43 research outputs found
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Increases in ‘Candidatus Liberibacter asiaticus’ viability and investigations of biofilm-like structures in citrus juice medium
Huanglongbing disease of citrus, associated with infection by the bacterium ‘Candidatus Liberibacter asiaticus’ (LAS), has spread rapidly in the US since 2005. Attempts to culture LAS in vitro have not yielded a consistently reproducible culture method; therefore, obtaining knowledge about the infection process is difficult. To determine conditions which sustain LAS viability, LAS inoculum obtained from seeds of fruit from infected pomelo trees (Citrus grandis ‘Mato Buntan’) was added to different media, and cell viability was monitored for several weeks using quantitative polymerase chain reaction (qPCR) in conjunction with ethidium monoazide (EMA). Among media tested, King’s B (K) did not support viability of LAS cells, while grapefruit juice (G) allowed LAS cells to survive in vitro for ~20 days. In media that sustained LAS viability, a reproducible biofilm-like substance was formed over time at the air-liquid interface of culture flasks and glass slides inserted in cultures. Fluorescence in situ hybridization (FISH) showed the biofilm contains aggregates of LAS cells, which was confirmed by qPCR. 16S rDNA libraries of the biofilm samples have been constructed and will be sequenced via Illumina next-generation sequencing to determine their bacterial composition. To elucidate why juice-based media prolongs LAS viability, the elemental nutrient compositions of the media and the biofilm were analyzed via inductively coupled plasma optical emission spectrometry (ICP-OES). Compositions were compared, and specific elements, such as potassium and calcium, were more abundant in media that sustain LAS cell viability. Results will contribute to future development of a culture medium for LAS
Ancestral transoceanic colonization and recent population reduction in a nonannual killifish from the Seychelles archipelago
Whether freshwater fish colonize remote islands following tectonic or transoceanic dispersal remains an evolutionary puzzle. Integrating dating of known tectonic events with phylogenomics and current species distribution, we find that killifish species distribution is not explained by species dispersal by tectonic drift only. Investigating the colonization of a nonannual killifish (golden panchax, Pachypanchax playfairii) on the Seychelle islands, we found genetic support for transoceanic dispersal and experimentally discovered an adaptation to complete tolerance to seawater. At the macroevolutionary scale, despite their long-lasting isolation, nonannual golden panchax show stronger genome-wide purifying selection than annual killifishes from continental Africa. However, progressive decline in effective population size over a more recent timescale has probably led to the segregation of slightly deleterious mutations across golden panchax populations, which represents a potential threat for species preservation in the long term