Microbial immigration across the Mediterranean via airborne dust.

Riccardo Rosselli,Pietro Cappuccinelli,Annalisa Canu,Andrea Squartini,Pierpaolo Duce,Maura Fiamma,Gabriella Pintus,Rosella Muresu,Massimo Deligios,Grazia Pellizzaro

doi:10.1038/srep16306

Abstract

Dust particles lifting and discharge from Africa to Europe is a recurring phenomenon linked to air circulation conditions. The possibility that microorganisms are conveyed across distances entails important consequences in terms of biosafety and pathogens spread. Using culture independent DNA-based analyses via next generation sequencing of the 16 S genes from the airborne metagenome, the atmospheric microbial community was characterized and the hypothesis was tested that shifts in species diversity could be recorded in relation to dust discharge. As sampling ground the island of Sardinia was chosen, being an ideal cornerstone within the Mediterranean and a crossroad of wind circulation amidst Europe and Africa. Samples were collected in two opposite coastal sites and in two different weather conditions comparing dust-conveying winds from Africa with a control situation with winds from Europe. A major conserved core microbiome was evidenced but increases in species richness and presence of specific taxa were nevertheless observed in relation to each wind regime. Taxa which can feature strains with clinical implications were also detected. The approach is reported as a recommended model monitoring procedure for early warning alerts in frameworks of biosafety against natural spread of clinical microbiota across countries as well as to prevent bacteriological warfare.

Highlights

The atmosphere-dispersed particulate matter, constituted by a mixture of particles, containing variable fractions of natural solids and pollutants[19,20,21], represents a carrier able to passively convey an array of different microorganisms
On the subsequent period from February 20th, the above circulation regime halted, high pressure cells over Europe caused opposite winds blowing from northeastern origin, which passed over Italy and Sardinia and allowed to collect samples representing the dust-free control conditions
The first intrusion of African air masses occurred on the 15th-17th, mainly affecting the PM10 levels in the north of Sardinia

Summary

Introduction

The atmosphere-dispersed particulate matter, constituted by a mixture of particles, containing variable fractions of natural solids and pollutants[19,20,21], represents a carrier able to passively convey an array of different microorganisms. Authors at USGS using DNA sequencing of the ribosomal gene, were able to isolate and identify over 200 viable bacteria and fungi in samples from St. John in the U.S Virgin Islands in 2000 during dust air-driven particle transport events[23]. The association between microorganisms and air pollutants like PM2.5 and PM10 (particulate matter with diameters less than 2.5 and 10 μ m, respectively)[30] could represent a recently evolved transfer-mechanism supporting and increasing their natural dust-mediated dispersion and opening new ways for their epidemic diffusion. Dust transported by winds can reach an elevation up to 8 km in the atmosphere over the Mediterranean basin[33]

Methods

Results

Conclusion