Assessment of the Antimicrobial Activity and the Entomocidal Potential of Bacillus thuringiensis Isolates from Algeria

Unraveling the abundance of vip3-type genes in Indian Bacillus thuringiensis across the agroclimatic landscape and impact of amino acid substitutions for safer agriculture

Vegetative insecticidal protein (vip) genes of Bacillus thuringiensis (Bt) are candidates for gene pyramiding in the resistance management of pests. The prevalence of vip genes in Bt isolates is relatively under-explored. Bt isolates recovered from 29 diverse sources in nine agro-climatic zones of India were screened for the presence of vip3-type genes by PCR with 4 sets of oligonucleotide primers. Out of 155 Bt isolates, 70.32 % (109) and 44.52 % (69) isolates were positive for amplification of partial vip3-type genes with primer sets 1 and 4, respectively. The primer set-2 was found to be more efficient for amplifying full-length genes (29.03 % /45 isolates) as compared with primer set-3 (3.23 %/ 5 isolates), also corroborated in the amplification of full-length vip3 genes in ten Bt BGSC strains used as reference. Frequency analysis revealed presence of vip3 genes in Bt isolates across all agro-climatic zones. Thus, Indian Bt isolates from diverse sources have a rich repertoire of vip3-type genes. Our study reports the highest number (45) of full-length vip3-type genes detected in a native Bt isolates collection, demonstrating enrichment of Indian Bt isolates for vip3 genes. Twelve of these genes have been cloned, sequenced, and out of these, six were found to be effective against Helicoverpa armigera in our laboratory previously. Comparison of substitutions in deduced amino acids sequence of these genes and expression of Vip3 proteins in SDS-PAGE analysis of selected native Bt isolates positive for full-length vip3-type genes indicated their biopesticidal potential.

Genome mining of Bacillus thuringiensis strain SY49.1 reveals novel candidate pesticidal and bioactive compounds

BACKGROUND

Bacillus thuringiensis SY49.1 (Bt SY49.1) strain has promising insecticidal and fungicidal activity against phytopathogens and pests. Therefore, we selected this strain for whole-genome sequencing (WGS), annotation and analysis, with the aim of identifying genes responsible for producing putative pesticidal toxins, antimicrobial metabolites and plant growth-promoting features.

RESULTS

Our results showed that the SY49.1 genome is 6. 32 Mbp long with a GC content of 34.68%. Genome mining revealed the presence of multiple gene inventories for the biosynthesis of bioactive compounds such as insecticidal delta endotoxins, secondary metabolites, and several plant growth-promoting proteins. Multiple sequence alignment revealed residue variations in the toxic core of Cry1Ab when compared with known Cry1Ab sequences from Bt nomenclature databases. This suggests that the cry1Ab of SY49.1 is a new kind of its group. Among the predicted secondary metabolites, we found a kurstakin with a predicted peptide that differs from the known kurstakin peptide available in the NORINE database. In addition, lipopeptides extracted from SY49.1 suppressed the growth of Verticillium dahliae and Fusarium oxysporum.

CONCLUSION

We anticipate that the complete genome of Bt SY49.1 may provide a model for properly understanding and studying antimicrobial compound mining, genetic diversity among the B. cereus group, and pathogenicity against insects. This is the first report on the WGS and mining of the Bt strain isolated from Turkey. © 2024 The Author(s). Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Searching for Chemical Agents Suppressing Substrate Microbiota in White-Rot Fungi Large-Scale Cultivation

Edible fungi are a valuable resource in the search for sustainable solutions to environmental pollution. Their ability to degrade organic pollutants, extract heavy metals, and restore ecological balance has a huge potential for bioremediation. They are also sustainable food resources. Edible fungi (basidiomycetes or fungi from other divisions) represent an underutilized resource in the field of bioremediation. By maximizing their unique capabilities, it is possible to develop innovative approaches for addressing environmental contamination. The aim of the present study was to find selective chemical agents suppressing the growth of microfungi and bacteria, but not suppressing white-rot fungi, in order to perform large-scale cultivation of white-rot fungi in natural unsterile substrates and use it for different purposes. One application could be the preparation of a matrix composed of wooden sleeper (contaminated with PAHs) and soil for further hazardous waste bioremediation using white-rot fungi. In vitro microbiological methods were applied, such as, firstly, compatibility tests between bacteria and white-rot fungi or microfungi, allowing us to evaluate the interaction between different organisms, and secondly, the addition of chemicals on the surface of a Petri dish with a test strain of microorganisms of white-rot fungi, allowing us to determine the impact of chemicals on the growth of organisms. This study shows that white-rot fungi are not compatible to grow with several rhizobacteria or bacteria isolated from soil and bioremediated waste. Therefore, the impact of several inorganic materials, such as lime (hydrated form), charcoal, dolomite powder, ash, gypsum, phosphogypsum, hydrogen peroxide, potassium permanganate, and sodium hydroxide, was evaluated on the growth of microfungi (sixteen strains), white-rot fungi (three strains), and bacteria (nine strains) in vitro. Charcoal, dolomite powder, gypsum, and phosphogypsum did not suppress the growth either of microfungi or of bacteria in the tested substrate, and even acted as promoters of their growth. The effects of the other agents tested were strain dependent. Potassium permanganate could be used for bacteria and Candida spp. growth suppression, but not for other microfungi. Lime showed promising results by suppressing the growth of microfungi and bacteria, but it also suppressed the growth of white-rot fungi. Hydrogen peroxide showed strong suppression of microfungi, and even had a bactericidal effect on some bacteria, but did not have an impact on white-rot fungi. The study highlights the practical utility of using hydrogen peroxide up to 3% as an effective biota-suppressing chemical agent prior to inoculating white-rot fungi in the large-scale bioremediation of polluted substrates, or in the large-scale cultivation for mushroom production as a foodstuff.

