Microorganisms (microbes) thrive everywhere on planet Earth as long as there are opportunities
for exchanging Redox energy with the environment and for the harvest of nutrients
including life's central element, carbon. The use of the term “Microbe” has changed
with time and while it described at one point all living things not visible with the
naked eye, the status quo of science today justifies its usage mainly to part “genetically
programmed entities” from animals and plants. This would allow also the inclusion
of viruses as they are such entities albeit not living organisms that can escape from
host cells without losing their genetic program. We know now that their evolution
is intimately connected to the evolution of cellular beings (Koonin, 2009 and references
therein).
After Linneus, Haeckel, Cohn, Orla-Jensen, Chatton, Whittaker, Stanier and Doudoroff,
research by Carl Woese and colleagues beginning in the 1970s pioneered a new understanding
of relationships between all cellular organisms (Woese and Fox, 1977; Woese et al.,
1990), which provided a scientific basis for a natural classification of the “unseen
majority of life” (Whitman et al., 1998; Ward, 2002; Heijden et al., 2008) and contributed
greatly to our present understanding of the origin of life (Koonin and Martin, 2005;
Russell, 2007; Wachtershauser, 2007; Forterre, 2008; Glansdorff et al., 2008; Lane
et al., 2010). Much of this insight was possible from the realization that the becoming
of Earth and life are intricately intertwined, that microbial life was the sole occupant
for over half of Earth's existence and that microbial life is likely plentiful in
the Universe. To tie all this together required new thinking in the “ligand sphere”
(Wachtershauser, 1994; Martin and Russell, 2003) as well as a revolution in experimental
methodology such as dideoxy-primer sequencing and PCR. Both methods were sparked by
the brilliant concept of primer extension developed by Ray Wu (Wu, 1970; Wu and Taylor,
1971), whose applications provided later for molecular (microbial) ecology and the
key to open the door to the ∼omics age thereby paving the way for the present biodiversity
initiative and hot new areas in the biological sciences such as Phylogenomics and
Systems MicroBiology.
While phototrophy was conceptually easily accessible to scientists’ and laypersons’
thinking, the discovery of lithotrophy (“chemosynthesis”) by the great Sergei Winogradsky
(1887, 1890) still before the turn to the 20th century finally allowed for a biochemical
and physiological explanation of light-less primary production, observed as a phenomenon
over centuries by a large number ecologists and physiologists. Finally, Kluyver (1924)
together with his colleague Hendrick Donker (Kluyver and Donker, 1926) proposed their
far-reaching hypothesis on the unity (universality) of synthesis, then the trailblazer
for Cornelius van Niel's concept of a “General Microbiology” and today one of the
last standing paradigms in biology. Now, more than a century later, we know that microorganisms
are “the greatest chemists” on our planet capable of exploiting every chemical reaction
that is thermodynamically feasible to sustain themselves and proliferate, whether
with or without light. This metabolic wizardry enabling the facilitation of global
biogeochemical cycles – supported by large scale recycling via plate tectonics – is
the basis of all life as we know it. It is currently estimated that the global microbial
network consists of more than 1030 Bacteria and Archea, many of which are infected
by a large cohort of the estimated total count of 1031 viruses. Add to it the estimate
for the biodiversity of organisms in the Kingdom Fungi, of which only about 5% of
the estimated 1.5 million species has been formally classified, and the plot is thickening.
Koch's (1876) first scientific implication of a bacterium as the causal agent of disease
in an animal and Burrill's (1878) identification of a bacterium as the cause of plant
disease were followed by numerous etiological reports that implicated bacteria (i.e.,
Kitasato, Klebs, Koch, Loeffler, Neisser, Pasteur, Pfeiffer, Roux, Smith and Kilbourne,
Welch and Nuttall, and Yersin), parasites (Lewis, 1878), fungi (Ophuls and Moffitt,
1900) and viruses (Ivanowski, 1892; Reed et al., 1900) as the causal agents of disease,
paired with research on how to protect healthy and infected hosts from (re)exposure,
which also started the race for the cure (Pasteur, Ehrlich, Metchnikoff) and, eventually,
research (Ehrlich, Kitasato, von Behring) that nurtured hope for finding a “silver
bullet.” This time was also the beginning of research that paved the way for the purposeful
use of microbes to the benefit of mankind such as the souring of milk (Lister, 1878)
in today's dairy industry and the use of nitrification (Schloesing and Muntz, 1877)
for sewage treatment and bioremediation.
Like all of our science colleagues, microbiologists teach and train college students,
interact with the lay public and their reflection on the field is a welcome feedback
to not necessarily what we do and know but how we succeed in communicating it understandably
to those who stand outside. It is often disheartening to hear how little interest
all of microbiology but the work on causal agents of human disease (and their defeat)
command. I usually escape the frustration by posing the following question: “Imagine
that we found the therapies to cure all cancers and genetic failures and can combat
every infectious disease directly or indirectly (i.e., by contaminated food) caused
by bacteria, fungi, viruses and parasites. Do you think that would allow mankind to
thrive and prosper?” I then answer the usually predictable “yes” response by the audience
with the following challenge: “So what if we run out of potable water?” This usually
ends in complete amazement … and it is then when the crowd understands that planet
Earth is maintained and owned by the microbes and that it is in our very best interest
to know “Who is there?” and “What is everybody doing?” Finding the answers to these
questions needs an interdisciplinary effort of microbial ecologists, bio(geo)chemists,
(eco)physiologists, geneticists, systems microbiologists, biotechnologists, modelers
and theoretical biologists. The last decade has, for instance, changed our view on
many aspects of the microbial biogeochemical cycles including the already heavily
impacted global nitrogen cycle (Rockstrom et al., 2009), which is mainly due to tremendous
advances in methods, techniques and approaches. Many novel processes and the molecular
inventory and microbes that facilitate them have been discovered only within the last
5–10 years and the process is in progress. This was also possible because microbiologists
came finally to realize that pure culture microbiology – although instrumental for
the dissection of cells and the study of how their inner circuits work as well as
for the implication of a causal agent in disease – does not reflect how microbes live
in their respective environmental niches: Microbes are social beings that live, communicate
and work together spatially and temporally embedded in complex communities, be it
in water or soil or in facultative or obligate associations with each other or with
macroorganismal hosts.
So as we are taking much better account of the unseen majority of life, unravel the
biogeochemical processes that microbes facilitate, thereby making planet Earth habitable
for all forms of life; as we increasingly identify the rules by which microorganisms
interact with co-evolving viruses and “macroorganisms” in health and disease; and
as we find more and better strategies to mitigate the detrimental effects of anthropogenic
activities on the abundance, diversity, distribution and activity of microbial communities,
the grand challenge of Microbiology today is to know better, protect, utilize and
celebrate the unseen majority on our planet.
Frontiers in Microbiology with its family of Specialty Journals will be the 21st century
approach to communicate all this progress to both the specialist and a wider audience
of readers in the field.