Bacterial challenge-associated metabolic phenotypes in Hermetia illucens defining nutritional and functional benefits

Black soldier fly (BSF, Hermetia illucens) is popular for its applications in animal feed, waste management and antimicrobial peptide source. The major advantages of BSF larva include their robust immune system and high nutritional content that can be further developed into more potential agricultural and medical applications. Several strategies are now being developed to exploit their fullest capabilities and one of these is the immunity modulation using bacterial challenges. The mechanism underlying metabolic responses of BSF to different bacteria has, however, remained unclear. In the current study, entometabolomics was employed to investigate the metabolic phenoconversion in response to either Escherichia coli, Staphylococcus aureus, or combined challenges in BSF larva. We have, thus far, characterised 37 metabolites in BSF larva challenged with different bacteria with the major biochemical groups consisting of amino acids, organic acids, and sugars. The distinct defense mechanism-specific metabolic phenotypes were clearly observed. The combined challenge contributed to the most significant metabolic phenoconversion in BSF larva with the dominant metabolic phenotypes induced by S. aureus. Our study suggested that the accumulation of energy-related metabolites provided by amino acid catabolism is the principal metabolic pathway regulating the defense mechanism. Therefore, combined challenge is strongly recommended for raising BSF immunity as it remarkably triggered amino acid metabolisms including arginine and proline metabolism and alanine, aspartate and glutamate metabolism along with purine metabolism and pyruvate metabolism that potentially result in the production of various nutritional and functional metabolites.

An Integrative Transcriptomic and Metabolomic Analysis of Red Pitaya (Hylocereus polyrhizus) Seedlings in Response to Heat Stress

Red pitaya (Hylocereus polyrhizus) is a significant functional food that is largely planted in Southeast Asia. Heat stress (HS) induced by high temperatures is likely to restrict the growth and survival of red pitaya. Although pitaya can tolerate temperatures as high as 40 °C, little is known of how it can withstand HS. In this study, the transcriptomic and metabolomic responses of red pitaya seedlings to HS were analyzed. A total of 198 transcripts (122 upregulated and 76 downregulated) were significantly differentially expressed after 24 h and 72 h of exposure to 42 °C compared with a control grown at 28 °C. We also identified 64 differentially accumulated metabolites in pitaya under HS (37 increased and 27 decreased). These differential metabolites, especially amino acids, organic acids, and sugars, are involved in metabolic pathways and the biosynthesis of amino acids. Interaction network analysis of the heat-responsive genes and metabolites suggested that similar pathways and complex response mechanisms are involved in the response of pitaya to HS. Overexpression of one of the upregulated genes (contig10820) in Arabidopsis, which is a homolog of PR-1 and named HuPR-1, significantly increased tolerance to HS. This is the first study showing that HuPR-1 plays a role in the response of pitaya to abiotic stress. These findings provide valuable insights that will aid future studies examining adaptation to HS in pitaya.

Effects of Association of Barley Plants with Hydrocarbon-Degrading Bacteria on the Content of Soluble Organic Compounds in Clean and Oil-Contaminated Sand

Plant-bacteria consortia are more effective in bioremediation of petroleum contaminated soil than when either organism is used individually. The reason for this is that plant root exudates promote growth and activity of oil degrading bacteria. However, insufficient attention has been paid to the ability of bacteria to influence root exudation. Therefore, the influence of barley plants and/or bacterial inoculation (Pseudomonas hunanensis IB C7 and Enterobacter sp. UOM 3) on the content of organic acids, sugars and plant hormones in the eluate from clean and oil-polluted sand was studied separately or in combination. These strains are capable of oxidizing hydrocarbons and synthesizing auxins. Concentrations of organic acids and sugars were determined using capillary electrophoresis, and hormones by enzyme-linked immunosorbent assays. In the absence of plants, no sugars were detected in the sand, confirming that root exudates are their main source. Introducing bacteria into the sand increased total contents of organic compounds both in the presence and absence of oil. This increase could be related to the increase in auxin amounts in the sand eluate, as well as in plants. The results indicate that bacteria are able to increase the level of root exudation. Since auxins can promote root exudation, bacterial production of this hormone is likely responsible for increased concentrations of soluble organic compounds in the sand. Bacterial mediation of root exudation by affecting plant hormonal status should be considered when choosing microorganisms for phytoremediation.

