Think big: Global challenges

As the world becomes more global, we are becoming more aware that a large number of issues affect entire areas of the planet, with, next to climate change, the issue of global pollution by industrial waste and toxic chemicals. Pollutants produced at a given site are frequently mobilised to the upper layers of atmosphere and then deposited in remote areas, sometimes at high concentrations (Kallenborn, 2006; Daly and Wania, 2005). Unfortunately, it appears that nowhere in the world qualifies properly as a pristine, chemically virgin area. In this respect, it is worth noting that many antibiotics and other pharmaceuticals are eligible as authentic pollutants as well. In reality, there is not a sharp divide between synthetic molecules with antimicrobial activity and the many recalcitrant compounds produced or mobilised by the chemical industry (Alonso et al., 1999, 2001; Martinez et al., 2009). In other cases, xenobiotic compounds or their degradation intermediates become endocrine disrupters with devastating consequences for entire ecosystems. Finally, a set of convergent circumstances, i.e. changes in weather, global dissemination of microbial vectors through expanding transport networks and rapid evolution of antibiotic resistance, have led to the reappearance of epidemic diseases as well as the emergence of new ones. One daunting example of this regards the clear environmental origin of cholera outbreaks, which accounts for the sporadic and erratic occurrence of epidemics of this disease (Colwell, 1996; Colwell et al., 1998).

A better understanding of the connections between man-induced environmental changes and infectious diseases is desperately required. Such information is needed not only for explaining events in retrospect, but also for anticipating outbreaks and informing preventive measures. In summary, climatic change, pollution and infectious processes are at the top of the many issues that must be faced at a global scale. Is there any contribution of the genetic reservoir of microbial diversity for addressing these phenomenal problems?

The history of the planet Earth records a considerable number of changes in the composition of the atmosphere that can be traced to microbial action. One of them occurred 2 to 3 billion years ago, when primitive microbes acquired the ability to generate O2 out of water using the energy from sunlight. This event altered altogether the ecology of Earth, as organisms were forced to cope with oxidative damage or else faced extinction. This change created new niches and heralded the emergence of the multi-cellular life forms during the Cambrian explosion (approximately 540 million years ago). Since then, the fossil record provides evidence of not less than five mass extinctions. Some of them have been attributed to a sudden change in the global composition of the atmosphere brought about by production of hydrogen sulphide by bacteria that lived in stagnant, deoxygenated water (Grice et al., 2005; Huey and Ward, 2005). Micro-organisms not only sense and reflect global environmental change, but they also contribute actively to bring it about. On this basis, only the global microbiota (which contributes the largest share of the Earth’s biomass) has the high-scale catalytic power that would be required to decrease the ramping CO₂ levels, counteract the global warming and neutralise harmful emissions.

Our level of understanding of these processes is not enough yet as to be able to exploit them in our favour, so much more research is still required to this end. One ongoing (and timid) example of the use marine microbes for increasing CO₂ deposition involves the introduction of iron particles in the nutrient-rich, but iron-deficient, ocean waters in order to stimulate the growth of phytoplankton blooms (Pollard et al., 2009). A growing number of marine scientists (as well as businesses) are exploring such fertilisation as a way to foster the onset of plankton populations and sequester large amounts of CO₂ for reducing global warming and preventing ocean acidification. The approach is, however, not devoid of problems (Kintisch, 2008; Tollefson, 2008). When the organic material produced by a plankton bloom sinks to deeper waters, the resulting decomposition may use up oxygen in the medium and cause a destructive effect on marine life. Another concern is the effect of iron fertilisation on nutrients other than iron in the ocean, which may be depleted by phytoplankton growth. Yet, the iron fertilisation concept is not devoid of basis and will surely be applied intensively in the next few years, even at the risk of causing low-oxygen incidents and episodes of local anoxia (Kintisch, 2008; Tollefson, 2008). At the moment, little is known about how these procedures will affect marine food chains, which obviously know no borders. It is likely that the management and even deliberate stimulation of the catalytic capacity of marine microbes and soil bacteria at a planetary scale will be a serious matter of international politics in the not so distant future (Tollefson, 2008).