Life in Darwin’s dust: intercontinental transport and survival of microbes in the nineteenth century Anna A. Gorbushina, 1 Renate Kort, 1 Anette Schulte, 1 David Lazarus, 2 Bernhard Schnetger, 3 Hans-Jürgen Brumsack, 3 William J. Broughton 4 * and Jocelyne Favet 4 1 Geomicrobiology, ICBM, Carl von Ossietzky Universität, Oldenburg, Carl-von-Ossietzky Str. 9-11, 26111 Oldenburg, Germany. 2 Museum für Naturkunde, Humboldt Universität zu Berlin, Invalidenstrasse 43, 10115 Berlin, Germany. 3 Microbiogeochemistry, ICBM, Carl von Ossietzky Universität, Oldenburg, Carl-von-Ossietzky str. 9-11, 26111 Oldenburg, Germany. 4 LBMPS, Université de Genève, 30 quai Ernest-Ansermet, 1211 Genève 4, Switzerland. Summary Charles Darwin, like others before him, collected aeolian dust over the Atlantic Ocean and sent it to Christian Gottfried Ehrenberg in Berlin. Ehrenberg’s collection is now housed in the Museum of Natural History and contains specimens that were gathered at the onset of the Industrial Revolution. Geochemical analyses of this resource indicated that dust col- lected over the Atlantic in 1838 originated from the Western Sahara, while molecular-microbiological methods demonstrated the presence of many viable microbes. Older samples sent to Ehrenberg from Barbados almost two centuries ago also contained numbers of cultivable bacteria and fungi. Many diverse ascomycetes, and eubacteria were found. Scanning electron microscopy and cultivation sug- gested that Bacillus megaterium, a common soil bac- terium, was attached to historic sand grains, and it was inoculated onto dry sand along with a non-spore- forming control, the Gram-negative soil bacterium Rhizobium sp. NGR234. On sand B. megaterium quickly developed spores, which survived for extended periods and even though the numbers of NGR234 steadily declined, they were still consider- able after months of incubation. Thus, microbes that adhere to Saharan dust can live for centuries and easily survive transport across the Atlantic. Introduction Although ancient mariners experienced intercontinental dust storms that blew west-wards across the Atlantic Ocean from Africa (see Ehrenberg, 1849; Husar, 2004), one of the first scientific observations of these phenom- ena was presented by Charles Darwin (1845) who wrote ‘On the 16th of January, 1832, we anchored at Porto Praya, in St. Jago, the chief island of the Cape de Verd archipelago. Generally the atmosphere is hazy; and this is caused by the falling of impalpably fine dust, which was found to have slightly injured the astronomical instruments. The morning before we anchored at Porto Praya, I collected a little packet of this brown-coloured fine dust, which appeared to have been filtered from the wind by the gauze of the vane at the masthead. Mr Lyell 1 has also given me four packets of dust which fell on a vessel a few hundred miles northward of these islands’. These samples were passed on to Christian Gottfried Ehren- berg, a pioneer of aerobiology (Krumbein, 1995) at the Royal Prussian Academy of Sciences in Berlin. Darwin further wrote that ‘In five little packets which I sent him he (Professor Ehrenberg) has ascertained no less than 67 different organic forms’ (Ehrenberg, 1845; Darwin, 1846). Shortly before Ehrenberg’s death in 1876, this collection was donated to the Prussian Academy and it is currently housed in the Museum für Naturkunde der Humboldt- Universität Berlin (Lazarus, 1998; Lazarus and Jahn, 1998). Dust that originates from deserts is now known to be a vehicle for the spread of microbial communities via natural atmospheric pathways (Griffin et al., 2002; 2006; Kellog et al., 2004; Weir-Brush et al., 2004; Prospero et al., 2005). Early in the 21st century, scientific curiosity about what dust storms may carry has been supplemented with worries about accidental or intentional spread of contami- nants and diseases (Brown and Hovmoller, 2002). As Ehrenberg’s collection provides snapshots of a more Received 13 July, 2007; accepted 6 September, 2007. *For correspondence. E-mail william.broughton@bioveg.unige.ch; Tel. (+41) 22 3793 108/9; Fax (+41) 22 3793 009. 1 ‘I must take this opportunity of acknowledging the great kindness with which this illustrious naturalist has examined many of my specimens. I have sent (June, 1845) a full account of the falling of this dust to the Geological Society’ (Darwin, 1846). Environmental Microbiology (2007) 9(12), 2911–2922 doi:10.1111/j.1462-2920.2007.01461.x © 2007 The Authors Journal compilation © 2007 Society for Applied Microbiology and Blackwell Publishing Ltd