Owing to their reproducibility, stability, and cost-effective production, the recombinant variable domains of heavy-chain-only antibodies (VHHs) are becoming a salient option as immunoassay reagents. Recently, there have been several reports describing their application to the detection of small molecules (haptens). However, lacking the heavy-light chain interface of conventional antibodies, VHHs are not particularly apt to bind small analytes and failures are not uncommon. Here we describe the construction of a VHH phage display library against the cyanobacterial hepatotoxin microcystin LR and its selection using competitive panning and two novel panning strategies. The outcome of each strategy was evaluated by a large-scale screening using in vivo biotinylated nanobodies. The three methods selected for different nonoverlapping subsets of VHHs, allowing one to optimize the immunodetection of the toxin. The best results were obtained by promoting the isolation of VHHs with the slowest k (off-rate selection). Among these, the biotinylated nanobody A2.3 performed in ELISA with excellent recovery and high sensitivity, IC50 = 0.28 μg/L, with a limit of detection that is well below the most rigorous guidelines for the toxin. While it may be case-specific, these results highlight the importance of exploring different panning strategies to optimize the selection of antihapten nanobodies.

The first total synthesis of cyclopeptides versicotide E and F, natural products produced by marine fungus Aspergillus versicolor LZD-14-1, was achieved in good yield by solid phase peptide synthesis (SPPS) of their linear precursors and solution phase cyclization. All the versicotides AÀ F were evaluated as herbicides and inhibitors of cyanobacterial growth. Versicotides A, B, D, E and F showed a significant inhibition of Rye grass seed's radicle growth at a concentration of 67 μg/mL. Versicotides A, B and D also inhibited seed germination and leaf development. On the other hand, Versicotides D and F caused a relevant reduction on Microcystis aeruginosa population when cultures on exponential growth were incubated with 40 μg/mL solutions of these compounds. Evaluation of the concentration of microcystins after these treatments showed that versicotide D inhibited the production of microcystins in a comparable extent to the positive control, colistine. These results indicate versicotides, with versicotides D and F as top hits, could be considered as lead candidates in the development of bioherbicides able to mitigate the environmental impact that the evolution of agriculture has had on water quality.

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The development of simple, reliable, and cost-effective methods is critically important to study the spatial and temporal variation of microcystins (MCs) in the food chain. Nanobodies (Nbs), antigen binding fragments from camelid antibodies, present valuable features for analytical applications. Their small antigen binding site offers a focused recognition of small analytes, reducing spurious cross-reactivity and matrix effects. A high affinity and broad cross-reactivity anti-MCs-Nb, from a llama antibody library, was validated in enzyme linked immunosorbent assay (ELISA), and bound to magnetic particles with an internal standard for pre-concentration in quantitative-matrix-assisted laser desorption ionization-time of flight mass spectrometry (Nb-QMALDI MS). Both methods are easy and fast; ELISA provides a global result, while Nb-QMALDI MS allows for the quantification of individual congeners and showed excellent performance in the fish muscle extracts. The ELISA assay range was 1.8–29 ng/g and for Nb-QMALDI, it was 0.29–29 ng/g fish ww. Fifty-five fish from a MC-containing dam were analyzed by both methods. The correlation ELISA/sum of the MC congeners by Nb-QMALDI-MS was very high (r Spearman = 0.9645, p < 0.0001). Using ROC curves, ELISA cut-off limits were defined to accurately predict the sum of MCs by Nb-QMALDI-MS (100% sensitivity; ≥89% specificity). Both methods were shown to be simple and efficient for screening MCs in fish muscle to prioritize samples for confirmatory methods.

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