The use of antigens derived from Bacillus thuringiensis bacteria for further differentiation

This study is devoted to studying Bacillus thuringiensis antigens and their insecticide activity as critical features in bacterial differentiation. Indeed, 190 samples were examined for flagellar antigenicity as well as the insecticidal activity exhibited. From a serological perspective, 122 isolates (64.2 %) were attributed to 8 H-serogroups, including 3 non-typeable and 65 unverified. The dominant serotype was H3abc (82 % frequency); H6 was less frequent (8.5 %). The other 6 serotypes accounted for a low frequency of occurrence (up to 1.5 %). Of the 190 isolates tested, 125 (65.8 %) formed bipyramidal, and 63 (33.2 %) represented spherical inclusions. All H3abc isolates contained bipyramidal inclusions. The same applied to H8ab and H7 isolates. Insecticide activity was noted in 70.1 % of the population. In general, 128 samples were toxic to both species (Bombyx mori, Aedes sp.). Another 3 samples were toxic only to B. mori, and 2 for Aedes sp. Among the samples exhibiting toxicity to both species, 97.6 % belonged to bipyramidal paraspore inclusions (H3abc). All H7 samples were toxic to two insect species. Monotoxic B. thuringiensis against Aedes sp. were found only among organisms producing spherical parasporal inclusions in the cell. Examples of such microorganisms include an isolate of the H4ab/43 serotype.

Biological Control of Fusarium oxysporum, the Causal Agent of Fusarium Basal Rot in Onion by Bacillus spp

Fusarium oxysporum is the main pathogen causing Fusarium basal rot in onion (Allium cepa L.), which incurs significant yield losses before and after harvest. Among management strategies, biological control is an environmentally safe and sustainable alternative to chemical control. In this study, we isolated and screened bacteria for antifungal activity against the basal rot pathogen F. oxysporum. Isolates 23-045, 23-046, 23-052, 23-055, and 23-056 significantly inhibited F. oxysporum mycelial growth and conidial germination. Isolates 23-045, 23-046, 23-052, and 23-056 suppressed the development of Fusarium basal rot in both onion seedlings and bulbs in pot and spray inoculation assays. Isolate 23-055 was effective in onion seedlings but exhibited weak inhibitory effect on onion bulbs. Based on analyses of the 16S rRNA and rpoB gene sequences together with morphological analysis, isolates 23-045, 23-046, 23-052, and 23-055 were identified as Bacillus thuringiensis, and isolate 23-056 as Bacillus toyonensis. All five bacterial isolates exhibited cellulolytic, proteolytic, and phosphate-solubilizing activity, which may contribute to their antagonistic activity against onion basal rot disease. Taken together B. thuringiensis 23-045, 23-046, 23-052, and 23-055 and B. toyonensis 23-056 have potential for the biological control of Fusarium basal rot in onion.

More than just an insect killer: The non-insecticidal activities of Bacillus thuringiensis with biotechnological potential

Bacillus thuringiensis (Bt) is known for the biological control of important insect pests, but scientific advances have revealed several interesting characteristics, in addition to this classical function as a bioinsecticide. To investigate the current knowledge about these non-insecticidal activities, a systematic research on primary data in the scientific literature was conducted on alternative functions of Bt with biotechnological potential. Out of a total of 140 articles selected, 15 non-insecticidal Bt activities were found. Publications related to this topic are available since 1971, and different metadata were reported, such as biomolecules and genes involved in Bt performances in non-insecticidal bioactivities. A total of 11 Bt activities with different effect measures (response variables) were identified, with an average of 48 distinct Bt strains evaluated per activity. Approximately 81.2% of all identified experiments/tests deal with the direct effects of Bt on target cells/organisms, with 36.3% of the strains within these studies tested for antibacterial action; of all microbial targets tested, 92.8% are bacteria, which led to 75.2% of the experimental conditions for all direct activities being performed in vitro. Regarding indirect Bt activities, 67.6% of these studies reported tritrophic Bt-plant-pathogen interactions. Bioremediation also appears as a relevant Bt activity being investigated in-depth. Alternative Bt activities offer innovative ways of developing biotechnology for different areas of anthropic interest; hence, we also focus on the possibility of finding multifunctional strains of Bt, as this may be advantageous from a bioeconomic point of view. Our findings are discussed in terms of research trends, aspects, details and depth of the current knowledge on alternative non-insecticidal Bt traits. We also discuss the potential application of this science for useful technological developments, aiming at solving issues related to human health, sustainable agriculture and environmental preservation/restoration.

