Competitiveness of reutericyclin producing and nonproducing Limosilactobacillus reuteri in food and intestinal ecosystems: a game of rock, paper, and scissors?

The ecological relationships among antimicrobial producing, resistant, and sensitive strains have been proposed to follow rock-paper-scissors dynamics, but evidence is mainly based on Gram-negative bacteriocins in vitro. The ecological relevance of antimicrobials in vivo or in situ has not been systematically studied. This study therefore aimed to analyze binary and ternary competitions among reutericyclin-producing strain Limosilactobacillus reuteri TMW1.656, its reutericyclin-resistant, nonproducing isogenic derivative L. reuteri TMW1.656∆rtcN, and the reutericyclin-sensitive, nonproducing L. reuteri TMW1.656∆rtcN∆rtcT in vitro (liquid culture and static plate), in situ (sourdough fermentation), and in vivo (gut of germ-free mice). In liquid culture, L. reuteri TMW1.656 had a higher fitness than TMW1.656∆rtcN and TMW1.656∆rtcN∆rtcT. Limosilactobacillus reuteri TMW1.656∆rtcN∆rtcT had a higher fitness than TMW1.656∆rtcN. On agar plates, L. reuteri TMW1.656 had a higher fitness than TMW1.656∆rtcN∆rtcT. In situ, reutericyclin production and resistance had no influence on the fitness of the strains. In vivo, TMW1.656 had an advantage over TMW1.656∆rtcN and TMW1.656∆rtcN∆rtcT. Ternary competitions showed reutericyclin production was ecologically beneficial in all ecosystems. The findings support the ecological importance of reutericyclin in a variety of environments/niches, providing an explanation for the acquisition of the reutericyclin gene cluster in L. reuteri and its contribution to the ecological fitness of Streptococcus mutans.

The fate of mycotoxins in oranges during storage and processing

To evaluate the safety of orange consumption induced by mycotoxins, 'Newhall' navel oranges were artificially inoculated with P. expansum and A. tenuissima, followed by an evaluation of the distribution and migration patterns of corresponding mycotoxins (patulin [PAT], tentoxin [Ten], altenuene [ALT], alternariol monomethyl ether [AME], alternariol [AOH] and tenuazonic acid [TeA]) during orange storage and processing. The concentration of mycotoxins decreased as the increase of distance from the lesion, and mycotoxins could be detected throughout the orange when the lesion extended to 8 mm in diameter. AOH and AME pose the primary source of dietary risk with high concentrations and low thresholds of toxicological concern. Orange juice and pectin processing could remove 43.4-98.7% of mycotoxins, while tangerine peelprocessing might lead to significant enrichment of mycotoxins with the processing factors (PFs) of 2.8-3.5. The findings may offer scientific insights into mitigating the dietary risk of mycotoxin exposure from oranges and their derivatives.

Enhanced Non-Toxic Immunodetection of Alternaria Mycotoxin Tenuazonic Acid Based on Ferritin-Displayed Anti-Idiotypic Nanobody-Nanoluciferase Multimers

The non-toxic immunoassay for mycotoxins is being paid more attention due to its advantages of higher safety and cost savings by using anti-idiotype antibodies to substitute toxins. In this study, with tenuazonic acid (TeA), a kind of highly toxic Alternaria mycotoxin as the target, an enhanced non-toxic immunoassay was developed based on the ferritin-displayed anti-idiotypic nanobody-nanoluciferase multimers. First, three specific β-type anti-idiotype nanobodies (AId-Nbs) bearing the internal image of TeA mycotoxin were selected from an immune phage display library. Then, the AId-Nb 2D with the best performance was exploited to generate a nanoluciferase (Nluc)-functionalized fusion monomer, by which a one-step non-toxic immunodetection format for TeA was established and proven to be effective. To further improve the affinity of the monomer, a ferritin display strategy was used to prepare 2D-Nluc fusion multimers. Finally, an enhanced bioluminescent enzyme immunoassay (BLEIA) was established in which the half maximal inhibitory concentration (IC₅₀) for TeA was 6.5 ng/mL with a 10.5-fold improvement of the 2D-based enzyme-linked immunosorbent assay (ELISA). The proposed assay exhibited high selectivities and good recoveries of 80.0-95.2%. The generated AId-Nb and ferritin-displayed AId-Nb-Nluc multimers were successfully extended to the application of TeA in food samples. This study brings a new strategy for production of multivalent AId-Nbs and non-toxic immunoassays for trace toxic contaminants.

