Single-cell mutation rate of turnip crinkle virus (-)-strand replication intermediates.

Viruses with single-stranded, positive-sense (+) RNA genomes incur high numbers of errors during replication, thereby creating diversified genome populations from which new, better adapted viral variants can emerge. However, a definitive error rate is known for a relatively few (+) RNA plant viruses, due to challenges to account for perturbations caused by natural selection and/or experimental set-ups. To address these challenges, we developed a new approach that exclusively profiled errors in the (-)-strand replication intermediates of turnip crinkle virus (TCV), in singly infected cells. A series of controls and safeguards were devised to ensure errors inherent to the experimental process were accounted for. This approach permitted the estimation of a TCV error rate of 8.47 X 10-5 substitution per nucleotide site per cell infection. Importantly, the characteristic error distribution pattern among the 50 copies of 2,363-base-pair cDNA fragments predicted that nearly all TCV (-) strands were products of one replication cycle per cell. Furthermore, some of the errors probably elevated error frequencies by lowering the fidelity of TCV RNA-dependent RNA polymerase, and/or permitting occasional re-replication of progeny genomes. In summary, by profiling errors in TCV (-)-strand intermediates incurred during replication in single cells, this study provided strong support for a stamping machine mode of replication employed by a (+) RNA virus.

Antimicrobial effect of bothropstoxin-i in broilers

Bacterial resistance is a sanitary issue explained by indiscriminate use of nonprescription drugs, and antimicrobial use in food production for growth promotion. Bothropstoxin-I (BthTx-I) is a phospholipase A2 (PLA2) from Bothrops jararacussu venom, which has a known antimicrobial effect. The goal of this study was the unprecedented evaluation of in vivo antimicrobial activity of BthTx-I in broilers. Microbiological, biochemical, and histological parameters were determined using 84 21-day old broilers that were kept in cages with four birds each at a density of 625 cm2/broiler. The experiment was randomized by three treatments with seven repetitions of four broilers each that lasted seven days. The treatments were: 1) bacitracin zinc diet; 2) PLA2-BthTx-I; 3) without additives. The data obtained from the studied variables was subjected to analysis of variance and an F-test at the 5% significance level. Averages of each variable in each treatment were compared by Tukey’s test. Broiler bacterial cloacal counts showed that BthTx-I decreased the microbial population without reducing body weight, intestinal morphology, or liver or kidney histopathological damage. The toxin showed in vivo activity, being an alternative for better performance in the production of broiler chickens, because it acted by decreasing the microbial load of potentially pathogenic bacteria in the intestinal microbiota of the birds and did not cause muscle, liver or kidney damage at the assessed dosage.