Multiple cry Genes in Bacillus thuringiensis Strain BTG Suggest a Broad-Spectrum Insecticidal Activity

The properties of Bacillus thuringiensis strains as a biopesticide with potent action against moths, beetles, and mosquitoes have been known for decades, with individual subspecies showing specific activity against a particular pest. The aim of the present work is to characterize strains that can be used for broad-spectrum pest control in agriculture. Twenty strains of B. thuringiensis were isolated from Bulgarian soil habitats. The strains were screened for genes encoding 12 different crystal (Cry) endotoxins by PCR with specific primer pairs. Seven of the isolates contained cry genes in their genomes. B. thuringiensis strains PL1, PL3, and PL20 contained at least three different cry genes, while B. thuringiensis serovar galleriae BTG contained at least four. Moreover, scanning electron microscopy (SEM) investigation revealed the production of bipyramidal (PL1, PL3, PL20), polygonal (PL1), cubic (BTG), and spherical crystals (BTG and PL20). Potentially containing the most cry genes, the BTG genome was sequenced and annotated. It comprises 6,275,416 base pairs, does not contain plasmids, has a GC content of 35.05%, and contained 7 genes encoding crystal toxins: cry1Ab35, cry1Db, cry1Fb, cry1Ib, cry2Ab, cry8Ea1, and cry9Ba. This unique combination would possibly enable the simultaneous pesticidal action against pest species from orders Lepidoptera, Coleoptera, Diptera, and Hemiptera, as well as class Gastropoda. Whole-genome sequencing provided accurate information about the presence, localization, and classification of Cry toxins in B. thuringiensis BTG, revealing the great potential of the strain for the development of new broad-spectrum bio-insecticides.

Bacillus thuringiensis-Based Bioproduct: Characterization and Performance Against Spodoptera frugiperda Strains in Maize Under Different Environmental Temperatures

Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae) is an important pest in several regions being the use of Bacillus thuringiensis-based bioproducts an alternative for its control. Firstly, 3 L of an aqueous bioproduct suspension was produced and characterized. Its 50% lethal concentration against molecularly identified corn and rice S. frugiperda strains using an artificial diet were 77.01% (95% CL, 68.16-90.47) and 2.22% (95% CL, 0.01-6.68), respectively. The next objective of this work was to evaluate the performance of this bioproduct in maize against S. frugiperda strains under different simulated agrological regions mimicking their corresponding periodic day/night temperatures. Thus, the impact of environmental temperature on the bioproduct efficacy (E) was studied. It was observed that a warmer scenario (35 °C day/30 °C night) could favor the tolerance of corn S. frugiperda strain to the bioproduct (E = 56.36 ± 0.61%) maintaining a high efficacy (92.44 ± 6.55%) when it was tested against rice S. frugiperda strain. Conversely, under temperate conditions, efficacy values ranged from 84 to 95% for both S. frugiperda strains. On the other hand, based on a foliar feeding damage analysis, our bioproduct displayed a significant foliar protection in maize plants infested with either corn or rice S. frugiperda strains.

Abundance, distribution, and expression of nematicidal crystal protein genes in Bacillus thuringiensis strains from diverse habitats

Bacillus thuringiensis (Bt) is a Gram-positive bacterium that accumulates pesticidal proteins (Cry and Cyt) in parasporal crystals. Proteins from the Cry5, App6 (formerly Cry6), Cry12, Cry13, Cry14, Cry21, and Xpp55 (formerly Cry55) families have been identified as toxic to nematodes. In this study, a total of 846 Bt strains belonging to four collections were analyzed to determine the diversity and distribution of the Bt Cry nematicidal protein genes. We analyzed their presence by PCR, and positives were confirmed by sequencing. As a result, 164 Bt isolates (20%) contained at least one gene coding for nematicidal Cry proteins. The cry5 and cry21 genes were enriched in collection 1 and were often found together in the same strain. Differently, in collection 4, obtained from similar habitats but after 10 years, cry14 was the gene most frequently found. In collection 2, cry5 and app6 were the most abundant genes, and collection 3 had a low incidence of any of these genes. The results point to high variability in the frequencies of the studied genes depending on the timing, geographical origins, and sources. The occurrence of cry1A, cry2, and cry3 genes was also analyzed and showed that the nematicidal Cry protein genes were frequently accompanied by cry1A + cry2. The expression of the genes was assessed by mass spectrometry showing that only 14% of the positive strains produced nematicidal proteins. To our knowledge, this is the first comprehensive screening that examines the presence and expression of genes from the seven known Bt Cry nematicidal families.

