The impact of insect herbivory on biogeochemical cycling in broadleaved forests varies with temperature.

Herbivorous insects alter biogeochemical cycling within forests, but the magnitude of these impacts, their global variation, and drivers of this variation remain poorly understood. To address this knowledge gap and help improve biogeochemical models, we established a global network of 74 plots within 40 mature, undisturbed broadleaved forests. We analyzed freshly senesced and green leaves for carbon, nitrogen, phosphorus and silica concentrations, foliar production and herbivory, and stand-level nutrient fluxes. We show more nutrient release by insect herbivores at non-outbreak levels in tropical forests than temperate and boreal forests, that these fluxes increase strongly with mean annual temperature, and that they exceed atmospheric deposition inputs in some localities. Thus, background levels of insect herbivory are sufficiently large to both alter ecosystem element cycling and influence terrestrial carbon cycling. Further, climate can affect interactions between natural populations of plants and herbivores with important consequences for global biogeochemical cycles across broadleaved forests.

A Critical Study on DNA Probes Attached to Microplate for CRISPR/Cas12 Trans-Cleavage Activity.

CRISPR/Cas12-based biosensors are emerging tools for diagnostics. However, their application of heterogeneous formats needs the efficient detection of Cas12 activity. We investigated DNA probes attached to the microplate surface and cleaved by Cas12a. Single-stranded (ss) DNA probes (19 variants) and combined probes with double-stranded (ds) and ssDNA parts (eight variants) were compared. The cleavage efficiency of dsDNA-probes demonstrated a bell-shaped dependence on their length, with a cleavage maximum of 50%. On the other hand, the cleavage efficiency of ssDNA probes increased monotonously, reaching 70%. The most effective ssDNA probes were integrated with fluorescein, antibodies, and peroxidase conjugates as reporters for fluorescent, lateral flow, and chemiluminescent detection. Long ssDNA probes (120-145 nt) proved the best for detecting Cas12a trans-activity for all of the tested variants. We proposed a test system for the detection of the nucleocapsid (N) gene of SARS-CoV-2 based on Cas12 and the ssDNA-probe attached to the microplate surface; its fluorescent limit of detection was 0.86 nM. Being united with pre-amplification using recombinase polymerase, the system reached a detection limit of 0.01 fM, thus confirming the effectiveness of the chosen ssDNA probe for Cas12-based biosensors.

Comparison of Single-Stranded DNA Probes Conjugated with Magnetic Particles for Trans-Cleavage in Cas12a-Based Biosensors.

Biosensors based on endonuclease Cas12 provide high specificity in pathogen detection. Sensitive detection using Cas12-based assays can be achieved using trans-cleaved DNA probes attached to simply separated carriers, such as magnetic particles (MPs). The aim of this work was to compare polyA, polyC, and polyT single-stranded (ss) DNA with different lengths (from 10 to 145 nt) as trans-target probes were immobilized on streptavidin-covered MPs. Each ssDNA probe was labeled using fluorescein (5') and biotin (3'). To compare the probes, we used guide RNAs that were programmed for the recognition of two bacterial pathogens: Dickeya solani (causing blackleg and soft rot) and Erwinia amylovora (causing fire blight). The Cas12 was activated by targeting double-stranded DNA fragments of D. solani or E. amylovora and cleaved the MP-ssDNA conjugates. The considered probes demonstrated basically different dependencies in terms of cleavage efficiency. PolyC was the most effective probe when compared to polyA or polyT probes of the same length. The minimal acceptable length for the cleavage follows the row: polyC < polyT < polyA. The efficiencies of polyC and polyT probes with optimal length were proven for the DNA targets' detection of D. solani and E. amylovora. The regularities found can be used in Cas12a-based detection of viruses, bacteria, and other DNA/RNA-containing analytes.

Engineering of DNA Structures Attached to Magnetic Particles for Effective Trans- and Cis-Cleavage in Cas12-Based Biosensors.

