Biology subjects

Sima, R.

Publications and source records attributed to Sima, R..

3 recordsLinked to original sources

bioRxiv2025

Directed Evolution of a Pantoea Strain for Antibiotic Production via Interspecies Competition: A Reproducible Experimental Approach

A novel methodology for evolving antibiotic-producing bacterial strains is presented, based on interspecies competition and environmental pressure. Using a previously undescribed strain of the genus Pantoea, we established a breeding protocol in which gradual exposure to different bacterial pathogens at increasing temperatures resulted in the selective emergence of antibiotic-producing variants. The target pathogens included Staphylococcus aureus, Acinetobacter baumannii, Streptococcus agalactiae, Escherichia coli, and Pseudomonas aeruginosa. The competitive passages were performed over a range of temperatures, gradually selecting for strains capable of inhibiting these species. Antibiotic activity was confirmed via disk diffusion assays. Although the chemical identity of the active compounds remains to be determined, their biological effects are reproducible and strain-specific. The approach provides a low-cost, scalable method for the generation of new antibiotic-producing bacterial strains.

microbiology↗

bioRxiv2024

Elevated developmental temperatures below the lethal limit reduce Aedes aegypti fertility

Aedes aegypti mosquitoes are the principal vectors of dengue and continue to pose a threat to human health, with ongoing urbanization, climate change, and trade all impacting the distribution and abundance of this species. Hot periods are becoming increasingly common and their impacts on insect mortality have been well established, but they may have even greater impacts on insect fertility. In this study, we investigated the impacts of high temperatures on Ae. aegypti fertility both within and across generations. Mosquitoes developing under elevated temperatures exhibited higher critical thermal maxima (CTmax) reflecting developmental acclimation, but their fertility declined with increasing developmental temperature. In females, elevated developmental temperatures decreased fecundity while in males it tended to decrease egg hatch proportions and the proportion of individuals producing viable offspring. Rearing both sexes at 35{degrees}C increased fecundity in the subsequent generation but effects of elevated temperatures persisted across gonotrophic cycles within the same generation. Moreover, exposure of adults to 35{degrees}C further decreased fertility beyond the effects of developmental temperature alone. These findings highlight sub-lethal impacts of elevated temperatures on Ae. aegypti fertility and plastic responses to thermal stress within and across generations. This has significant implications for mosquito populations thriving in increasingly warmer environments.

ecology↗

bioRxiv2018

Tracking Borrelia afzelii from infected Ixodes ricinus nymphs to mice suggests a direct ‘gut-to-mouth’ route of Lyme disease transmission

Quantitative tracking of Borrelia afzelii has shown that its transmission cycle differs from the salivary route of B. burgdorferi transmission by Ixodes scapularis. Borrelia afzelii are abundant in the guts of unfed Ixodes ricinus nymphs and their numbers continuously decrease during feeding. In contrast, spirochetes are not present in the salivary glands. Borrelia afzelii transmission starts during the early stages of feeding, spirochetes could be detected in murine skin within 1 day of tick attachment. Tick saliva is not essential for B. afzelii infectivity, the main requirement for successful host colonization being a change in outer surface protein expression that occurs in the tick gut during feeding. Spirochetes in vertebrate mode are able to survive within the host even if the tick is not present. On the basis of our data we propose that a direct gut-to-mouth route of infection appears to be the main route of B. afzelii transmission.\n\nImportanceLyme borreliosis is the most common vector-borne disease in the USA and Europe. The disease is caused by the Borrelia spirochetes and is transmitted through Ixodes ticks. A better understanding of how Borrelia spirochetes are transmitted is crucial for development of efficient vaccines for preventing Lyme borreliosis. Here we present that the transmission of European B. afzelii spirochetes by I. ricinus ticks significantly differs from the model transmission cycle described for American B. burgdorferi/I. scapularis. We suggest that B. afzelii is not transmitted via salivary glands but most likely through the midgut to mouthpart route. We further demonstrate that tick saliva is not important for B. afzelii transmission and infectivity. Therefore, we support early studies by Willy Burgdorfer, who proposed that Borrelia transmission occurs by regurgitation of infected gut contents. Our findings collectively point to the Borrelia-tick midgut interface as the correct target in our endeavours to combat Lyme borreliosis.

microbiology↗