Combined effects of bacterial-feeding nematodes and prometryne on the soil microbial activity

Variation of microbial activities and communities in petroleum-contaminated soils induced by the addition of organic materials and bacterivorous nematodes

Bacterivorous nematodes are abundant in petroleum-contaminated soils. However, the ecological functions of bacterivorous nematodes and their impacts together with the addition of organic materials on the activity and diversity of microorganisms in petroleum-contaminated soils remain unknown. To assess such effects, six treatments were established in this study, including uncontaminated nematodes-free soil (Control), petroleum-contaminated soil (PC), petroleum-contaminated soil + 5 nematodes per gram dry soil (PCN), and petroleum-contaminated soil + 5 nematodes per gram dry soil + 1% wheat straw (PCNW), or + 1% rapeseed cake (PCNR), or + 1% biochar (PCNB). Results showed that the enzyme activities in the six treatments generally increased firstly and then decreased during the incubation period. Compared with Control, the invertase activity in PCNW, PCNR, and PCNB increased by 80.6%, 313.5%, and 12.4%, respectively, whereas the urease activity in PC, PCN, PCNW, PCNR, and PCNW increased by 1.2%, 25.5%, 124.3%, 105.3%, and 25.5%, respectively. Petroleum pollution, inoculation of bacterivorous nematodes, and the addition of organic materials all significantly boosted the concentrations of phospholipid fatty acids (PLFAs) of soil bacteria, actinobacteria, and total microorganisms, and increased the concentrations of both G⁺ and G^- bacteria PLFAs and the ratio of G^-/G⁺. The concentration of fungi PLFAs and the ratio of fungi to bacteria were significantly higher in PCNW and PCNR than those in other treatments. Overall, adding bacterivorous nematodes and organic materials to the petroleum-contaminated soil significantly improved soil microbial activity and community structure, suggesting that bacterivorous nematodes could be used for the bioremediation in petroleum contaminated soils.

Ultrasensitive electrochemiluminescence sensor based on perovskite quantum dots coated with molecularly imprinted polymer for prometryn determination

A highly effective molecularly imprinted electrochemiluminescence sensor was constructed for prometryn determination in environmental and biological samples by using perovskite quantum dots coated with a molecularly imprinted silica layer (MIP/CsPbBr₃-QDs) as the recognition and response element. MIP/CsPbBr₃-QDs were immobilized on a glassy carbon electrode (GCE) through electropolymerization, and the electrochemiluminescence (ECL) response of MIP/CsPbBr₃-QDs could be motivated under the condition of H₂O₂ as co-reactant. ECL signal was selectively quenched with prometryn by hindering electron transfer and directly proportional to the logarithm of prometryn concentration (0.10-500.0 μg/L) with a correlation coefficient of 0.9960. Limits of detection in fish and seawater samples were 0.010 μg/kg and 0.050 μg/L, respectively. Excellent recoveries of 88.0%-106.0% were acquired for fish and seawater samples with a relative standard deviation below 4.2%. The constructed MIECL sensor based on MIP/CsPbBr₃-QDs showed good stability, accuracy, and precision for sensitive detection of prometryn in aquaculture products and environmental samples.

Complete Genome Sequence and Function Gene Identify of Prometryne-Degrading Strain Pseudomonas sp. DY-1

The genus Pseudomonas is widely recognized for its potential for environmental remediation and plant growth promotion. Pseudomonas sp. DY-1 was isolated from the agricultural soil contaminated five years by prometryne, it manifested an outstanding prometryne degradation efficiency and an untapped potential for plant resistance improvement. Thus, it is meaningful to comprehend the genetic background for strain DY-1. The whole genome sequence of this strain revealed a series of environment adaptive and plant beneficial genes which involved in environmental stress response, heavy metal or metalloid resistance, nitrate dissimilatory reduction, riboflavin synthesis, and iron acquisition. Detailed analyses presented the potential of strain DY-1 for degrading various organic compounds via a homogenized pathway or the protocatechuate and catechol branches of the β-ketoadipate pathway. In addition, heterologous expression, and high efficiency liquid chromatography (HPLC) confirmed that prometryne could be oxidized by a Baeyer-Villiger monooxygenase (BVMO) encoded by a gene in the chromosome of strain DY-1. The result of gene knock-out suggested that the sulfate starvation-induced (SSI) genes in this strain might also involve in the process of prometryne degradation. These results would provide the molecular basis for the application of strain DY-1 in various fields and would contribute to the study of prometryne biodegradation mechanism as well.