Sequence-specific endonuclease Cas12-based biosensors have rapidly evolved as a strong tool to detect nucleic acids. Magnetic particles (MPs) with attached DNA structures could be used as a universal platform to manipulate the DNA-cleavage activity of Cas12. Here, we propose nanostructures of trans- and cis-DNA targets immobilized on the MPs. The main advantage of the nanostructures is a rigid double-stranded DNA adaptor that distances the cleavage site from the MP surface to ensure maximum Cas12 activity. Adaptors with different lengths were compared by detecting the cleavage by fluorescence and gel electrophoresis of the released DNA fragments. The length-dependent effects for cleavage on the MPs' surface were found both for cis- and trans-targets. For trans-DNA targets with a cleavable 15-dT tail, the results showed that the optimal range of the adaptor length was 120-300 bp. For cis-targets, we varied the length and location of the adaptor (at the PAM or spacer ends) to estimate the effect of the MP's surface on the PAM-recognition process or R-loop formation. The sequential arrangement of an adaptor, PAM, and a spacer was preferred and required the minimum adaptor length of 3 bp. Thus, with cis-cleavage, the cleavage site can be located closer to the surface of the MPs than with trans-cleavage. The findings provide solutions for efficient Cas12-based biosensors using surface-attached DNA structures.

Comparison of Biosensing Methods Based on Different Isothermal Amplification Strategies: A Case Study with Erwinia amylovora.

Isothermal amplifications allow for the highly sensitive detection of nucleic acids, bypassing the use of instrumental thermal cycling. This work aimed to carry out an experimental comparison of the four most promising techniques: recombinase polymerase amplification (RPA) and loop-mediated isothermal amplification (LAMP) coupled with lateral flow test or coupled with additional amplification based on CRISPR/Cas12a resulting from the fluorescence of the Cas12a-cleaved probe. To compare the four amplification techniques, we chose the bacterial phytopathogen Erwinia amylovora (causative agent of fire blight), which has a quarantine significance in many countries and possesses a serious threat to agriculture. Three genes were chosen as the targets and primers were selected for each one (two for RPA and six for LAMP). They were functionalized by labels (biotin, fluorescein) at the 5' ends for amplicons recognition by LFT. As a result, we developed LAMP-LFT, LAMP-CRISPR/Cas, RPA-LFT, and RPA-CRISPR/Cas for E. amylovora detection. The detection limit was 104 CFU/mL for LAMP-LFT, 103 CFU/mL for LAMP-CRISPR/Cas, and 102 CFU/mL for RPA-LFT and RPA-CRISPR/Cas. The results of four developed test systems were verified by qPCR on a panel of real samples. The developed assays based on RPA, LAMP, CRISPR/Cas12a, and LFT are rapid (30-55 min), user-friendly, and highly sensitive for E. amylovora detection. All proposed detection methods can be applied to fire blight diagnosis and effective management of this disease.

SARS-CoV-2 Subunit Virus-like Vaccine Demonstrates High Safety Profile and Protective Efficacy: Preclinical Study.

Public health threat coming from a rapidly developing COVID-19 pandemic calls for developing safe and effective vaccines with innovative designs. This paper presents preclinical trial results of "Betuvax-CoV-2", a vaccine developed as a subunit vaccine containing a recombinant RBD-Fc fusion protein and betulin-based spherical virus-like nanoparticles as an adjuvant ("Betuspheres"). The study aimed to demonstrate vaccine safety in mice, rats, and Chinchilla rabbits through acute, subchronic, and reproductive toxicity studies. Along with safety, the vaccine demonstrated protective efficacy through SARS-CoV-2-neutralizing antibody production in mice, rats, hamsters, rabbits, and primates (rhesus macaque), and lung damage and infection protection in hamsters and rhesus macaque model. Eventually, "Betuvax-CoV-2" was proved to confer superior efficacy and protection against the SARS-CoV-2 in preclinical studies. Based on the above results, the vaccine was enabled to enter clinical trials that are currently underway.

Comparative study of magnetic beads and microplates as supports in heterogeneous amplified assay of miRNA-141 by using mismatched catalytic hairpin assembly reaction.

