The effect of paclobutrazol on soil bacterial composition across three consecutive flowering stages of mung bean

Effects of different concentrations of chlormequat chloride on bacterial community composition and diversity in peanut soil

The application of pesticides may have significant impacts on soil environment and communities. In order to understand the deep relationship between the application of chlormequat chloride (CC) and the bacterial community in peanut soil, high-resolution characterization was performed using peanut soil samples (12 points; 0-20 cm rhizosphere soil) from untreated and sprayed with different concentrations of CC. Experimental data showed that with the increase of concentration, operational taxonomic units (OTUs) richness showed a decreasing tendency. The OTUs richness at low concentration (D, 50% CC diluted 5000 times, 45 g ai/ha), medium concentration (M, 50% CC diluted 300 times, 75 g ai/ha), and high concentration (G, 50% CC diluted 1000 times, 225 g ai/ha) were 5583, 5430, and 3910, respectively. Low concentrations increased the composition and relative abundance of soil bacterial communities. In contrast, high concentrations significantly reduced bacterial diversity. As the concentration of CC increases, the abundance of Proteobacteria decreases, while the abundance of Firmicutes and Bacteroidetes increases. The number of Acidobacterium and Bacteroidetes increased in groups D and M, while it decreased in group G. D, M and G groups showed a decrease in the abundance of Pseudomonas, polaromonas, and Azovibrio compared to CK, while the abundance of Flavobacterium increased. In addition, the abundance of Rahnella1 decreased in groups D and M, while the abundance increased in group G. The main metabolic pathways included the metabolisms of nucleotides, terpenoids, polyketides, other amino acids, cofactors, vitamins, lipids, glycan biosynthesis, energy, carbohydrates, xenobiotics, amino acids, and other secondary metabolites.

Paraflavitalea pollutisoli sp. nov., Pollutibacter soli gen. nov. sp. nov., Polluticoccus soli gen. nov. sp. nov., and Terrimonas pollutisoli sp. nov., four new members of the family Chitinophagaceae from polluted soil

A taxonomic investigation was conducted on four bacterial strains isolated from soil contaminated with polycyclic aromatic hydrocarbons and heavy metals. Phylogenetic analysis revealed that these strains belonged to the family Chitinophagaceae. Examination of the 16S rRNA genes indicated that their sequence identities were below 97.6 % compared to any known and validly nominated bacterial species. The genomes of the four strains ranged from 4.12 to 8.76 Mb, with overall G + C molar contents varying from 41.28 % to 50.39 %. Predominant cellular fatty acids included iso-C15:0, iso-C15:1 G, and iso-C17:0 3-OH. The average nucleotide identity ranged from 66.90 % to 74.63 %, and digital DNA-DNA hybridization was 12.5-12.8 %. Based on the genomic and phenotypic features of the new strains, four novel species and two new genera were proposed within the family Chitinophagaceae. The ecological distributions were investigated by data-mining of NCBI databases, and results showed that additional strains or species of the newly proposed taxa were widely distributed in various environments, including polluted soil and waters. Functional analysis demonstrated that strains H1-2-19XT, JS81T, and JY13-12T exhibited resistance to arsenite (III) and chromate (VI). The proposed names for the four novel species are Paraflavitalea pollutisoli (type strain H1-2-19XT = JCM 36460T = CGMCC 1.61321T), Terrimonas pollutisoli (type strain H1YJ31T = JCM 36215T = CGMCC 1.61343T), Pollutibacter soli (type strain JS81T = JCM 36462T = CGMCC 1.61338T), and Polluticoccus soli (type strain JY13-12T = JCM 36463T = CGMCC 1.61341T).

Exploration of Klebsiella pneumoniae M6 for paclobutrazol degradation, plant growth attributes, and biocontrol action under subtropical ecosystem

