Toxic Strains Research Articles

The potential mosquitocidal activity of cry4A toxic region crystal protein gene from local isolates of Bacillus thuringiensis against Aedes aegypti

The present study was conducted to isolate Bacillus thuringiensis (B.t.) strains from different ecological regions of Pakistan and determined the mosquitocidal activity of cry4A crystal protein gene against the dipteran insects. Out of 25 B.t. isolates, 5 isolates were selected on the basis of toxicity and 4 were identified as Bacillus thuringiensis GCU-DAB-TK-04 (MN922746), GCU-DAB-TK-06 (MT032397), GCU-DAB-TK-09 (MN922747), and GCU-DAB-TK-13 (MT032398). GCU-DAB-TK-04 was found to be the most toxic strain against the 3rd instar larvae of Aedes aegypti. The presence of Cry 4A protein was confirmed by the amplification of cry4A gene (accession number MT001910) from GCU-DAB-TK-04. The highest spores toxicity was shown by GCU-DAB-TK-04 (LC50 = 104 μg/ml) while LC50 values of other strains were GCU-DAB-TK-13 (LC50 = 602 ± 0.43 μg/ml) GCU-DAB-TK-06 (LC50 = 812 ± 0.63 μg/ml), GCU-DAB-TK-12 (LC50 = 1230 ± 1.14 μg/ml), and GCU-DAB-TK-09 (LC50 = 7585 ± 1.17 μg/ml). Similarly, the highest toxicity of total cell protein was also shown by GCU-DAB-TK-04 (LC50=676 ± 0.53 μg/ml while LC50 values of other strains were GCU-DAB-TK-13 (LC50 = 724 ± 1.12 μg/ml), GCU-DAB-TK-06 (LC50 = 741 ± 0.64 μg/ml), GCU-DAB-TK-12 (LC50 = 912 ± 0.65 μg/ml), and GCU-DAB-TK-09 (LC50 = 1621 ± 1.13 μg/ml). The order of toxicity of B.t. strains was GCU-DAB-TK-04 > GCU-DAB-TK-13 > GCU-DAB-TK-06 > GCU-DAB-TK-12 > GCU-DAB-TK-09. Protein analysis showed that 130 kDa (probably Cry4A, B), 70 kDa (Cry4C, D) and 20 kDa (Cyt enhancer protein of Cry4) proteins were present in all B.t. strains. These B.t. strains have found great potential to grow into bio-insecticidal formulation for the eco-friendly control of mosquitoes.

Selection and Development of Nontoxic Nonproteolytic Clostridium botulinum Surrogate Strains for Food Challenge Testing.

Clostridium botulinum causes severe foodborne intoxications by producing a potent neurotoxin. Challenge studies with this pathogen are an important tool to ensure the safety of new processing techniques and newly designed or modified foods, but they are hazardous and complicated by the lack of an effective selective counting medium. Therefore, this study aimed to develop selectable nontoxic surrogate strains for group II, or nonproteolytic, C. botulinum, which are psychotropic and hence of particular concern in mildly treated, refrigerated foods. Thirty-one natural nontoxic nonproteolytic strains, 16 of which were isolated in this work, were characterized in detail, revealing that 28 strains were genomically and phenotypically indistinguishable from toxic strains. Five strains, representing the genomic and phenotypic diversity of group II C. botulinum, were selected and successfully equipped with an erythromycin (Em) resistance marker in a defective structural phage gene without altering phenotypic features. Finally, a selective medium containing Em, cycloserine (Cs), gentamicin (Gm), and lysozyme (Ly) was developed, which inhibited the background microbiota of commercial cooked ham, chicken filet, and salami, but supported spore germination and growth of the Em-resistant surrogate strains. The surrogates developed in this work are expected to facilitate food challenge studies with nonproteolytic C. botulinum for the food industry and can also provide a safe alternative for basic C. botulinum research.

Overcoming Poor Transgene Expression in the Wild-Type Chlamydomonas Chloroplast: Creation of Highly Mosquitocidal Strains of Chlamydomonas reinhardtii.