Magnetic beads (MBs) are often considered as an effective carrier in heterogeneous assays due to the simplicity of separation and washing, and the ability to increase and control the surface area. However, the effect of the MBs surface on the analytical parameters is poorly characterized and is often postulated from intuitive considerations. Herein, experimental evaluation through the comparison of MBs and microwell plate was carried out using the miRNA-141 (biomarker for cancer) as a target, the detection of which was performed by chemiluminescent assay with a homogeneous mismatched catalytic hairpin assembly (mCHA) reaction. The mCHA reaction produced double-stranded (ds) DNA labeled at one end with fluorescein (Flu) for capture with anti-Flu antibodies immobilized on a solid carrier, on the other end with biotin for recognition by streptavidin-polyperoxidase conjugate. The conditions of immobilization of anti-Flu antibody on MBs (a diameter of 440 nm) performed using a carbodiimide method were optimized by varying the antibody concentration in the reaction solution. It was shown that the dependence of chemiluminescent signal as a function of the concentration of anti-FluAb-MBs conjugates had a bell-shaped character. The maximum chemiluminescence was produced at the concentration of the conjugates of 2 × 109 particles/mL, with a surface area of 65 mm2. The identical surface area was used upon the assay performance with polystyrene microplates. Comparison of MBs- and microplate-assays for miRNA-141 determination showed that the obtained calibration curves and their detection limit values were the same and did not depend on the used carrier. The results showed that the choice of a carrier for heterogeneous assays should be guided by the convenience of the assay performance, not its surface area.

DIRECT2: A novel platform for a CRISPR-Cas12-based assay comprising universal DNA-IgG probe and a direct lateral flow test.

CRISPR-Cas12-based biosensors are a promising tool for the detection of nucleic acids. After dsDNA-target-activated Cas12 cleaves the ssDNA probe, a lateral flow test (LFT) is applied for rapid, simple, and out-of-laboratory detection of the cleaved probe. However, most of the existing approaches of LFT detection have disadvantages related to inverted test/control zones in which the assay result depends not only on the cleavage of the probe but also on the second factor: the binding of the non-cleaved probe in the control zone. We proposed a novel platform for the detection of trans-cleaved DNA using a universal DNA-IgG probe and LFT with the sequential direct location of test and control zones. The advantage of the platform consists of the assay result depending only on the cleaved probe. For this, we designed a composite probe that comprise two parts: the DNA part (biotinylated dsDNA connected to ssDNA with fluorescein) (FAM), and the antibody part (mouse anti-FAM IgG). The Cas12, with guide RNA, was activated by the dsDNA-target. The activated Cas12 cleaved the probe, releasing the ssDNA-FAM-IgG reporter that was detected by the LFT. The sandwich LFT was proposed with anti-mouse IgG adsorbed in the test zone and on the surface of gold nanoparticles. We called the platform with direct location zones and direct analyte-signal dependence the DNA-Immunoglobulin Reporter Endonuclease Cleavage Test (DIRECT2). Therefore, this proof-of-concept study demonstrated that the combination of the proposed DNA-IgG probe and direct LFT opens new opportunities for CRISPR-Cas12 activity detection and its bioanalytical applications.

Design and Immunological Properties of the Novel Subunit Virus-like Vaccine against SARS-CoV-2.

The COVID-19 pandemic is ongoing, and the need for safe and effective vaccines to prevent infection and to control spread of the virus remains urgent. Here, we report the development of a SARS-CoV-2 subunit vaccine candidate (Betuvax-CoV-2) based on RBD and SD1 domains of the spike (S) protein fused to a human IgG1 Fc fragment. The antigen is adsorbed on betulin adjuvant, forming spherical particles with a size of 100-180 nm, mimicking the size of viral particles. Here we confirm the potent immunostimulatory activity of betulin adjuvant, and demonstrate that two immunizations of mice with Betuvax-CoV-2 elicited high titers of RBD-specific antibodies. The candidate vaccine was also effective in stimulating a neutralizing antibody response and T cell immunity. The results indicate that Betuvax-CoV-2 has good potential for further development as an effective vaccine against SARS-CoV-2.