Small RNA-mediated Cry toxin silencing allows Bacillus thuringiensis to evade Caenorhabditis elegans avoidance behavioral defenses

Pathogen avoidance behavior protects animal hosts against microbial pathogens. Pathogens have evolved specific strategies during coevolution in response to such host defenses. However, these strategies for combatting host avoidance behavioral defenses remain poorly understood. Here, we used Caenorhabditis elegans and its bacterial pathogen Bacillus thuringiensis as a model and determined that small RNA (sRNA)-mediated Cry toxin silencing allowed pathogens to evade host avoidance behavioral defenses. The B. thuringiensis strain YBT-1518, which encodes three nematicidal cry genes, is highly toxic to C. elegans. However, the expression of the most potent toxin, Cry5Ba, was silenced in this strain when YBT-1518 was outside the host. Cry5Ba silencing was due to the sRNA BtsR1, which bound to the RBS site of the cry5Ba transcript via direct base pairing and inhibited Cry5Ba expression. Upon ingestion by C. elegans, Cry5Ba was expressed in vivo by strain YBT-1518. Cry5Ba silencing may allow B. thuringiensis to avoid nematode behavioral defenses and then express toxins once ingested to kill the host and gain a survival advantage. Our work describes a novel model of sRNA-mediated regulation to aid pathogens in combating host avoidance behavioral defenses.

Effects of bacterial-feeding nematodes on soil microbial activity and the microbial community in oil-contaminated soil

Rapid economic development has caused an increase in serious pollution problems due to the ever-increasing use of oil and its products, thus making oil pollution control an urgent task. Studies have shown that large amounts of bacterial-feeding nematodes are present in oil-contaminated soil; their function is as yet unclear. In this experiment, different densities of Caenorhabditis elegans (C. elegans) were inoculated into artificially simulated oil-contaminated soil to examine their effects on microbial activity and the microbial community in oil-contaminated soil. Six treatments were investigated: sterilized oil-contaminated soil as control 1 (FSP), nematode-free soil as control 2 (S), oil-contaminated soil (SP), oil-contaminated soil + 5, 10 or 20 individual C. elegans per gram of dry soil (i.e., SPN5, SPN10, SPN20). Results showed that oil pollution significantly increased the soil basal respiration. However, C. elegans weakened the soil basal respiration to different degrees and soil microbial respiration entropy essentially changed in line with the soil basal respiration. Oil pollution and C. elegans boosted catalase activity in contaminated soil by approximately 64.2-145.1%. Soil urease activity of SPN5, SPN10 and SPN20 was 88.5%, 126.7% and 109.0% stronger, respectively, than that of SP. The inoculation of C. elegans changed the microbial phospholipid fatty acid content in the oil-contaminated soil, including soil bacteria, fungi, actinomycetes, Gram-positive bacteria (G⁺) and Gram-negative bacteria (G^-). Therefore, this research demonstrates that C. elegans can stimulate microbial reproduction in oil-contaminated soil, enhance related soil enzyme activities and regulate soil microbial community structure and diversity, thereby improving the contaminated soil environment and promoting oil degradation.

Effects of bacterial-feeding nematodes and organic matter on microbial activity and oil degradation in contaminated soil