High-level expression of transgenes in the chloroplast of wild-type Chlamydomonas reinhardtii (C. reinhardtii) remains challenging for many genes (e.g., the cry toxin genes from Bacillus thuringiensis israelensis). The bottleneck is presumed to be post-transcriptional and mediated by the 5′ element and the coding region. Using 5′ elements from highly expressed photosynthesis genes such as atpA did not improve the outcome with cry11A regardless of the promoter. However, when we employed the 5′ UTR from mature rps4 mRNA with clean fusions to promoters, production of the rCry11A protein became largely promoter-dependent. The best results were obtained with the native 16S rrn promoter (−91 to −1). When it was fused to the mature 5′ rps4 UTR, rCry11A protein levels were ~50% higher than was obtained with the inducible system, or ~0.6% of total protein. This level was sufficient to visualize the 73-kDa rCry11A protein on Coomassie-stained gels of total algal protein. In addition, analysis of the expression of these transgenes by RT-PCR indicated that RNA levels roughly correlated with protein production. Live cell bioassays using the best strains as food for 3rd instar Aedes aegypti larvae showed that most larvae were killed even when the cell concentration was as low as 2 × 104 cells/mL. Finally, the results indicate that these highly toxic strains are also quite stable, and thus represent a key milestone in using C. reinhardtii for mosquito control.

Role of a conserved family of serine hydrolases in ethanol toxicity

A recent CRISPR screen for genes involved in controlling acetaldehyde dependent ethanol toxicity, identified OVCA2, a conserved serine hydrolase, as the highest protectant against acetaldehyde toxicity. OVCA2 is a member of a larger, diverse group of proteins responsible for metabolic activities known as the family of serine hydrolases (FSH). In S. cerevisiae,three FSH homologues (FSH1, FSH2, and FSH3) are present, but their overlapping functions and their connection to acetaldehyde toxicity are unknown. In this study, we worked to understand the role of FSH proteins in controlling acetaldehyde toxicity in two divergent ways. First, we compared the substrate specificity of the three FSH homologues from S. cerevisiae against a library of ester substrates at varying pH environments. Second, we constructed combinatorial deletions of FSH genes in S. cerevisiae and screened deletion strains for changes in growth under high ethanol, acetaldehyde, and varying other toxic aldehydes. For enzyme activity, both FSH2 and FSH3 had a preference for alkaline conditions and thus the comparative substrate specificity screen was completed at pH 7.5. In this screen, FSH2 and FSH3 showed substrate preferences in line with FSH1, as they both preferred short chain esters versus longer chain esters (>8C). To further evaluate the metabolic activity of FSH enzymes in acetaldehyde toxicity, single, double, and triple deletion strains of the three FSH genes were made in S. cerevisiae. Proper gene deletions for each strain were confirmed by colony PCR. Each of the deletion strains were then grown on agar plates with varying concentrations of alcohol and aldehyde toxins. Each of the single deletion mutants showed similar growth rates to each other and to the wild‐type strain by spot dilution but exhibited slightly different colony morphology from the wild‐type strain. Further testing on the ability to withstand toxins produced by the alcohol metabolism pathway will be conducted to determine whether these enzymes and OVCA2 can metabolize the toxic byproducts of ethanol production.

Co-occurrence of Alexandrium minutum (Dinophyceae) ribotypes from the Chinese and Malaysian coastal waters and their toxin production

The bloom-forming dinophyte Alexandrium minutum comprises biogeographic inferred, global and Pacific clades with both toxic and nontoxic strains reported. A. minutum has a wide distribution in the Western Pacific, but to date only a few strains have available DNA sequences. To fully understand its genetic diversity, sampling was undertaken from the Yellow Sea, the East and South China Sea, and five strains of A. minutum and two strains of its sister species, A. tamutum, were established. Their morphology was examined by light and scanning electron microscopy. In addition, sequences were obtained from both large subunit (LSU) ribosomal DNA and/or internal transcribed spacer (ITS) region. Strains of A. minutum are morphologically indistinguishable, characterized by a smaller cell size and a narrow sixth precingular plate. In contrast, A. tamutum has a wider sixth precingular plate. High nucleotide divergences of LSU (D1–D3) rDNA and ITS were revealed amongst strains of A. minutum (10% and 25%, respectively), and A. tamutum (3% and 13%, respectively). Molecular phylogenies based on LSU rDNA and ITS revealed three ribotypes (B–D) of A. minutum, and two ribotypes of A. tamutum in the Western Pacific. Seasonal sampling in the East China Sea to detect A. minutum using the DNA metabarcoding targeting ITS1 region was also performed. Our results showed that the ribotypes B and C of A. minutum co-occurred in the water. Paralytic shellfish toxin (PSTs) of all seven strains was analysed using liquid chromatography with tandem mass spectrometry (LC–MS/MS). PSTs were detected only in A. minutum ribotypes B and C with predominance of gonyautoxins 1/4. Our results suggest high diversity and risk potential of this toxic species in this region.