Rapid Full-Cycle Technique to Control Adulteration of Meat Products: Integration of Accelerated Sample Preparation, Recombinase Polymerase Amplification, and Test-Strip Detection.

Verifying the authenticity of food products is essential due to the recent increase in counterfeit meat-containing food products. The existing methods of detection have a number of disadvantages. Therefore, simple, cheap, and sensitive methods for detecting various types of meat are required. In this study, we propose a rapid full-cycle technique to control the chicken or pig adulteration of meat products, including 3 min of crude DNA extraction, 20 min of recombinase polymerase amplification (RPA) at 39 °C, and 10 min of lateral flow assay (LFA) detection. The cytochrome B gene was used in the developed RPA-based test for chicken and pig identification. The selected primers provided specific RPA without DNA nuclease and an additional oligonucleotide probe. As a result, RPA-LFA, based on designed fluorescein- and biotin-labeled primers, detected up to 0.2 pg total DNA per µL, which provided up to 0.001% w/w identification of the target meat component in the composite meat. The RPA-LFA of the chicken and pig meat identification was successfully applied to processed meat products and to meat after heating. The results were confirmed by real-time PCR. Ultimately, the developed analysis is specific and enables the detection of pork and chicken impurities with high accuracy in raw and processed meat mixtures. The proposed rapid full-cycle technique could be adopted for the authentication of other meat products.

The Potential Use of Isothermal Amplification Assays for In-Field Diagnostics of Plant Pathogens.

Rapid, sensitive, and timely diagnostics are essential for protecting plants from pathogens. Commonly, PCR techniques are used in laboratories for highly sensitive detection of DNA/RNA from viral, viroid, bacterial, and fungal pathogens of plants. However, using PCR-based methods for in-field diagnostics is a challenge and sometimes nearly impossible. With the advent of isothermal amplification methods, which provide amplification of nucleic acids at a certain temperature and do not require thermocyclic equipment, going beyond the laboratory has become a reality for molecular diagnostics. The amplification stage ceases to be limited by time and instruments. Challenges to solve involve finding suitable approaches for rapid and user-friendly plant preparation and detection of amplicons after amplification. Here, we summarize approaches for in-field diagnostics of phytopathogens based on different types of isothermal amplification and discuss their advantages and disadvantages. In this review, we consider a combination of isothermal amplification methods with extraction and detection methods compatible with in-field phytodiagnostics. Molecular diagnostics in out-of-lab conditions are of particular importance for protecting against viral, bacterial, and fungal phytopathogens in order to quickly prevent and control the spread of disease. We believe that the development of rapid, sensitive, and equipment-free nucleic acid detection methods is the future of phytodiagnostics, and its benefits are already visible.

Recombinase Polymerase Amplification Assay with and without Nuclease-Dependent-Labeled Oligonucleotide Probe.

The combination of recombinase polymerase amplification (RPA) and lateral flow test (LFT) is a strong diagnostic tool for rapid pathogen detection in resource-limited conditions. Here, we compared two methods generating labeled RPA amplicons following their detection by LFT: (1) the basic one with primers modified with different tags at the terminals and (2) the nuclease-dependent one with the primers and labeled oligonucleotide probe for nuclease digestion that was recommended for the high specificity of the assay. Using both methods, we developed an RPA-LFT assay for the detection of worldwide distributed phytopathogen-alfalfa mosaic virus (AMV). A forward primer modified with fluorescein and a reverse primer with biotin and fluorescein-labeled oligonucleotide probe were designed and verified by RPA. Both labeling approaches and their related assays were characterized using the in vitro-transcribed mRNA of AMV and reverse transcription reaction. The results demonstrated that the RPA-LFT assay based on primers-labeling detected 103 copies of RNA in reaction during 30 min and had a half-maximal binding concentration 22 times lower than probe-dependent RPA-LFT. The developed RPA-LFT was successfully applied for the detection of AMV-infected plants. The results can be the main reason for choosing simple labeling with primers for RPA-LFT for the detection of other pathogens.