Tenuazonic acid from Stemphylium loti inhibits the plant plasma membrane H+ -ATPase by a mechanism involving the C-terminal regulatory domain

Pathogenic fungi often target the plant plasma membrane (PM) H+ -ATPase during infection. To identify pathogenic compounds targeting plant H+ -ATPases, we screened extracts from 10 Stemphylium species for their effect on H+ -ATPase activity. We identified Stemphylium loti extracts as potential H+ -ATPase inhibitors, and through chemical separation and analysis, tenuazonic acid (TeA) as a potent H+ -ATPase inhibitor. By assaying ATP hydrolysis and H+ pumping, we confirmed TeA as a H+ -ATPase inhibitor both in vitro and in vivo. To visualize in planta inhibition of the H+ -ATPase, we treated pH-sensing Arabidopsis thaliana seedlings with TeA and quantified apoplastic alkalization. TeA affected both ATPase hydrolysis and H+ pumping, supporting a direct effect on the H+ -ATPase. We demonstrated apoplastic alkalization of A. thaliana seedlings after short-term TeA treatment, indicating that TeA effectively inhibits plant PM H+ -ATPase in planta. TeA-induced inhibition was highly dependent on the regulatory C-terminal domain of the plant H+ -ATPase. Stemphylium loti is a phytopathogenic fungus. Inhibiting the plant PM H+ -ATPase results in membrane potential depolarization and eventually necrosis. The corresponding fungal H+ -ATPase, PMA1, is less affected by TeA when comparing native preparations. Fungi are thus able to target an essential plant enzyme without causing self-toxicity.

Fungal contamination and selected mycotoxins in pre- and post-harvest maize in Honduras

Sixty nine samples of maize were collected from pre-harvest standing crops and on-farm storage facilities from 52 smallholder farms located within 4 regions of Honduras during October 1992 and November 1993. Samples were visually assessed for insect damage and fungal spoilage, and the mycoflora quantified on artificial media. The major components of the ear rot complex were: Fusarium moniliforme, F. moniliforme var. subglutinans, Penicillium species, Stenocarpella maydis, S. macrospora and Acremonium spp. Representative samples were also assayed for mycotoxin content. Fumonisin B1 was detected in all 24 samples tested at levels of between 68-6,555 (micrograms/kg), and aflatoxin was detected in 2 samples heavily contaminated with Aspergillus flavus. Moniliformin and tenuazonic acid were not detected in the samples tested. The implications of these findings for human and livestock health risk are discussed, together with possible strategies for controlling these pathogens.

Complexation of the fungal metabolite tenuazonic acid with copper (II), iron (III), nickel (II), and magnesium (II) ions

Tenuazonic acid (TA) is a phytotoxin produced by a fungal pathogen of rice, Pyricularia oryzae. We have synthesized and characterized the metal complexes of TA with copper (II), iron (III), nickel (II), and magnesium (II). The stoichiometry of the complexes determined by microanalysis and mass spectroscopy (D/CI) are Cu(II)TA2, Fe(III)TA3, Ni(II)TA2, and Mg(TA)2. Voltammograms of Fe(III)TA3, and Cu(II)TA2 in methanolic solutions confirmed this stoichiometry. Ni(II)TA2 paramagnetism and visible absorption data suggest an octahedral geometry. Fe(III)TA3 showed a characteristic visible absorption at 450 nm. Addition of Fe(III)Cl3 and Mg(II)Cl2 did not reverse the toxicity of NaTA to rice and bacterial cells, showing that this toxicity is not due to the privation of the cells of these metals essential for cell growth.