A new strain of Neowestiellopsis (Hapalosiphonaceae): first observation of toxic soil cyanobacteria from agricultural fields in Iran

BackgroundIn the present research, challenges arose when many reports have been published on the poisoning of humans due to the ingestion of crops of Crataegus plants contaminated with cyanobacterial toxins. The discovery of several poisonings around agricultural zones prompted us to study the toxic compounds in a strain of Neowestiellopsis which is the most abundant in the agricultural zones of Kermanshah province of Iran, using a polyphasic approach. Molecular procedure was followed to study these strains deeply.Material and methodsTo elucidate their systematic position, besides the 16S rRNA gene, the analyses of molecular toxicity markers, namely nos, mcy G, mcy D and internal transcribed spacer (ITS), were also used.ResultsBased on the results, for the first time, we record the presence of a gene cluster coding for the biosynthesis of a bioactive compound (Nostopeptolides) that is very rare in this family and the presence of toxic compounds (microcystin), which might account for the poisoning of humans.ConclusionsThis case is the first observation of a toxic soil strain from the genus Neowestiellopsis from agricultural fields in Iran.

Cyanobacterium Raphidiopsis raciborskii and its toxin in Buon Phong reservoir, Dak Lak province, Vietnam

This study investigated the variation of the cyanobacterium Raphidiopsis raciborskii population under the influence of physicochemical parameters from May 2019 to April 2020 in the Buon Phong reservoir. The correlations between these parameters were explored by using Principal Component Analysis (PCA) and Pearson correlation analysis. The cylindrospermopsin (CYN) toxin in isolated strains from the reservoir was confirmed by using High-performance liquid chromatography (HPLC) analyses. R. raciborskii presented throughout the year in the reservoir with a biovolume from 0.12 to 9.14 mm3 L-1. Four R. raciborskii strains (CBP2, CBP3, CBP4, and CBP5) were successfully isolated and confirmed to produce CYN by the HPLC results. The highest concentration in isolated strains was 0.345 μg g-1 DW in the CBP4 strain. The PCR results of genes responsible for CYN biosynthesis showed that the PCR amplicons of cyrB and CyrC were amplified in two toxic strains (CBP2 and CBP3), while the amplicons of both cyrB and cyrC were not observed in two remaining toxic strains. In addition, such abiotic factors as temperature and nutrients played major roles in the abundance of R. raciborskii. Moreover, the biovolume of R. raciborskii positively correlated with the CYN concentrations in the Buon Phong reservoir.

Comprehensive and functional analyses reveal the genomic diversity and potential toxicity of Microcystis

Microcystis is a cyanobacteria that is widely distributed across the world. It has attracted great attention because it produces the hepatotoxin microcystin (MC) that can inhibit eukaryotic protein phosphatases and pose a great risk to animal and human health. Due to the high diversity of morphospecies and genomes, it is still difficult to classify Microcystis species. In this study, we investigated the pangenome of 23 Microcystis strains to detect the genetic diversity and evolutionary dynamics. Microcystis revealed an open pangenome containing 22,009 gene families and exhibited different functional constraints. The core-genome phylogenetic analysis accurately differentiated the toxic and nontoxic strains and could be used as a taxonomic standard at the genetic level. We also investigated the functions of HGT events, of which were mostly conferred from cyanobacteria and closely related species. In order to detect the potential toxicity of Microcystis, we searched and characterized MC biosynthetic gene clusters and other secondary metabolite gene clusters. Our work provides insights into the genetic diversity, evolutionary dynamics, and potential toxicity of Microcystis, which could benefit the species classification and development of new methods for drinking water quality control and management of bloom formation in the future.