The Challenge for Rapid Detection of High-Structured Circular RNA: Assay of Potato Spindle Tuber Viroid Based on Recombinase Polymerase Amplification and Lateral Flow Tests.

An assay was developed to detect the potato spindle tuber viroid (PSTVd), a dangerous plant pathogen that causes crop damage resulting in economic losses in the potato agriculture sector. The assay was based on the reverse transcription and recombinase polymerase amplification (RT-RPA) of PSTVd RNA coupled with amplicon detection via lateral flow assay (LFA). Primers labeled with fluorescein and biotin were designed for RT-RPA for effective recognition of the loop regions in the high-structured circular RNA of PSTVd. The labeled DNA amplicon was detected using lateral flow test strips consisting of a conjugate of gold nanoparticles with antibodies specific to fluorescein and streptavidin in the test zone. The RT-RPA-LFA detected 106 copies of in vitro transcribed PSTVd RNA in reaction or up to 1:107 diluted extracts of infected plant leaves. The assay took 30 min, including the RT-RPA stage and the LFA stage. The testing of healthy and infected potato samples showed full concordance between the developed RT-RPA-LFA and quantitative reverse transcription polymerase chain reaction (RT-qPCR) and the commercial kit. The obtained results proved the feasibility of using the developed assay to detect PSTVd from a natural source.

Development of lateral flow assay combined with recombinase polymerase amplification for highly sensitive detection of Dickeya solani.

Dickeya solani, one of the most significant bacterial pathogens, infects potato plants, resulting in severe economic damage. In this study, a lateral flow assay (LFA) combined with isothermal DNA amplification was developed for rapid, specific, and sensitive diagnosis of the potato blackleg disease caused by D. solani. Recombinase polymerase amplification (RPA) was chosen for this purpose. Five primer pairs specific to different regions of the D. solani genome were designed and screened. A primer pair providing correct recognition of the target sequence was aligned with the SOL-C region specific to D. solani and flanked by fluorescein (forward primer) and biotin (reverse primer). Lateral flow test strips were constructed to detect DNA amplicons. The RPA-LFA demonstrated a detection limit equal to 14,000 D. solani colony-forming units per gram of potato tuber. This assay provided sensitivity corresponding to the polymerase chain reaction (PCR) but was implemented at a fixed temperature (39 °C) over 30 min. No unspecific reactions with Pectobacterium, Clavibacter, and other Dickeya species were observed. Detection of latent infection of D. solani in the potato tubers by the developed RPA-LFA was verified by PCR. The obtained results confirmed that RPA-LFA has great potential for highly sensitive detection of latent infection.

Nucleic acid lateral flow assay with recombinase polymerase amplification: Solutions for highly sensitive detection of RNA virus.

We propose nucleic acid lateral flow assay (LFA) coupled with reverse transcription recombinase polymerase amplification (RT-RPA) resulting from step-by-step multiparametric adjustments to both RT-RPA reactions and LFA interactions. The assay was realized for RNA virus detection using the example of potato virus X (PVX), a dangerous phytopathogen. The assay stages were adjusted for sensitive detection. (1) DNA target was designed and verified. A fragment (146 bp) of coat protein gene (gp5) and biotin-/fluorescein-labeled forward/reverse primers were chosen to produce target amplicons. (2) In a test strip, the construction advantage of the realization of the highest affinity interaction (biotin-streptavidin in our research) through gold nanoparticle conjugate (streptavidin immobilized on the GNP surface) was demonstrated. (3) RPA with reverse transcription was adjusted including primer concentration, order of components' mixing, and reaction temperature. Due to the adjustments, the assay was able to detect 0.14 ng PVX per g potato leaves at 30 min. The PVX assay was 260 times more sensitive than conventional lateral flow assay based on antibodies and demonstrated the same sensitivity as PCR detection. The proposed adjustments are applicable for ultrasensitive and rapid detection of various RNA viruses.