Increasing rates of oil exploitation and utilization are associated with increasing rates of oil pollution in soil. Nematodes are abundant in soils with or without oil contamination, among which bacterial-feeding nematodes are the dominant group. However, their function in oil-contaminated soil is unclear. This study explores the effects of bacterial-feeding nematode and organic matter addition on microbial activity and oil degradation in contaminated soil. Experiments were conducted using six treatments of oil-contaminated soil: sterilized (Control), nematode-free (OC), nematode addition (OCN), nematode + wheat straw addition (OCNW), nematode + rapeseed cake addition (OCNR), and nematode + biochar addition (OCNB). At the end of a 168-day incubation experiment, the oil concentration of OCN soil was 26.77% lower than that of OC soil, and those of OCNW, OCNR, and OCNB were 12.83%, 27.81%, and 4.77% lower, respectively, than that of OCN soil. Over the experiment, soil microbial biomass carbon, fluorescein diacetate hydrolysis activity, and dehydrogenase activity increased by 4.35-382.30%, 1.75-302.22%, and - 2.73-224.55%, respectively, in oil-contaminated soils, with or without nematode and organic matter addition. These results suggest that the addition of organic matter and bacterial-feeding nematodes to oil-contaminated soil can promote the growth and activity of microorganisms that break down oil.

Genetic and Biochemical Characterization of a Gene Operon for trans-Aconitic Acid, a Novel Nematicide from Bacillus thuringiensis

trans-Aconitic acid (TAA) is an isomer of cis-aconitic acid (CAA), an intermediate of the tricarboxylic acid cycle that is synthesized by aconitase. Although TAA production has been detected in bacteria and plants for many years and is known to be a potent inhibitor of aconitase, its biosynthetic origins and the physiological relevance of its activity have remained unclear. We have serendipitously uncovered key information relevant to both of these questions. Specifically, in a search for novel nematicidal factors from Bacillus thuringiensis, a significant nematode pathogen harboring many protein virulence factors, we discovered a high yielding component that showed activity against the plant-parasitic nematode Meloidogyne incognita and surprisingly identified it as TAA. Comparison with CAA, which displayed a much weaker nematicidal effect, suggested that TAA is specifically synthesized by B. thuringiensis as a virulence factor. Analysis of mutants deficient in plasmids that were anticipated to encode virulence factors allowed us to isolate a TAA biosynthesis-related (tbr) operon consisting of two genes, tbrA and tbrB We expressed the corresponding proteins, TbrA and TbrB, and characterized them as an aconitate isomerase and TAA transporter, respectively. Bioinformatics analysis of the TAA biosynthetic gene cluster revealed the association of the TAA genes with transposable elements relevant for horizontal gene transfer as well as a distribution across B. cereus bacteria and other B. thuringiensis strains, suggesting a general role for TAA in the interactions of B. cereus group bacteria with nematode hosts in the soil environment. This study reveals new bioactivity for TAA and the TAA biosynthetic pathway, improving our understanding of virulence factors employed by B. thuringiensis pathogenesis and providing potential implications for nematode management applications.

Effect of humic acid on prometryn bioaccumulation and the induction of oxidative stress in zebrafish (Danio rerio)

HA made the toxicity of prometryn stronger and then weaker to Danio rerio during 1∼40 days.

Bacillus thuringiensis metalloproteinase Bmp1 functions as a nematicidal virulence factor

Some Bacillus thuringiensis strains have high toxicity to nematodes. Nematicidal activity has been found in several families of crystal proteins, such as Cry5, Cry6, and Cry55. The B. thuringiensis strain YBT-1518 has three cry genes that have high nematicidal activity. The whole genome sequence of this strain contains multiple potential virulence factors. To evaluate the pathogenic potential of virulence factors, we focused on a metalloproteinase called Bmp1. It encompasses a consecutive N-terminal signal peptide, an FTP superfamily domain, an M4 neutral protease GluZincin superfamily, two Big-3 superfamily motifs, and a Gram-positive anchor superfamily motif as a C-terminal domain. Here, we showed that purified Bmp1 protein showed metalloproteinase activity and toxicity against Caenorhabditis elegans (the 50% lethal concentration is 610 ± 9.37 μg/ml). In addition, mixing Cry5Ba with Bmp1 protein enhanced the toxicity 7.9-fold (the expected toxicity of the two proteins calculated from their separate toxicities) against C. elegans. Confocal microscopic observation revealed that Bmp1 protein was detected from around the mouth and esophagus to the intestine. Striking microscopic images revealed that Bmp1 degrades intestine tissues, and the Cry5Ba causes intestinal shrinkage from the body wall. Thus, the B. thuringiensis Bmp1 metalloproteinase is a nematicidal virulence factor. These findings give a new insight into the relationship between B. thuringiensis and its host nematodes.