Potential of Accelerometers and GPS Tracking to Remotely Detect Perennial Ryegrass Staggers in Sheep

Perennial ryegrass staggers (staggers) is a neurotoxic condition in livestock that is caused by consumption of ryegrass (Lolium perenne) infected with specific strains of Epichloë fungal endophytes. These grass-endophyte associations produce toxins that can adversely affect animals and can in some cases lead to death. In sheep, symptoms typically include head shaking, changes in gait, stiffness and falling. Affected sheep can recover after removing them from pastures containing toxic strains of endophyte. A pilot case study was conducted in Lincoln, New Zealand to determine if ryegrass staggers could be identified with data collected through GPS tracking and accelerometers. Fourteen sheep per treatment grazed in either a toxic endophyte-infected ryegrass paddock or an endophyte-free control paddock for 17 days in late March and early April 2017. Randomly selected sheep were fitted with collars containing a 3-axis accelerometer recording movements at 12 Hz (10 collars in endophyte infected paddock and 6 in the control paddock). Three sheep per treatment were also tracked at 3-minute intervals with GPS receivers. Sheep were scored by an experienced observer for symptoms of staggers weekly and at the end of the study using a 0 to 5 scale. Control sheep did not display any symptoms of staggers and 10 sheep in the infected pasture displayed little or no symptoms (0 or 1 score). The other 4 sheep in infected pasture had scores from 2 to 4 at the end of the study. Sheep grazing in the infected pasture (2.91 m/min ± 0.04 SE) moved slower (P=0.04) than sheep in the control pasture (3.12 m/min ± 0.05 SE). Distance travelled varied among days, but there did not appear to be any temporal trends. Machine learning analyses of accelerometer data showed that the behavior of affected sheep changed during the study. Activity of sheep displaying symptoms (scores ≥ 2) increased more in the morning and midday during the latter part of the study than control sheep and sheep with few or no symptoms (score < 2). However, behavior of individual sheep at night remained relatively consistent during the study. Accelerometers may be useful for remotely detecting perennial ryegrass staggers.

Islet amyloid polypeptide cross-seeds tau and drives the neurofibrillary pathology in Alzheimer\u2019s disease

BackgroundThe pathologic accumulation and aggregation of tau is a hallmark of tauopathies including Alzheimer’s disease (AD). However, the molecular mechanisms mediating tau aggregation in AD remain elusive. The incidence of AD is increased in patients with type 2 diabetes (T2DM), which is characterized by the amyloid deposition of islet amyloid polypeptide (IAPP) in the pancreas. However, the molecular mechanisms bridging AD and T2DM remain unknown.MethodsWe first examined the presence of IAPP in the neurofibrillary tangles of AD patients. Then we tested the effect of IAPP on tau aggregation. The biochemical and biological characteristics of the IAPP-tau fibrils were tested in vitro. The seeding activity and neurotoxicity of the IAPP-tau fibrils were confirmed in cultured neurons. Lastly, the effect of IAPP on tau pathology and cognitive impairments was determined by injecting the IAPP-tau fibrils and IAPP fibrils into the hippocampus of tau P301S mice.ResultsWe found that IAPP interacts with tau and accelerates the formation of a more toxic strain, which shows distinct morphology with enhanced seeding activity and neurotoxicity in vitro. Intrahippocampal injection of the IAPP-tau strain into the tau P301S transgenic mice substantially promoted the spreading of tau pathology and induced more severe synapse loss and cognitive deficits, when compared with tau fibrils. Furthermore, intracerebral injection of synthetic IAPP fibrils initiated tauopathy in the brain of tau P301S transgenic mice.ConclusionsThese observations indicate that IAPP acts as a crucial mediator of tau pathology in AD, and provide a mechanistic explanation for the higher risk of AD in individuals with T2DM.

Toxicity of the Diatom Genus Pseudo-nitzschia (Bacillariophyceae): Insights from Toxicity Tests and Genetic Screening in the Northern Adriatic Sea.

Diatoms of the genus Pseudo-nitzschia H.Peragallo are known to produce domoic acid (DA), a toxin involved in amnesic shellfish poisoning (ASP). Strains of the same species are often classified as both toxic and nontoxic, and it is largely unknown whether this difference is also genetic. In the Northern Adriatic Sea, there are virtually no cases of ASP, but DA occasionally occurs in shellfish samples. So far, three species—P. delicatissima (Cleve) Heiden, P. multistriata (H. Takano) H. Takano, and P. calliantha Lundholm, Moestrup, & Hasle—have been identified as producers of DA in the Adriatic Sea. By means of enzme-linked immunosorbent assay (ELISA), high-performance liquid chromatography with UV and visible spectrum detection (HPLC-UV/VIS), and liquid chromatography with tandem mass spectrometry (LC-MS/MS), we reconfirmed the presence of DA in P. multistriata and P. delicatissima and detect for the first time in the Adriatic Sea DA in P. galaxiae Lundholm, & Moestrup. Furthermore, we attempted to answer the question of the distribution of DA production among Pseudo-nitzschia species and strains by sequencing the internal transcribed spacer (ITS) phylogenetic marker and the dabA DA biosynthesis gene and coupling this with toxicity data. Results show that all subclades of the Pseudo-nitzschia genus contain toxic species and that toxicity appears to be strain dependent, often with geographic partitioning. Amplification of dabA was successful only in toxic strains of P. multistriata and the presence of the genetic architecture for DA production in non-toxic strains was thus not confirmed.

