the gene product, not the mRNA or DNA, is required for the enhancement. The effect of the 20-kDa protein gene on various fusions of lacZ to the 27-kDa protein gene suggests that the 20-kDa protein acts after the initiation of translation of the 27-kDa protein gene.     

Sequencing and Characterization of Plasmid pUIBI-1 from <Emphasis Type="Italic">Bacillus thuringiensis</Emphasis> Serovar <Emphasis Type="Italic">entomocidus</Emphasis> LBIT-113

Plasmid pUIBI-1 from Bacillus thuringiensis svr. entomocidus was sequenced and its replication mechanism analyzed. Sequence analysis revealed that pUIBI-1 contains 4671 bp and a 32% GC content. Plasmid pUIBI-1 also includes at least seven putative open reading frames (ORFs) encoding for proteins ranging from 5 to 50 kDa. ORF-1 encodes for a putative 16-kDa Rep protein, which lacks homology with proteins of similar function. ORF2 encodes for a protein of 50 kDa and shows homology with Mob proteins of plasmids pLUB1000 from Lactobacillus hilgardii (32.2%) and pGI2 from B. thuringiensis (33.7%). Detection of single-stranded DNA (ssDNA) intermediates indicated that pUIBI-1 replicates by the rolling-circle replication mechanism, as demonstrated by S1 treatment and Southern hybridization under non-denaturing conditions.     

Expression of mosquitocidal crystal protein genes in non-insecticidal Bacillus thuringiensis subsp. israelensis

Bacillus thuringiensis NTB-1 isolated from soil samples in Korea produces ovoidal parasporal inclusions with proteins of approximately 24–40 kDa in size. Although serological study indicated that the isolate has a flagella (H) antigen identical with subsp. israelensis , it seemed to be non-insecticidal against Lepidoptera and Coleoptera as well as Diptera. To investigate the activity of non-insecticidal B. thuringiensis transformed with insecticidal crystal protein genes, cryIVD and cytA genes of B. thuringiensis subsp. morrisoni PG-14, highly toxic to mosquito larvae, were introduced into the isolate NTB-1. The expression of mosquitocidal crystal protein genes in NTB-1 was characterized by SDS–PAGE analysis and electron microscopy. The results showed that crystalline inclusions of host, CryIVD and CytA were stably expressed in the transformant. However, the mosquitocidal activity of transformant was similar to that of B. thuringiensis subsp. kurstaki Cry⁻ B harbouring cryIVD and cytA genes, demonstrating that a synergistic effect by an interaction of both introduced insecticidal and resident non-insecticidal crystal proteins was not observed.     

Isolation of Multiple Subspecies of Bacillus thuringiensis from a Population of the European Sunflower Moth, Homoeosoma nebulella

Five subspecies of Bacillus thuringiensis were isolated from dead and diseased larvae obtained from a laboratory colony of the European sunflower moth, Homoeosoma nebulella. The subspecies isolated were B. thuringiensis subspp. thuringiensis (H 1a), kurstaki (H 3a3b3c), aizawai (H 7), morrisoni (H 8a8b), and thompsoni (H 12). Most isolates produced typical bipyramidal crystals, but the B. thuringiensis subsp. thuringiensis isolate produced spherical crystals and the B. thuringiensis subsp. thompsoni isolate produced a pyramidal crystal. Analysis of the parasporal crystals by sodium dodecyl sulfate-polyacrylamide gel electrophoresis showed that the crystals from the B. thuringiensis subsp. kurstaki and aizawai isolates contained a protein of 138 kDa whereas those from B. thuringiensis subsp. morrisoni contained a protein of 145 kDa. The crystals from B. thuringiensis subsp. thuringiensis contained proteins of 125, 128, and 138 kDa, whereas those from B. thuringiensis subsp. thompsoni were the most unusual, containing proteins of 37 and 42 kDa. Bioassays of purified crystals conducted against second-instar larvae of H. nebulella showed that the isolates of B. thuringiensis subspp. aizawai, kurstaki, and thuringiensis were the most toxic, with 50% lethal concentrations (LC(inf50)s) of 0.15, 0.17, and 0.26 (mu)g/ml, respectively. The isolates of B. thuringiensis subspp. morrisoni and thompsoni had LC(inf50)s of 2.62 and 37.5 (mu)g/ml, respectively. These results show that a single insect species can simultaneously host and be affected by a variety of subspecies of B. thuringiensis producing different insecticidal proteins.     