Quorum quenching and anti-biofilm activities of halotolerant Bacillus strains isolated in different environments in Algeria

AIMS

The current study aimed to screen Bacillus strains with wide-spectrum quorum quenching (QQ) activity against N-acyl-l-homoserine lactones (AHLs), helpful in controlling virulence traits in Gram-negatives, including biofilm formation and also with anti-biofilm activity against Gram-positives.

METHODS AND RESULTS

A total of 94 halotolerant strains of Bacillus isolated from soil and salt-lake sediment samples in Algeria were examined for the presence of QQ activity against AHLs, the presence of the aiiA gene, encoding an AHL lactonase enzyme typical of Bacillus spp., antimicrobial and anti-biofilm activities against Pseudomonas aeruginosa and Streptococcus mutans. Of all strains of Bacillus spp. isolated, 48.9% showed antibacterial activity. In addition, 40% of these isolates showed a positive QQ activity against long-chain AHLs, of which seven strains presented the aiiA gene. Among the species with broad-spectrum QQ activity, the cell extract of Bacillus thuringiensis DZ16 showed antibiofilm activity against P. aeruginosa PAO1, reducing 60% using the Amsterdam active attachment (AAA) biofilm cultivation model. In addition, the cell extract of B. subtilis DZ17, also presenting a broad-spectrum QQ activity, significantly reduced Strep. mutans ATCC 25175 biofilm formations by 63% and 53% in the xCELLigence and the AAA model, respectively, without affecting growth. Strain DZ17 is of particular interest due to its explicit halophilic nature because it can thrive at salinities in the range of 6%-30%.

CONCLUSIONS

B. thuringiensis DZ16 and B. subtilis DZ17 strains have interesting antibacterial, QQ, and anti-biofilm activities. The high range of salinities accepted by these strains increases their biotechnological potential. This may open up their use as probiotics, the treatment and prevention of conventional and emerging infectious diseases.

SIGNIFICANCE AND IMPACT OF STUDY

The use of safe, economical and effective probiotics is limited to control the infections related to multi-resistant bacteria. In our study, we provide two promising agents with QQ, anti-biofilm and antibacterial activities.

Microbial chitinases: properties, enhancement and potential applications

Chitinases are a category of hydrolytic enzymes that catalyze chitin and are formed by a wide variety of microorganisms. In nature, microbial chitinases are primarily responsible for chitin decomposition and play a vital role in the balance of carbon and nitrogen ratio in the ecosystem. The physicochemical attributes and the source of chitinase are the main bases that determine their functional characteristics and hydrolyzed products. Several chitinases have been reported and characterized, and they obtain a wider consideration for their utilization in a large number of uses such as in agriculture, food, environment, medicine and pharmaceutical companies. The antifungal and insecticidal impacts of several chitinases have been extensively studied, aiming to protect crops from phytopathogenic fungi and insects. Chitooligosaccharides synthesized by chitin degradation have been shown to improve human health through their antimicrobial, antioxidant, anti-inflammatory and antitumor properties. This review aims at investigating chitinase production, properties and their potential applications in various biotechnological fields.

Vegetative Insecticidal Protein (Vip): A Potential Contender From Bacillus thuringiensis for Efficient Management of Various Detrimental Agricultural Pests

Bacillus thuringiensis (Bt) bacterium is found in various ecological habitats, and has natural entomo-pesticidal properties, due to the production of crystalline and soluble proteins during different growth phases. In addition to Cry and Cyt proteins, this bacterium also produces Vegetative insecticidal protein (Vip) during its vegetative growth phase, which is considered an excellent toxic candidate because of the difference in sequence homology and receptor sites from Cry proteins. Vip proteins are referred as second-generation insecticidal proteins, which can be used either alone or in complementarity with Cry proteins for the management of various detrimental pests. Among these Vip proteins, Vip1 and Vip2 act as binary toxins and have toxicity toward pests belonging to Hemiptera and Coleoptera orders, whereas the most important Vip3 proteins have insecticidal activity against Lepidopteran pests. These Vip3 proteins are similar to Cry proteins in terms of toxicity potential against susceptible insects. They are reported to be toxic toward pests, which can’t be controlled with Cry proteins. The Vip3 proteins have been successfully pyramided along with Cry proteins in transgenic rice, corn, and cotton to combat resistant pest populations. This review provides detailed information about the history and importance of Vip proteins, their types, structure, newly identified specific receptors, and action mechanism of this specific class of proteins. Various studies conducted on Vip proteins all over the world and the current status have been discussed. This review will give insights into the significance of Vip proteins as alternative promising candidate toxic proteins from Bt for the management of pests in most sustainable manner.

