Helvécio M. Santos Júnior

Bio: Helvécio M. Santos Júnior is an academic researcher from Universidade Federal de Lavras. The author has contributed to research in topics: Root-knot nematode & Exigua. The author has an hindex of 8, co-authored 10 publications receiving 156 citations. Previous affiliations of Helvécio M. Santos Júnior include Federal University of Rio de Janeiro.

Evaluation of native and exotic Brazilian plants for anticancer activity

Abstract: Native and exotic Brazilian plants collected in the State of Minas Gerais were evaluated for their anticancer potential. Methanol extracts from leaves of 51 plant species were tested for cytotoxicity against four tumor cell lines: B16 (murine skin), HL-60 (human leukemia), MCF-7 (human breast), and HCT-8 (human colon). Plant extracts that exhibited IC50 values less than 30 μg/ml against any tumor cell line were tested on sea urchin egg development and mouse erythrocytes. In addition, all extracts were evaluated for their general toxicity using the brine shrimp lethality assay. The most active extracts against the tumor cells were those obtained from Lantana fucata, Copaifera langsdorffii, and Momordica charantia. These three extracts inhibited sea urchin development from the first cleavage, but those from C. langsdorffii and M. charantia were very active against mouse erythrocytes. Only the L. fucata extract presented no hemolytic activity. Consequently, although the extracts of L. fucata, M. charantia, and C. langsdorffii could be useful in the development of new anticancer products, the first of these extracts is the most promising since it did not present unspecific toxicity, as suggested by negative results obtained with brine shrimp lethality and mouse erythrocytes assays.

Purification and identification of metabolites produced by Bacillus cereus and B. subtilis active against Meloidogyne exigua, and their in silico interaction with a putative phosphoribosyltransferase from M. incognita

Abstract: Com o objetivo de contribuir para o desenvolvimento de produtos para o controle de Meloidogyne exigua, as bacterias Bacillus cereus e B. subtilis foram cultivadas em meio liquido de cultura para produzirem metabolitos ativos contra este nematoide parasita de plantas. Os fracionamentos dos extratos em diclorometano dos meios de cultura produziram uracila, 9H-purina e di-idrouracila. Todos os compostos foram ativos contra M. exigua, sendo o ultimo o mais eficiente. Ele apresentou CL50 de 204 µg/mL contra o nematoide, enquanto uma CL50 de 260 µg/mL foi observada para o nematicida comercial carbofuran. Uma busca por complexos proteina-ligante nos quais o ligante fosse estruturalmente similar a di-idrouracila resultou na selecao de fosforibosiltransferases, cujas sequencias foram utilizadas em uma busca in silico no genoma de M. incognita por sequencia de aminoacidos semelhante. A sequencia resultante foi modelada e di-idrouracila e 9H-purina foram inseridos nos sitios ativos desta provavel fosforibosiltransferase, resultando em complexos proteina-ligante que foram submetidos a simulacoes por dinâmica molecular. Calculos das energias livres de ligacao destes complexos revelaram que a constante de dissociacao de di-idrouracila e 9H-purina da enzima e da ordem de 8,3 x 10-7 e 1,6 x 10-6 M, respectivamente. Consequentemente, estas substâncias e a provavel fosforibosiltransferase podem ser de grande utilidade para o desenvolvimento de novos produtos para o controle de M. exigua.

The activity of amino acids produced by Paenibacillus macerans and from commercial sources against the root-knot nematode Meloidogyne exigua

Abstract: The rhizobacterium Paenibacillus macerans was grown in tryptic soy broth and after separating the cells by centrifugation the activity of fractions of the supernatant was tested against Meloidogyne exigua juveniles. From HPLC analyses and spectral data, the most active fractions were found to contain alanine, glutamic acid, glycine, histidine, threonine and valine, which were probably produced by bacterial hydrolysis of proteic nutrients. Amino acids from commercial sources were then assayed to confirm these results and to evaluate their potential for the control of nematodes. LC50 of 26 and 283 μg ml−1 were shown for the nematicide aldicarb and L-cysteine respectively when tested on M. exigua juveniles. At a concentration 38.4 times>LC50, the amino acid diminished the nematode population on coffee plants to values statistically equal to those obtained with aldicarb at a concentration 19.2 times>LC50.

Botanical Nematicides: A Review

Abstract: Despite the uselfuness of nematicidal compounds in agricultural practices, some serious concerns are raised today about their excessive use leading to enhancement of biodegradation mechanisms in soil expressed as lack of efficacy under field conditions and resistance development. Moreover, the phase-out of methyl bromide has led to the need for a valid alternative to organophosporous and carbamate compounds, such us fosthiazate, fenamiphos, oxamyl, and aldicarb. In the past years, intregated pest management strategies have been practised worldwide to maximize crop production while maintaining and contributing to agriculture sustainability. Biopesticides and specifically bionematicides constitute a desirable component of pest management technology and practices. Particularly, in the frame of our ongoing research on natural nematicides of botanical origin, we have reviewed the international bibliography for candidate nematicidal compounds. We report herein the nematicidal activity of plant metabolites on the basis of their chemical characteristics and structure.

Selected-fit versus induced-fit protein binding: Kinetic differences and mutational analysis

Abstract: The binding of a ligand molecule to a protein is often accompanied by conformational changes of the protein. A central question is whether the ligand induces the conformational change (induced-fit), or rather selects and stabilizes a complementary conformation from a pre-existing equilibrium of ground and excited states of the protein (selected-fit). We consider here the binding kinetics in a simple four-state model of ligand-protein binding. In this model, the protein has two conformations, which can both bind the ligand. The first conformation is the ground state of the protein when the ligand is off, and the second conformation is the ground state when the ligand is bound. The induced-fit mechanism corresponds to ligand binding in the unbound ground state, and the selected-fit mechanism to ligand binding in the excited state. We find a simple, characteristic difference between the on- and off-rates in the two mechanisms if the conformational relaxation into the ground states is fast. In the case of selected-fit binding, the on-rate depends on the conformational equilibrium constant, while the off-rate is independent. In the case of induced-fit binding, in contrast, the off-rate depends on the conformational equilibrium, while the on-rate is independent. Whether a protein binds a ligand via selected-fit or induced-fit thus may be revealed by mutations far from the protein's binding pocket, or other "perturbations" that only affect the conformational equilibrium. In the case of selected-fit, such mutations will only change the on-rate, and in the case of induced-fit, only the off-rate.

Plant growth promoting rhizobacteria (PGPR): A potential alternative tool for nematodes bio-control

Abstract: The increasing demand of the agricultural produce can be attained by optimizing the productivity potential and by minimizing the losses caused by notorious plant-parasitic nematode of the crops. Chemical based nematode control is an effective strategy to combat this biotic stress, but inappropriate and inadequate application of synthetic pesticides has exerted an adverse effect on bio-flora, fauna and natural enemies. Due to the environmental and regulatory pressure, use of potential biocontrol agents is the most welcomed way for nematode management by the farming community. There is an emerging market for Plant growth promoting rhizobacteria (PGPR) mediated eco-friendly biopesticides for plant-parasitic nematode biocontrol. Moreover, PGPR strains can enhance the plant growth through the production of various plant growth promoting substances. Based on the fact stated above, the present review focused on PGPR based nematodes biocontrol strategies, the direct and indirect mechanism of PGPR for nematode biocontrol and future prospect of PGPR based biocontrol agents against nematodes are discussed.