Characterization of a cryptic plasmid from an alpha-proteobacterial endosymbiont of Amoeba proteus

A new cryptic plasmid pAP3.9 was discovered in symbiotic alpha-proteobacteria present in the cytoplasm of Amoeba proteus. The plasmid is 3869bp with a GC content of 34.66% and contains replication origins for both double-strand (dso) and single-strand (sso). It has three putative ORFs encoding Mob, Rep and phosphoglycolate phosphatase (PGPase). The pAP3.9 plasmid appears to propagate by the conjugative rolling-circle replication (RCR), since it contains all required factors such as Rep, sso and dso. Mob and Rep showed highest similarities to those of the cryptic plasmid pBMYdx in Bacillus mycoides. The PGPase was homologous to that of Bacillus cereus and formed a clade with those of Bacillus sp. in molecular phylogeny. These results imply that the pAP3.9 plasmid evolved by the passage through Bacillus species. We hypothesize that the plasmid-encoded PGPase may have contributed to the establishment of bacterial symbiosis within the hostile environment of amoeba cytoplasm.     

Insecticidal toxins from Bacillus thuringiensis subsp. kenyae: gene cloning and characterization and comparison with B. thuringiensis subsp. kurstaki CryIA(c) toxins

Genes encoding insecticidal crystal proteins were cloned from three strains of Bacillus thuringiensis subsp. kenyae and two strains of B. thuringiensis subsp. kurstaki. Characterization of the B. thuringiensis subsp. kenyae toxin genes showed that they are most closely related to cryIA(c) from B. thuringiensis subsp. kurstaki. The cloned genes were introduced into Bacillus host strains, and the spectra of insecticidal activities of each Cry protein were determined for six pest lepidopteran insects. CryIA(c) proteins from B. thuringiensis subsp. kenyae are as active as CryIA(c) proteins from B. thuringiensis subsp. kurstaki against Trichoplusia ni, Lymantria dispar, Heliothis zea, and H. virescens but are significantly less active against Plutella xylostella and, in some cases, Ostrinia nubilalis. The sequence of a cryIA(c) gene from B. thuringiensis subsp. kenyae was determined (GenBank M35524) and compared with that of cryIA(c) from B. thuringiensis subsp. kurstaki. The two genes are more than 99% identical and show seven amino acid differences among the predicted sequences of 1,177 amino acids.     

A novel cryptic plasmid pBMB175 from <Emphasis Type="Italic">Bacillus thuringiensis </Emphasis>subsp. <Emphasis Type="Italic">tenebrionis </Emphasis>YBT-1765

A new cryptic plasmid pBMB175 from Bacillus thuringiensis subsp. tenebrionis YBT-1765 was isolated and characterized. Sequence analysis showed that pBMB175 (14,841 bp and 31% GC content) contained at least eighteen putative open reading frames (ORFs), among which nine ORFs displayed the homology with the hypothetical proteins in rolling-circle replication plasmid pGI3. Deletion analysis revealed that the pBMB175 minireplicon located in a novel 1,151 bp fragment. This fragment contains ORF7 coding sequence, which encodes a protein (Rep175, 149 amino acids [aa]) indispensable for plasmid replication. Rep175 has no significant homology with known function proteins. Furthermore, a putative double-strand origin (dso), having no DNA similarity with characterized dso of other replicon so far, was identified in this minireplicon fragment. These features showed that pBMB175 could be placed into a new plasmid family.     

Molecular characterization of two novel crystal protein genes from Bacillus thuringiensis subsp. thompsoni.