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.

Application of Optimized and Validated Agar Overlay TLC-Bioautography Assay for Detecting the Antimicrobial Metabolites of Pharmaceutical Interest

The agar overlay TLC-bioautography is one of the crucial methods for simultaneous in situ detection and separation of antimicrobial metabolites of pharmaceutical interest. The main focus of this research relies on the dereplication of an antimicrobial metabolite coriloxin derived from mycoendophytic Xylaria sp. NBRTSB-20 with a validation of agar overlay TLC-bioautography technique. This polyketide metabolite coriloxin was purified by column chromatography, and its purity was assessed by HPLC, UPLC-ESI-QTOF-MS, FT-IR and NMR spectral analysis. The antimicrobial capability of ethyl acetate extract and the purified compound coriloxin was determined by disc diffusion, minimal inhibitory concentration and agar overlay TLC-bioautography assay. The visible LOD of coriloxin antimicrobial activity was found at 10 μg for Escherichia coli and 20 μg for both Staphylococcus aureus and Fusarium oxysporum. Inter- and intra-day precision was determined as the relative standard deviation is less than 6.56%, which proved that this method was precise. The accuracy was expressed as recovery, and the values were found ranging from 91.18 to 108.73% with RSD values 0.94-2.30%, respectively. The overall findings of this investigation suggest that agar overlay TLC-bioautography assay is a suitable and acceptable method for the in situ determination of antimicrobial pharmaceuticals.

Toxicity evaluation of Aphidicidal crystalliferous toxins from Bacillus thuringiensis strains: a molecular study

Purpose

Aphis gossypii and A. punicae are the most damaging pests. The emergence of large populations has created concern among farmers because this pest complex is considered critical as it has a significant effect on major crops around the globe. The lack of new technologies for the control of A. gossypii and A. punicae is also worrying due to the indiscriminate use of chemical insecticides. Besides, this leads to the rapid development of resistance, which strangles their control in the field. Hence, there is a dire need to find the effective biocontrol agent for the management of Aphis gossypii and A. punicae.

Methods

The present investigation emphasizes the isolation and characterization of Aphidicidal Bacillus thuringiensis from the Andaman and Nicobar Islands, Karnataka, Assam, Arunachal Pradesh, and Sikkim soil samples. Phase contrast and scanning electron microscopy analysis used to characterize and identify the crystal morphology. Molecular profiling of Bt cry genes was determined by PCR using aphidicidal cry gene-specific primers, and molecular cloning and sequencing were carried out. Protein profiling by SDS–PAGE analysis was further studied. Finally, a qualitative bioassay of insecticidal activity was carried out against A. gossypii and A. punicae.

Results

A total of 65 Bacillus-like colonies were screened; 15 putative Aphidicidal B. thuringiensis isolates were identified based on morphological as well as through microbiological studies. Spherical and amorphous crystal inclusion was predominantly present in 34.28% of the Bt isolates. Crystal protein profiling of Bt isolates by SDS–PAGE analysis showed the presence 130, 73, 34, 25, and 13 kDa bands, among which 50−66 kDa bands were present abundantly. The detection of the cry gene of these isolates was done by PCR analysis, which indicated that cry1, cry2A, cry3A, and cry11A were on plasmid DNA. All cry genes were 80–100% homologous when aligned on alignment tool NCBI-BLASTn and BLASTp. All isolates of Bt were tested for their insecticidal activity against aphids. Three of the 15 isolates are Aphidicidal toxin specific by PCR analysis which were observed to be toxic to Aphis gossypii and A. punicae at a concentration of 35 μg/mL. The observed physical changes were induced by B. thuringiensis infection; these strains had been re-isolated from the dead aphids, and the presented results fulfilled Koch’s postulates.

Conclusion

The present study brought promising Bt isolates, primarily capable of creating an efficient biocontrol agent for Aphis gossypii and A. punicae and various sucking pests soon.