Simultaneous determination of organic acids and sugars in fruit juices by High performance liquid chromatography: characterization and differentiation of commercial juices by principal component analysis

ABSTRACT: The present research presents an analytical methodology based on High Performance Liquid Chromatography (HPLC) and Principal Component Analyses (PCA) for simultaneous quantification and analytical differentiation of organic acids and sugars in commercial fruit juice samples (orange, grape, apple and tangerine). In addition to the development of the method that generated suitable validation paramters for quantitative analytical applications, the analysis of fourteen commercial samples and the use of Principal Component Analysis indicated the relationship between the constituents and the very constitutional chemical nature of the juice. In general, in grape and apple juices, ascorbic acid was not quantified and the citric acid content was very low; however, the concentrations of fructose and glucose were the highest in both juices. In orange and mandarin orange juices, the content of all analytes, except acorbic acid, did not differ statistically from each other. However, these differed significantly from the others, mainly in relation to sucrose content. Finally, the apple juice samples differed according to the content of fructose and malic acid, the predominant constituint of the apple. Results showed that the simultaneous chromatographic method associated with principal component analysis generated important information about characteristics of commercial juices, with the potential to be used in systems of quality control and identification of adulterations.

Characterization of cold stress responses in different rapeseed ecotypes based on metabolomics and transcriptomics analyses

The winter oilseed ecotype is more tolerant to low temperature than the spring ecotype. Transcriptome and metabolome analyses of leaf samples of five spring Brassica napus L. (B. napus) ecotype lines and five winter B. napus ecotype lines treated at 4 °C and 28 °C were performed. A total of 25,460 differentially expressed genes (DEGs) of the spring oilseed ecotype and 28,512 DEGs of the winter oilseed ecotype were identified after cold stress; there were 41 differentially expressed metabolites (DEMs) in the spring and 47 in the winter oilseed ecotypes. Moreover, more than 46.2% DEGs were commonly detected in both ecotypes, and the extent of the changes were much more pronounced in the winter than spring ecotype. By contrast, only six DEMs were detected in both the spring and winter oilseed ecotypes. Eighty-one DEMs mainly belonged to primary metabolites, including amino acids, organic acids and sugars. The large number of specific genes and metabolites emphasizes the complex regulatory mechanisms involved in the cold stress response in oilseed rape. Furthermore, these data suggest that lipid, ABA, secondary metabolism, signal transduction and transcription factors may play distinct roles in the spring and winter ecotypes in response to cold stress. Differences in gene expression and metabolite levels after cold stress treatment may have contributed to the cold tolerance of the different oilseed ecotypes.

The effect of microorganisms and heavy metals on the exudation of low molecular weight organic compounds by plant roots

The aim of our research was to study the effect of growth-promoting rhizobacteria (Pseudomonas oryzihabitans and Variovorax paradoxus) and toxic elements (Al, Cd and Hg) on the root exudation in various pea (Pisum sativum L.) genotypes. For this, methods of periodic cultures, gnotobiotic plant-microbial systems, ICPE and UPLC were used. It was established that rhizobacteria actively utilized organic acids and sugars secreted by the roots and contributed to an increase in pH and Al immobilization in the rhizosphere. Cadmium increased the exudation of many substances of pea line SGE, but this effect was more pronounced in the mutant SGECdt. Stimulation of the exudation of amino acids was detected during Hg treatment to a greater extent in wild-type SGE. The combined action of Cd and Hg did not lead to a further increase in exudation. The results obtained indicate various mechanisms of exudation of the studied fractions, while the most pronounced differences are observed between the fractions of amino acids or sugars with organic acids. Exudation of organic acids plays an important role in the decreased stability and accumulation of Hg by the pea mutant SGECdt.