In recent times, injudicious use of paclobutrazol (PBZ) in mango orchards deteriorates the soil quality and fertility by persistence nature and causes a serious ecosystem imbalance. In this study, a new Klebsiella pneumoniae strain M6 (MW228061) was isolated from mango rhizosphere and characterized as a potent plant growth promoter, biocontrol, and PBZ degrading agent. The strain M6 efficiently utilizes PBZ as carbon, energy and nitrogen source and degrades up to 98.28% (50 mgL^-1 initial conc.) of PBZ at 15^th day of incubation in MS medium. In the soil system first order degradation kinetics and linear model suggested 4.5 days was the theoretical half-life (t_1/2 value) of PBZ with strain M6. Box Behnken design (BBD) model of Response surface methodology (RSM) showed pH 7.0, 31°C temperature, and 2.0 ml inoculum size (8 x 10⁹ CFU mL^-1) was optimized condition for maximum PBZ degradation with strain M6. Plant growth promoting attributes such as Zn, K, PO₄ solubilization IAA, HCN and NH₃ production of strain M6 showed positive results and were assessed quantitatively. The relation between plant growth promotion and PBZ degradation was analyzed by heat map, principal component analysis (PCA) and, clustal correlation analysis (CCA). Strain M6 was also showing a significant biocontrol activity against pathogenic fungi such as Fusarium oxysporum (MTCC–284), Colletotrichum gloeosporioides (MTCC– 2190), Pythium aphanidermatum (MTCC– 1024), Tropical race 1 (TR -1), and Tropical race 4 (TR -4). Hence, results of the study suggested that strain M6 can be utilized as an effective bio-agent to restore degraded land affected by persistent use of paclobutrazol.

Chiral enantiomers of the plant growth regulator paclobutrazol selectively affect community structure and diversity of soil microorganisms

Paclobutrazol is a triazole plant growth regulator with a wide range of applications in crop and fruit tree production. Paclobutrazol is used as a racemic mixture in agriculture. However, the effects of paclobutrazol enantiomers on soil microbial community structure and diversity are unclear. In the present study, Illumina high-throughput sequencing was used to study the enantioselective effects of two paclobutrazol enantiomers on soil microbial community. S-paclobutrazol was more persistent than R-paclobutrazol. The half-lives of the S- and R-isomers were 80 d and 50 d, respectively. No interconversion between the two isomers occurred in soils. In addition, the enantiomers had significant enantiomeric effects on soil microbial community and the paclobutrazol degradation was probably attributed to the presence of Pseudomonas and Mycobacterium. Notably, the relative abundance of Fusarium, a genus of filamentous fungi producing gibberellins, could be enantioselectively affected by the chiral enantiomers. Paclobutrazol enantiomers exhibited greater effects on the fungal community structure than bacterial community structure due to the fungicidal activity of paclobutrazol. Finally, R-paclobutrazol had a significant effect on the microbial networks. The findings of the present study suggest that the use of S-paclobutrazol may accomplish both plant growth regulation and the minimization of effects of paclobutrazol on soil microbial communities.

Mechanisms and kinetics for the degradation of paclobutrazol and biocontrol action of a novel Pseudomonas putida strain T7

The present study explores biodegradation kinetics and process optimization of plant growth retardant from triazole group paclobutrazol (PBZ; C₁₅H₂₀ClN₃O mol. wt. 293.79 g mol^-1) in a batch experiment. A gram-negative rod-shaped bacterium T7 was isolated from PBZ applied agricultural field by enrichment technique and characterized as Pseudomonas putida strain T7. Strain was tested for PBZ biodegradation and plant growth-promoting characteristics. Results revealed that strain T7 utilizes PBZ as a carbon and energy source and showing degradation up to 98.30% on the 15th day. First-order degradation kinetics and a linear model were well fitted and showing a maximum t_1/2 value on 9th day. Biodegradation optimization by Box Behnken design (BBD) of Response surface methodology (RSM) showed maximum degradation at pH 7.0, 31 °C temperature, and 2 mL inoculum size (8 × 10⁹ CFU mL^-1). The bacterium was also able to solubilize Zn, K, and PO₄ and produced a copious amount of IAA, HCN, and Ammonia. The biocontrol activity against plant pathogens like Fusarium oxysporum (MTCC-284), Colletotrichum gloeosporioides (MTCC 2190), Pythium aphanidermatum (MTCC - 1024), Tropical race-1 (TR -1), and Tropical race - 4 (TR-4) showed the great antagonistic effect. Hence, this strain can be employed as an effective bio-agent for eco-friendly cleanup strategies and pathogen suppressive agents in paclobutrazol contaminated soil.

Triazole fungicides in soil affect the yield of fruit, green biomass, and phenolics production of Solanum lycopersicum L

A part of the fungicides used in foliar treatment penetrates into the soil. This study describes changes in the bioavailability of (essential) elements in soil, fructification, the amount of green biomass and the production of phenolic compounds related solely to the presence of triazoles (penconazole and cyproconazole) in soil, injected as a single compound or their mixture. The triazoles presence has substantially affected the bioavailability of Fe, Cu and Zn in soil. The amount of green biomass has significantly decreased, whereas the chlorophylls a and b have not been affected. As a potential mark of plant stress, the fruits of the treated variants are significantly bigger. The content of phenolics in tomato peel (e.g. quercetin, quercitrin, hesperidin, naringin, and chlorogenic, salicylic and p-coumaric acid) has been quantified. The biggest changes (increase/decrease) have been observed in the contents of p-coumaric and chlorogenic acid, quercetin and quercitrin.