Effects of Varying Temperature on the Growth Rate of Toxic and Non-Toxic Strains of &amp;lt;i&amp;gt;Microcystis aeruginosa&amp;lt;/i&amp;gt;

Cyanobacterial bloom, also called blue-green algae, all over the world is generating great concern due to the effect of temperature resulting from global warming. Microcystis aeruginosa is well known to be the major causative agent of algal bloom. However, there is a need for more critical detection to the relationship between temperature and the growth rate of Microcystic aeruginosa. In the present study, we cultivated the batch culture of Microcystis aeruginosa (Toxic and Non-toxic strain) at five different temperatures 5°C, 10°C, 22°C, 27°C, and 38°C to measure its specific growth rate, pigment contents and cell concentration at each temperature. Our findings indicate that non-toxic strains had higher growth rate at high temperature than the toxic strains, particularly at 22°C. Also, a minimal difference was noticed with the chlorophyll a, carotenoid contents of both strains at varying temperature. The above results indicate the significance of temperature in respect to the two strains of M. aeruginosa and could constitute a promising tool in the prediction of algal bloom.

Triagem de genes produtores de cianotoxinas em sistemas de água doce do Equador

Abstract: Aim This study pursued the detection of cyr and mcy genes to assess the presence of cylindrospemopsin (CN) and microcystin (MC) potential producers in Ecuadorian water bodies. Methods Environmental DNA (eDNA) was extracted from eight water bodies and one wastewater treatment plant (WWTP) from Ecuador. A nested PCR was designed to amplify mcyB, cyrE, and cyrJ genes in these environmental samples. PCR products were sequenced and blasted against GenBank database. Results Potential CN producers were found in seven water bodies and the WWTP. cyrE amplification revealed three variants belonging to Raphidopsis and Aphanizmenon species and one for cyrJ with around 90% identity with Raphidiopsis and Oscillatoria species. Four water bodies presented the same variant for mcyB similar to Microcystis panniformis with 99% of identity. Conclusions This study contributes new data on the presence of toxic cyanobacteria strains and provides new molecular tools to assess cyanotoxin hazards in Ecuadorian water bodies.

Non-targeted metabolomic profiling of filamentous cyanobacteria Aphanizomenon flos-aquae exposed to a concentrated culture filtrate of Microcystis aeruginosa

Microcystis and Aphanizomenon are two toxic cyanobacteria genera, which frequently cause blooms in freshwater lakes. In some cases, succession of these two genera was observed in natural water bodies. Among the diverse factors contributing to such succession of dominant cyanobacterial genera, an allelopathic effect was proposed to be involved after the growth inhibitory effect of several Microcystis species on A. flos-aquae was investigated. However, the response of target species exposed to Microcystis are poorly described. In the present study, we used two toxic cyanobacteria strains, Aphanizomenon flos-aquae (Aph1395) and Microcystis aeruginosa strain 905 (Ma905) as research subjects. Aph1395 was inhibited with a necessarily concentrated culture filtrate of Ma905 (MA905-SPE), and the response of the inhibited Aph1395 cells was explored via non-targeted metabolomic profiling. In total, 3735 features were significantly different in the Aph1395 treated with Ma905-SPE vs. those treated with BG11 medium. Among them, the annotations of 146 differential features were considered to be confident via MS/MS spectrum matching analysis. Based on the reported physiological functions of the annotated differential features, we proposed a putative model that in the growth-inhibited Aph1395, a suite of increased or decreased features with activities in apoptosis, growth inhibition, and stress response processes contributed to, or defended against, the allelopathic effect caused by Ma905. Our findings provide insights into the interaction between the bloom forming cyanobacterial species that share the same ecological environment.

Latitudinal Variation in the Toxicity and Sexual Compatibility of Alexandrium catenella Strains from Southern Chile.