Evaluation of the Toxicity of Supernatant Cultures and Spore-Crystal Mixtures of Bacillus thuringiensis Strains Isolated from Algeria

Bacillus thuringiensis (Bt) is the most used technology for biological control of insect pathogens worldwide. In order to select new Bt candidates challenging the emergence of insect's resistance, a mass bioassay and molecular screening was performed on an autochthonous collection. Toxicity assays against neonate larvae of three lepidopteran species (Mamestra brassicae, Grapholita molesta, and Spodoptera exigua) were conducted using spore-crystal mixtures and supernatant cultures of 49 Bt isolates harboring at least one gene coding for a lepidopteran-specific insecticidal protein. A threshold of 30% of "functional mortality" was used to discriminate between "nontoxic" and "toxic" isolates. The toxicity of many Bt isolates competed with that of Btk-HD1. However, only three of them (Bl4NA, Bl5NA, and Bl9NA) showed high toxicity in both spore-crystal mixtures and supernatant cultures against the three lepidopteran species. The Bt isolates Bl4NA and Bl9NA express a protein of 130 kDa whereas the Bt isolate Bl5NA expresses a protein of 65-70 kDa. The LC-MS/MS results indicate that the major peptides in the 130 kDa band of Bl9NA were Cry1Da, Cry1Ca, Cry1Ab, and Cry1Aa, and those in the 70 kDa band of Bl5NA were Cry1Aa and Cry1Ca. The evaluation of the protein content of the supernatants by comparison to Btk-HD1 indicates the overproduction of Vip3 proteins in these strains (most likely Vip3Aa in Bl4NA and Bl9NA and Vip3Ca in Bl5NA). In addition, these three Bt strains do not produce β-exotoxins. Based on our results, the three selected strains could be considered promising candidates to be used in insect pest control.

Chitinases of Bacillus thuringiensis: Phylogeny, Modular Structure, and Applied Potentials

The most important bioinsecticide used worldwide is Bacillus thuringiensis and its hallmark is a rich variety of insecticidal Cry protein, many of which have been genetically engineered for expression in transgenic crops. Over the past 20 years, the discovery of other insecticidal proteins and metabolites synthesized by B. thuringiensis, including chitinases, antimicrobial peptides, vegetative insecticidal proteins (VIP), and siderophores, has expanded the applied value of this bacterium for use as an antibacterial, fungicidal, and nematicidal resource. These properties allow us to view B. thuringiensis not only as an entity for the production of a particular metabolite, but also as a multifaceted microbial factory. In particular, chitinases of B. thuringiensis are secreted enzymes that hydrolyze chitin, an abundant molecule in the biosphere, second only to cellulose. The observation that chitinases increase the insecticidal activity of Cry proteins has stimulated further study of these enzymes produced by B. thuringiensis. Here, we provide a review of a subset of our knowledge of B. thuringiensis chitinases as it relates to their phylogenetic relationships, regulation of expression, biotechnological potential for controlling entomopathogens, fungi, and nematodes, and their use in generating chitin-derived oligosaccharides (ChOGs) that possess antibacterial activities against a number of clinically significant bacterial pathogens. Recent advances in the structural organization of these enzymes are also discussed, as are our perspective for future studies.

In Vitro Cytotoxicity of Parasporins from Native Algerian Bacillus thuringiensis Strains Against Laryngeal and Alveolar Cancers

Parasporins (PS), a class of non-insecticidal and non-hemolytic crystal proteins of Bacillus thuringiensis (Bt), are being explored as promising anti-cancer agents due to their specific toxicity to cancer cells. This work is considered as a first initiative aiming at investigating Algerian soil Bt isolates' activity and cytotoxic potential against cancer cells. A total of 48 Bacillus spp. were isolated from different sites in Algeria. Phenotypic and biochemical tests, 16S rDNA molecular identification, and microscopic observation of crystal have confirmed the identification of Bt for ten strains. A screening for non-hemolytic crystalline proteins was performed. Extraction, purification, and activation of non-hemolytic proteins by chromatographic analysis yielded several polypeptides of different molecular weights. A purified PS1, with pro-protein of 81 kDa and several peptides with different molecular weights (18-58 kDa) after activation by trypsin, has been identified from the strain BDzG. The NH₂-terminal sequence deciphered in BLAST analysis showed homology to a Bt PS1 protein. Moreover, the screening of parasporin-1 (PS1) gene has also been performed. Cytocidal activity against human epithelial type 2 (HEp2) cells, considered to originate from a human laryngeal carcinoma, was observed with an IC₅₀ equal to 2.33 μg/ml, while moderate cytotoxicity against adenocarcinomic human alveolar basal epithelial (A549) cells has been shown with IC₅₀ equal to 18.54 μg/ml. No cytotoxicity against normal cells was noted. Fluorescence microscopy revealed a condensed or fragmented chromatin indicating the apoptotic death of HEp2 cells. Thus, Bt PS-producer isolated from Algerian soil might have a potential to join the arsenal of natural anti-cancer drugs with high therapeutic potential.

Bacterial communities of plum phyllosphere and characterization of indigenous antagonistic Bacillus thuringiensis R3/3 isolate

AIMS

The characterization of bacterial communities diversity on four local plum cultivars in two phenological stages using culture-dependent and culture-independent methods and screening among culturable plum community for indigenous bacteria active against phytopathogens.

