Geographic partitioning or environmental selection: What governs the global distribution of bacterial communities inhabiting floral nectar?

Floral nectar harbors microbial communities which have significant impacts on its chemistry, volatiles, nutritional contents, and attractiveness for pollinators. Yet, fundamental knowledge regarding the structure and composition of nectar-associated microbiomes remains largely unknown. Especially elusive are the environmental factors and spatial effects that shape nectar-inhabiting microbial communities. The aim of this study was to explore and analyze the role of geographical and environmental factors affecting the composition and global distribution of floral nectar microbiota. We explored and compared the structure of bacterial communities inhabiting the floral nectar of the widely spread and invasive tobacco tree (Nicotiana glauca) in six continents: South and North America, Australia, Europe, Africa, and Asia, using 16S rRNA gene sequencing. Environmental abiotic data for each sampled plant was obtained from the Worldclim database and applied for inferring the effects of environmental conditions on bacterial community structure and diversity. Most abundant in the nectar were the Proteobacteria, Firmicutes, and Actinobacteria phyla, with Acinetobacter and Rosenbergiella (Proteobacteria) being the dominant bacterial genera that contributed most to the dissimilarities between sites. Acinetobacter and Rosenbergiella abundances were negatively correlated and significantly higher in the Mediterranean regions (Greece, Israel, and the Canary Islands) compared to Argentina and Australia. Temperature, site-elevation, rainfall, and density of vegetation were found to have significant effects on the structure and diversity of these bacterial communities in the nectar. Vegetation density was positively correlated with microbial diversity, while increased temperatures and elevation reduced the diversity and evenness of bacterial communities. Mantel's test showed that the similarity between the bacterial communities' composition significantly decreased as distances between them increased. We conclude that both geographical distance and local environmental abiotic conditions affect and shape the composition and diversity of nectar inhabiting bacterial communities.

Descripción de la microbiota bacteriana residente en el biosólido generado en la planta de tratamiento de aguas residuales San Fernando. Itagüí, Colombia / Description of bacterial microbiota in biosolids generated in the San Fernando wastewater treatment plant. Itagüí, Colombia

RESUMEN Objetivo Caracterizar la microbiota bacteriana presente en los biosólidos generados en una de las plantas de tratamiento de aguas residuales más grande de Colombia. Materiales y Métodos Se utilizó la plataforma de secuenciamiento 454 de la compañía Roche para secuenciar las regiones variables V1-V3 y V6-V9 del marcador molecular 16S rRNA y caracterizar la microbiota. Adicionalmente, se aplicaron estrategias filogenéticas para la identificación de especies bacterianas de importancia. Resultados Nuestros análisis muestran que los Phyla más abundantes son Chloro-flexi, Proteobacteria, Bacteroidetes, Actinobacteria y Firmicutes. Los géneros clasificados más abundantes fueron Pseudomonas, Dysgonomonas y Proteiniphilum. Sin embargo, el grupo dominante según la región variable V1-V3 es una Anaerolineaceae que no se ajusta a las especies descritas para esta familia. Conclusiones En las muestras de biosólido analizadas predominan bacterias ambientales que participan en los procesos de estabilización de la materia orgánica durante los tratamientos biológicos de tipo secundario y la digestión anaerobia. Se detectaron secuencias de especies dentro de la familia Anaerolineaceae, los análisis filogenéticos muestran que probablemente se trata de especies no descritas. En el momento del estudio, se encontró que en el sistema de digestión anaerobia se genera biosolido con una baja carga de bacterias potencialmente patógenas.(AU)

ABSTRACT Objective To describe bacterial microbiota in the biosolids generated in one of the largest wastewater treatment plants of Colombia. Materials and Methods Using NGS technology, 16S rRNA Gene Amplicon libraries were amplified and sequenced. The Roche 454 FLX Titanium platform was used, while the V1-V3 and V6-V9 hypervariable regions were amplified and analyzed independently. Amplicon processing and bacterial classification were performed using the AmpliconNoise pipeline and the RDP Classifier tool. Results The analysis showed that the most dominant Phyla in the biosolids were Chlo-roflexi, Proteobacteria, Bacteroidetes, Actinobacteria and Firmicutes. The most dominant genera were Pseudomonas, Dysgonomonas and Proteiniphilum; however, the dominant group according in the V1-V3 variable region was Anaerolineaceae, which does not conform to the species described for this family. Pathogenic bacteria such as Salmonella and E. coli/Shigella were not detected in the studied biosolid sample. Conclusions In the biosolids samples analyzed, environmental bacteria involved in organic matter stabilization processes during secondary biological treatments and anaerobic digestion were predominant. One of the dominant species in this sludge is a novel species of the Anaerolineaceae group. At the time of the study, it was found that the anaerobic digester system was able to maintain pathogenic bacteria at very low concentrations.(AU)