Two genes encoding the predominant polypeptides of Bacillus thuringiensis subsp. thompsoni cuboidal crystals were cloned in Escherichia coli and sequenced. The polypeptides have electrophoretic mobilities of 40 and 34 kDa, with the deduced amino acid sequences predicting molecular masses of 35,384 and 37,505 Da, respectively. No statistically significant similarities were detected between the 40- or 34-kDa crystal protein and any other characterized B. thuringiensis crystal protein, nor were they detected between the 40- and 34-kDa crystal proteins. A 100-MDa plasmid carries both crystal protein genes, which appear to be part of an operon, with the 40-kDa gene 64 nucleotides upstream of the 34-kDa gene. Both crystal proteins are synthesized in approximately the same amounts. Even though small compared with other crystal proteins, the 34-kDa crystal protein has insecticidal activity against lepidopteran larvae (Manduca sexta). The 40-kDa polypeptide appears to have no insecticidal activity, but it could have a role in crystal structure.     

Conjugative transfer, stability and expression of a plasmid encoding a cry1Ac gene in Bacillus cereus group strains

The plasmid pHT73 containing cry1Ac and tagged with an erythromycin resistance gene was transferred from Bacillus thuringiensis subspecies kurstaki KT0 to several Bacillus cereus group strains by conjugation. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and phase contrast microscopy showed that the transconjugants containing plasmid pHT73 could express Cry1Ac toxin and produce bipyramidal crystalline inclusion bodies during sporulation. The study demonstrated that pHT73 could be transferred to B. thuringiensis subsp. kurstaki, several B. cereus strains and Bacillus mycoides. Under non-selective conditions, the stability of the pHT73 plasmid in the transconjugants was found to be 58.2-100% after 100 generations and 4-96% after 200 generations. The variations are mainly caused by the choice of receptor strain.     

The patchwork nature of rolling-circle plasmids: comparison of six plasmids from two distinct Bacillus thuringiensis serotypes

Bacillus thuringiensis, the entomopathogenic bacteria from the Bacillus cereus group, harbors numerous extrachromosomal molecules whose sizes vary from 2 to more than 200kb. Apart from the genes coding for the biopesticide delta-endotoxins located on large plasmids, little information has been obtained on these plasmids and their contribution to the biology of their host. In this paper, we embarked on a detailed comparison of six small rolling-circle replicating (RCR) plasmids originating from two major B. thuringiensis strains. The complete nucleotide sequences of plasmid pGI1, pGI2, pGI3, pTX14-1, pTX14-2, and pTX14-3 have been obtained and compared. Replication functions, comprising, for each plasmid, the gene encoding the Rep-protein, double-strand origin of replication (dso), single-strand origin of replication (sso), have been identified and analyzed. Two new families, or homology groups, of RCR plasmids originated from the studies of these plasmids (Group VI based on pGI3 and Group VII based on pTX14-3). On five of the six plasmids, loci involved in conjugative mobilization (Mob-genes and origin of transfer (oriT)) were identified. Plasmids pTX14-1, pTX14-2, and pTX14-3 each harbor an ORF encoding a polypeptide containing a central domain with repetitive elements similar to eukaryotic collagen (Gly-X-Y triplets). These genes were termed bcol for Bacillus-collagen-like genes.     

Expression of the insecticidal protein gene from Bacillus thuringiensis subsp. aizawai in Bacillus subtilis and in the thermophile Bacillus stearothermophilus by using the alpha-amylase promoter of the thermophile

Expression of the insecticidal protein gene from Bacillus thuringiensis subsp. aizawai IPL7 in B. subtilis MI113 and B. stearothermophilus SIC1 was examined. Production of the protein (130 kilodaltons [KDa]) was analyzed by its reaction with antibody against the insecticidal proteins of the parental B. thuringiensis. When the original gene containing its own promoter was subcloned in B. subtilis, only a small amount of the protein was produced. Therefore, both the promoter for the B. stearothermophilus alpha-amylase gene and the insecticidal protein gene were inserted in a repA (low-copy-number) plasmid to yield the recombinant plasmid pTBT-Pamy. B. subtilis MI113 carrying pTBT-Pamy produced more of the 130-kDa protein (about 10(4) molecules per cell) at 37 degrees C. In contrast, B. stearothermophilus SIC1 carrying pTBT-Pamy produced a small amount of 130-kDa protein (10(2) to 10(3) molecules per cell) at 55 degrees C.     