The potential risks of paclobutrazol residue on yogurt fermentation from the level of chiral enantiomers

In recent years, pesticide residues in food have increasingly become the focus of public attention. However, the standard system of pesticide maximum residue limits in fermented food is imperfect, which can lead to potential safety risks to consumers. In this context, the aim of the study was to assess the potential effects of paclobutrazol residue on the yogurt fermentation process. We examined the stereoselective behaviors of the 2 paclobutrazol enantiomers from the perspective of chirality during the yogurt fermentation process. The results indicated that no significant degradation occurred for either of the 2 enantiomers (2R, 3R-paclobutrazol, 2S, 3S-paclobutrazol), and no visible enantiomer conversion behavior was observed. In addition, the reason paclobutrazol did not significantly degrade was explained from the perspective of the microbial function. Results from 16S rRNA sequencing indicated that paclobutrazol significantly affected the microbial composition and inhibited metabolic function of microorganisms to exogenous substances, which impeded the degradation of residual pesticide in yogurt. Furthermore, the stable residue of exogenous substance may cause potential food safety problems. Microbial α-diversity analysis indicated that fermentation time played a more important role on diversity than did paclobutrazol concentration. Moreover, Staphylococcus was found in yogurt after treatment with paclobutrazol; Staphylococcus aureus causes dangerous infectious diseases in humans. We devised a method to investigate the presence of pesticide residues during food fermentation and provided a theoretical basis for food safety assessment.

Bioinoculants play a significant role in shaping the rhizospheric microbial community: a field study with Cajanus cajan

The present study is an attempt to understand the impact of bioinoculants, Azotobacter chroococcum (A), Bacillus megaterium (B), Pseudomonas fluorescens (P), on (a) soil and plant nutrient status, (b) total resident and active bacterial communities, and (c) genes and transcripts involved in nitrogen cycle, during cultivation of Cajanus cajan. In terms of available macro- and micro-nutrients, triple inoculation of the bioinoculants (ABP) competed well with chemical fertilizer (CF). Their 'non-target' effects were assessed in terms of the abundance and activity of the resident bacterial community by employing denaturing gradient gel electrophoresis (DGGE). The resident bacterial community (16S rRNA gene) was stable, while the active fraction (16S rRNA transcripts) was influenced (in terms of abundance) by the treatments. Quantification of the genes and transcripts involved in N cycle by qPCR revealed an increase in the transcripts of nifH in the soil treated with ABP over CF, with an enhancement of 3.36- and 1.57- fold at flowering and maturity stages of plant growth, respectively. The bioinoculants shaped the resident microflora towards a more beneficial community, which helped in increasing soil N turnover and hence, soil fertility as a whole.

Environmental behavior of paclobutrazol in soil and its toxicity on potato and taro plants

The environmental behavior of paclobutrazol in soil and its toxicity were studied by field investigation and an outdoor pot experiment, and the residue of paclobutrazol was detected by gas chromatography-mass spectrometry. Field investigation has found that the residual paclobutrazol in the former succession crop could severely inhibit the growth of succeeding crops of potato; with migration and transformation of residual paclobutrazol in the soil, the stems of potato were thickened with residual amount of 1.23 mg kg^-1, the growth was slow, and the height of potato in soil with residual amount of 1.34 mg kg^-1 and the control was significantly different. The degradation dynamics of paclobutrazol fits with the first-order degradation kinetics, although T_1/2 of paclobutrazol of the taro planting soil was 30.14-46.21 days and the residual paclobutrazol remained detectable even on day 120 after application. Taro leaves were sensitive to the stress of paclobutrazol pollution; the taro leaf thickness increased, the leaf area decreased, the chlorophyll content per area unit of taro leaf showed an obvious increased trend, and SOD and CAT activities and MDA and proline content increased significantly. Paclobutrazol promoted the tillering of taro, and the taro seedlings were dwarfed by 58.01, 63.27, and 75.88% at different concentrations. It indicated that taro had strong stress response ability under paclobutrazol pollution.