METHODS AND RESULTS

The bacterial communities associated with leaves and fruits of four local Serbian plum cultivars (Požegača, Ranka, Čačanska Lepotica and Čačanska Rodna) were investigated in two phenological stages during early (May) and late (July) fruit maturation. Metagenomic approach revealed Methylobacterium, Sphingomonas and Hymenobacter as dominant genera. The most frequently isolated representatives with cultivable approach were pseudomonads with Pseudomonas syringae and Pseudomonas graminis, the most likely resident species of plum community. Antagonistic Bacillus thuringiensis R3/3 isolate from plum phyllosphere had ability to produce exoenzymes, reduce the growth of phytopathogenic bacteria in co-culture environment and show quorum quenching activity.

CONCLUSIONS

Plum cultivar and growth season contribute to the structure of the bacterial community associated with plum. Plum phyllosphere is good source of antagonists effective against phytopathogens.

SIGNIFICANCE AND IMPACT OF STUDY

Knowledge of bacterial communities on plum will have an impact on studies related to phyllosphere ecology and biocontrol. The indigenous antagonistic isolate, B. thuringiensis R3/3, from plum could be further investigated for its potential use in biological control of plum diseases.

The Activity of Isoquinoline Alkaloids and Extracts from Chelidonium majus against Pathogenic Bacteria and Candida sp

Chelidonium majus (Papaveraceae) extracts exhibit antimicrobial activity due to the complex alkaloid composition. The aim of the research was to evaluate the antimicrobial potential of extracts from wild plants and in vitro cultures, as well as seven major individual alkaloids. Plant material derived from different natural habitats and in vitro cultures was used for the phytochemical analysis and antimicrobial tests. The composition of alkaloids was analyzed using chromatographic techniques (HPLC with DAD detection). The results have shown that roots contained higher number and amounts of alkaloids in comparison to aerial parts. All tested plant extracts manifested antimicrobial activity, related to different chemical structures of the alkaloids. Root extract used at 31.25–62.5 mg/L strongly reduced bacterial biomass. From the seven individually tested alkaloids, chelerythrine was the most effective against P. aeruginosa (MIC at 1.9 mg/L), while sanguinarine against S. aureus (MIC at 1.9 mg/L). Strong antifungal activity was observed against C. albicans when chelerythrine, chelidonine, and aerial parts extract were used. The experiments with plant extracts, individually tested alkaloids, and variable combinations of the latter allowed for a deeper insight into the potential mechanisms affecting the activity of this group of compounds.

Characterization of Bacillus thuringiensis isolates by their insecticidal activity and their production of Cry and Vip3 proteins

Bacillus thuringiensis (Bt) constitutes the active ingredient of many successful bioinsecticides used in agriculture. In the present study, the genetic diversity and toxicity of Bt isolates was investigated by characterization of native isolates originating from soil, fig leaves and fruits from a Turkish collection. Among a total of 80 Bt isolates, 18 of them were found carrying a vip3 gene (in 23% of total), which were further selected. Insecticidal activity of spore/crystal mixtures and their supernatants showed that some of the Bt isolates had significantly more toxicity against some lepidopteran species than the HD1 reference strain. Five isolates were analyzed by LC-MS/MS to determine the Cry protein composition of their crystals. The results identified the Cry1Ac protein and a Cry2A-type protein in all isolates, Cry1Ea in 3 of them and Cry1Aa in one. The sequence analysis of the new vip3 genes showed that they had a high similarity to either vip3Aa, vip3Af or vip3Ag (94-100%). The vip3Aa gene of the 6A Bt isolate was cloned and sequenced. The protein was named Vip3Aa65 by the Bacillus thuringiensis Nomenclature Committee. The expressed and purified Vip3Aa65 protein was tested against five lepidopteran species and its toxicity compared to that of a reference protein (Vip3Aa16). Both proteins had similar toxicity against Grapholita molesta and Helicoverpa armigera, whereas Vip3Aa65 was less active than Vip3Aa16 against three species from the Spodoptera genus. A tetrameric structure of the Vip3Aa65 protein was detected by gel filtration chromatography. The study revealed some isolates with high insecticidal activity which can be considered promising candidates to be used in pest control.

Insights into the draft genome sequence of bioactives-producing Bacillus thuringiensis DNG9 isolated from Algerian soil-oil slough

Bacillus thuringiensis is widely used as a bioinsecticide due to its ability to form parasporal crystals containing proteinaceous toxins. It is a member of the Bacillus cereus sensu lato, a group with low genetic diversity but produces several promising antimicrobial compounds. B. thuringiensis DNG9, isolated from an oil-contaminated slough in Algeria, has strong antibacterial, antifungal and biosurfactant properties. Here, we report the 6.06 Mbp draft genome sequence of B. thuringiensis DNG9. The genome encodes several gene inventories for the biosynthesis of bioactive compounds such as zwittermycin A, petrobactin, insecticidal toxins, polyhydroxyalkanoates and multiple bacteriocins. We expect the genome information of strain DNG9 will provide another model system to study pathogenicity against insect pests, plant diseases, and antimicrobial compound mining and comparative phylogenesis among the Bacillus cereus sensu lato group.