Novel Bacillus thuringiensis binary insecticidal crystal proteins active on western corn rootworm, Diabrotica virgifera virgifera LeConte

A new family of insecticidal crystal proteins was discovered by screening sporulated Bacillus thuringiensis cultures for oral activity against western corn rootworm (WCR) larvae. B. thuringiensis isolates PS80JJ1, PS149B1, and PS167H2 have WCR insecticidal activity attributable to parasporal inclusion bodies containing proteins with molecular masses of ca. 14 and 44 kDa. The genes encoding these polypeptides reside in apparent operons, and the 14-kDa protein open reading frame (ORF) precedes the 44-kDa protein ORF. Mutagenesis of either gene in the apparent operons dramatically reduced insecticidal activity of the corresponding recombinant B. thuringiensis strain. Bioassays performed with separately expressed, biochemically purified 14- and 44-kDa polypeptides also demonstrated that both proteins are required for WCR mortality. Sequence comparisons with other known B. thuringiensis insecticidal proteins failed to reveal homology with previously described Cry, Cyt, or Vip proteins. However, there is evidence that the 44-kDa polypeptide and the 41.9- and 51.4-kDa binary dipteran insecticidal proteins from Bacillus sphaericus are evolutionarily related. The 14- and 44-kDa polypeptides from isolates PS80JJ1, PS149B1, and PS167H2 have been designated Cry34Aa1, Cry34Ab1, and Cry34Ac1, respectively, and the 44-kDa polypeptides from these isolates have been designated Cry35Aa1, Cry35Ab1, and Cry35Ac1, respectively.     

Unique regulation of crystal protein production in Bacillus thuringiensis subsp. yunnanensis is mediated by the cry protein-encoding 103-megadalton plasmid.

In sporulating cultures of Bacillus thuringiensis subsp. yunnanensis HD977, two cell types are observed: cells forming only spores and cells forming only crystals. Curing analysis suggested that the crystal proteins are plasmid encoded. Through plasmid transfer experiments, it was established that a 103-MDa plasmid is involved in the crystal production. Conjugal transfer of this plasmid to Cry- recipient cells of Bacillus thuringiensis subsp. kurstaki HD73-26 conferred the ability to produce crystals exclusively on asporogenous cells of the recipient, indicating that the 103-MDa plasmid mediates the unique regulation of Cry protein production. When the dipteran-specific cryIVB gene was introduced into wild-type (Cry+) and Cry- backgrounds of B. thuringiensis subsp. yunnanensis by phage CP51ts45-mediated transduction, similar to all other B. thuringiensis strains, irregular crystals of CryIVB protein were produced by spore-forming cells in both backgrounds. However, the synthesis of the bipyramidal inclusions of B. thuringiensis subsp. yunnanensis was still limited only to asporogenous cells of the transductant. Thus, it appears that the unique property of exclusive crystal formation in asporogenous cells of B. thuringiensis subsp. yunnanensis is associated with the crystal protein gene(s) per se or its cis acting elements. As the crystals in B. thuringiensis subsp. yunnanensis were formed only in asporogenous cells, attempts were made to find out whether crystal formation had any inhibitory effect on sporulation. It was observed that both Cry+ and Cry- strains of B. thuringiensis subsp. yunnanensis (HD977 and HD977-1, respectively) exhibited comparable sporulation efficiencies. In addition, the Cry- B. thuringiensis subsp. kurstaki host (HD73-26) and its Cry+ transconjugant (HD73-26-16), expressing the B. thuringiensis subsp. yunnanensis crystal protein, were also comparable in their sporulation efficiencies, indicating that production of the crystal proteins of B. thuringiensis subsp. yunnanensis does not affect the process of sporulation.