The bloom-forming toxic dinoflagellate Alexandrium catenella was first detected in southern Chile (39.5–55° S) 50 years ago and is responsible for most of the area’s cases of paralytic shellfish poisoning (PSP). Given the complex life history of A. catenella, which includes benthic sexual cysts, in this study, we examined the potential link between latitude, toxicity, and sexual compatibility. Nine clones isolated from Chilean Patagonia were used in self- and out-crosses in all possible combinations (n = 45). The effect of latitude on toxicity, reproductive success indexes, and cyst production was also determined. Using the toxin profiles for all strains, consisting of C1, C2, GTX4, GTX1, GTX3, and NeoSTX, a latitudinal gradient was determined for their proportions (%) and content per cell (pg cell−1), with the more toxic strains occurring in the north (−40.6° S). Reproductive success also showed a latitudinal tendency and was lower in the north. None of the self-crosses yielded resting cysts. Rather, the production of resting cysts was highest in pairings of clones separated by distances of 1000–1650 km. Our results contribute to a better understanding of PSP outbreaks in the region and demonstrate the importance of resting cysts in fueling new toxic events. They also provide additional evidence that the introduction of strains from neighboring regions is a cause for concern.

Bioenergy as a prospective energy source in the future

The issues of global warming and greenhouse gasses have raised the concern of the people and led to integrate ambitious of using bioenergy in many countries. In this paper, the issues of conventional energy are stated, and the different types of conventional energy resources are discussed including coal, petroleum and natural gas. The process of pulverized coal combustion (PCC) to generate electricity is also studied and discussed in this paper to have a better understanding of the process and the emission of greenhouse gas released from the use of coal to generate conventional energy. The reason of soil contamination and air pollution caused by the refinery process of petroleum is also discussed in this paper and several study cases of the social economic impact caused by the production of natural gas in development countries. Furthermore, the used of bioenergy and different type of bioenergy resource are discussed including biogas, algae biofuel, and biodiesel. The process of algae cultivation for algae biofuel and the study of toxic waste algae strains that can give a negative impact to the environment is studied to avoid harmful substances released to the environment. The potential algae application in different fields is also included to show the benefit of algae biofuel which is flexible and able to contribute to the global economic growth. Lastly, the advantages of using bioenergy are discussed including the mitigation of greenhouse gas emission, improve social economic growth, renewable energy resources and prevent prescribed burning of the forest.

Groundwater and society: fresh submarine groundwater discharge and itsmanagement improvement

The issues of global warming and greenhouse gasses have raised the concern of the people and led to integrate ambitious of using bioenergy in many countries. In this paper, the issues of conventional energy are stated, and the different types of conventional energy resources are discussed including coal, petroleum and natural gas. The process of pulverized coal combustion (PCC) to generate electricity is also studied and discussed in this paper to have a better understanding of the process and the emission of greenhouse gas released from the use of coal to generate conventional energy. The reason of soil contamination and air pollution caused by the refinery process of petroleum is also discussed in this paper and several study cases of the social economic impact caused by the production of natural gas in development countries. Furthermore, the used of bioenergy and different type of bioenergy resource are discussed including biogas, algae biofuel, and biodiesel. The process of algae cultivation for algae biofuel and the study of toxic waste algae strains that can give a negative impact to the environment is studied to avoid harmful substances released to the environment. The potential algae application in different fields is also included to show the benefit of algae biofuel which is flexible and able to contribute to the global economic growth. Lastly, the advantages of using bioenergy are discussed including the mitigation of greenhouse gas emission, improve social economic growth, renewable energy resources and prevent prescribed burning of the forest.

Nutrient Regulation of Relative Dominance of Cylindrospermopsin-Producing and Non-cylindrospermopsin-Producing Raphidiopsis raciborskii.