Diversity of Bacillus thuringiensis Strains From Qatar as Shown by Crystal Morphology, δ-Endotoxins and Cry Gene Content

Bacillus thuringiensis (Bt) based insecticidal formulations have been recognized as one of the most successful, environmentally safe and sustainable method of controlling insect pests. Research teams worldwide are in search of Bt diversity giving more choices of bio-insecticides and alternatives to address insect resistance. In fact, there are many unexplored ecologies that could harbor novel Bt strains. This study is the first initiative to explore Bt strain diversity in Qatar. A collection of 700 Bt isolates was constructed. Scanning electron microscopy of Bt crystals showed different crystal forms, with a high abundance of spherical crystals compared to the bipyramidal ones. Among the spherical crystals, four different morphologies were observed. The δ-endotoxin content of parasporal crystals from each Bt isolate revealed that there are 16 different protein profiles among the isolates of the collection. On the other hand, plasmid pattern analysis showed seven different plasmid profiles. Their insecticidal activity was predicted by exploring the δ-endotoxin coding genes and conducting qualitative insecticidal bioassays. 19 smooth spherical crystal producing isolates have been identified that could be possible candidates for endotoxin production targeting Dipteran insects. Another group of 259 isolates producing bipyramidal and cuboidal crystals could target Lepidopteran and Coleopteran insects. The remaining 422 isolates have novel profiles. In conclusion, Qatari soil ecology provides a good collection and diversity of Bt isolates. In addition to strains harboring genes encoding common endotoxins, the majority are different and very promising for the search of novel insecticidal endotoxins.

Molecular characterization of the gene profile of Bacillus thuringiensis Berliner isolated from Brazilian ecosystems and showing pathogenic activity against mosquito larvae of medical importance

The occurrence of Aedes aegypti, Culex quinquefasciatus, and mosquitoes of the genus Anopheles potentiate the spread of several diseases, such as dengue, Zika, chikungunya, urban yellow fever, filariasis, and malaria, a situation currently existing in Brazil and in Latin America. Control of the disease vectors is the most effective tool for containing the transmission of the pathogens causing these diseases, and the bacterium Bacillus thuringiensis var. israelensis has been widely used and has shown efficacy over many years. However, new B. thuringiensis (Bt) strains with different gene combinations should be sought for use as an alternative to Bti and to prevent the resistant insects selected. Aiming to identify diversity in the Bt in different Brazilian ecosystems and to assess the pathogenicity of this bacterium to larvae of Ae. aegypti, C. quinquefasciatus, and Anopheles darlingi, Bt strains were obtained from the Amazon, Caatinga (semi-arid region), and Cerrado (Brazilian savanna) biomes and tested in pathogenicity bioassays in third-instar larvae of Ae. aegypti under controlled conditions in the laboratory. The isolates with larvicidal activity to larvae of Ae. aegypti were used in bioassays with the larvae of C. quinquefasciatus and An. darlingi and characterized according to the presence of 14 cry genes (cry1, cry2, cry4, cry10, cry11, cry24, cry32, cry44Aa, cry1Ab, cry4Aa, cry4Ba, cry10Aa, cry11Aa, and cry11Ba), six cyt genes (cyt1, cyt2, cyt1Aa, cyt1Ab, cyt2Aa and cyt2Ba), and the chi gene. Four hundred strains of Bt were isolated: 244 from insects, 85 from Amazon soil, and 71 from the Caatinga biome. These strains, in addition to the 153 strains isolated from Cerrado soil and obtained from the Entomopathogenic Bacillus Bank of Maranhão, were tested in bioassays with Ae. aegypti larvae. A total of 37 (6.7%) strains showed larvicidal activity, with positive amplification of the cry, cyt, and chi genes. The most frequently amplified genes were cry4Aa and cry4Ba, both occurring in 59.4% in these strains, followed by cyt1Aa and cyt2Aa, with 56.7% and 48% occurrence, respectively. Twelve (2.2%) strains that presented 100% mortality within 24h were used in bioassays to estimate the median lethal concentration (LC₅₀) for Ae. aegypti larvae. Two strains (BtMA-690 and BtMA-1114) showed toxicity equal to that of the Bti standard strain, and the same LC₅₀ value (0.003mg/L) was recorded for the three bacteria after 48h of exposure. Detection of the presence of the Bt strains that showed pathogenicity for mosquito larvae in the three biomes studied was possible. Therefore, these strains are promising for the control of insect vectors, particularly the BtMA-1114 strain, which presents a gene profile different from that of Bti but with the same toxic effect.