Raphidiopsis raciborskii (previously Cylindrospermopsis raciborskii) can produce cylindrospermopsin (CYN) which is of great concern due to its considerable toxicity to human and animals. Its CYN-producing (toxic) and non-CYN-producing (non-toxic) strains co-exist commonly in natural water bodies, while how their relative dominance is regulated has not been addressed. In this study, we combined field investigation with laboratory experiments to assessed the relationship between toxic and non-toxic R. raciborskii abundances under different nutrient levels. The rpoC1- and cyrJ-based qPCR was applied for quantifying total and toxic R. raciborskii abundances, respectively. The field survey showed that toxic R. raciborskii was detected in 97 of 115 reservoirs where its proportion ranged from 0.3% to 39.7% within the R. raciborskii population. Both total and toxic R. raciborskii abundances increased significantly with trophic level of these reservoirs, consistent with our monoculture and co-culture experiments showing in an increase in R. raciborskii growth with increasing nitrogen (N) or phosphorus (P) concentrations. In the monoculture experiments, growth rates of non-toxic and toxic strains from Australia or China were not significantly different under the same culture conditions. On the other hand, in the co-culture experiments, the toxic strains displayed a significantly faster growth than non-toxic strains under nutrient-replete conditions, resulting in an obvious shift toward the dominance by toxic strains from day 3 to the end of the experiments, regardless of the strain originating from Australia or China. The reverse was found under N- or P-limited conditions. Our results indicated that the toxic strains of R. raciborskii have a competitive advantage relative to the non-toxic strains in a more eutrophic world. In parallel to an increase in dominance, both toxic strains grown in the mixed population significantly increased CYN production under nutrient-replete conditions as compared to nutrient-limited conditions, suggesting that CYN may be of significance for ecological advantage of toxic R. raciborskii. These results highlight the importance of nutrient availability in regulating abundances and strain dominance of two genotypes of R. raciborskii. Our findings demonstrated that elevated nutrients would favor the growth of CYN-producing R. raciborskii and CYN production, leading to more blooms with higher toxicity at global scale.

Combination impacts of gamma radiation and low temperature on the toxin‐producingBacillus cereusisolated from fried and steam rice

Thirty randomly collected steam and fried rice sample from Dhaka City were investigated for toxin-producing Bacillus cereus to observe the antibiotic sensitivity and survival ability of the toxic strain in combination treatment of gamma radiation and low temperature. Twenty-nine strains of Bacillus spp. were isolated and seven strains were confirmed as pathogenic B. cereus. A known toxic strain KTCC 11,204 and seven pathogenic strains were subjected to cytotoxic effect analysis using Vero cell through protein estimation. KTCC 11,204 and one toxic B. cereus strain was treated by gamma radiation at 4, 6 and 8 kGy dose and 4°C temperature for three consecutive days. At third day of storage, Toxic B. cereus count was significantly low and totally eliminated at 8 kGy dose during all storage period. The toxic B. cereus was further tested against 10 antibiotics and found highly sensitive to imipenem, penicillin, amoxycillin, ampicillin, and chloramphenicol. Novelty Impact statement Toxin-producing Bacillus spp. were isolated from steam and fried rice sample. The toxic B. cereus was found highly sensitive to imipenem, penicillin, amoxycillin, ampicillin, and chloramphenicol. Different doses of gamma ray and 4°C temperature result in a significant reduction of toxic B. cereus count.

Genome Streamlining, Plasticity, and Metabolic Versatility Distinguish Co-occurring Toxic and Nontoxic Cyanobacterial Strains of Microcoleus.

ABSTRACTHarmful cyanobacterial bloom occurrences have increased worldwide due to climate change and eutrophication, causing nuisance and animal deaths. Species from the benthic cyanobacterial genus Microcoleus are ubiquitous and form thick mats in freshwater systems, such as rivers, that are sometimes toxic due to the production of potent neurotoxins (anatoxins). Anatoxin-producing (toxic) strains typically coexist with non-anatoxin-producing (nontoxic) strains in mats, although the reason for this is unclear. To determine the genetic mechanisms differentiating toxic and nontoxic Microcoleus, we sequenced and assembled genomes from 11 cultures and compared these to another 31 Microcoleus genomes. Average nucleotide identities (ANI) indicate that toxic and nontoxic strains are distinct species (ANI, <95%), and only 6% of genes are shared across all 42 genomes, suggesting a high level of genetic divergence among Microcoleus strains. Comparative genomics showed substantial genome streamlining in toxic strains and a potential dependency on external sources for thiamine and sucrose. Toxic and nontoxic strains are further differentiated by an additional set of putative nitrate transporter (nitrogen uptake) and cyanophycin (carbon and nitrogen storage) genes, respectively. These genes likely confer distinct competitive advantages based on nutrient availability and suggest nontoxic strains are more robust to nutrient fluctuations. Nontoxic strains also possess twice as many transposable elements, potentially facilitating greater genetic adaptation to environmental changes. Our results offer insights into the divergent evolution of Microcoleus strains and the potential for cooperative and competitive interactions that contribute to the co-occurrence of toxic and nontoxic species within mats.