Nannobacteria: why is it so hard to show what they are?
August 1, 1997: Robert Folk's article on nannobacteria (1) is very interesting. As a nonspecialist, however, I find it surprising that a question of this potential importance is still unresolved. The discovery of a new form of life previously thought impossible would surely be worthy of a Nobel prize. Why is it so hard to determine whether nannobacteria are of biological origin? Both the DNA and protein coat of viruses have been characterized, and viruses are smaller than nannobacteria.
To isolate nannobacteria it would seem sufficient to use a filter that would allow nannobacteria to pass, but not normal-sized bacteria. One could then apply the type of life detection tests used on the Viking missions.
In his review of Dr. Folk’s paper, Ralph Harvey's argument (2) that the size of the supposed nannobacteria would not allow them to contain RNA and a cell wall seems misleading. Virus particles, which are smaller than nannobacteria, are known to contain RNA and have a protein coat to maintain integrity. And perhaps like viruses, nannobacteria are unable to survive on their own, but need another organism to reproduce.
Finally, there are known bacteria that fall almost within the same size range as nannobacteria. These are the mycoplasmas which cause the most familiar form of pneumonia. The Britannica Online lists their size as 0.3 microns and there is probably some variation in size extending the range below 0.3 microns.
Current studies concerning nannobacteria
Despite the skepticism of some scientists, the existence of nanoorganisms is currently under intensive study. For example, in the current volume of Lunar and Planetary Science, a group including scientists from Lockheed Martin Engineering and Sciences, the NASA Johnson Space Center and the University of Houston discuss their ongoing work with samples of travertine from the Le Zitelle hotspring in Italy (3). This is the same material in which Folk first observed nannobacteria (4). Although careful to note that “no investigator has yet demonstrated whether (these spheroids, i.e., nannobacteria) are living bacteria, fossils, spores or abiotic precipitates” they say that their aim is to: (a) prepare spheroids in Le Zitelle travertine for transmission electron microscopy (TEM) combined with crystallographic and elemental analysis; (b) culture bacteria from the travertines using conditions and media specific to thermal spring samples; and (c) isolate and sequence DNA from the putative nannobacteria and compare it with DNA of known bacteria.
Another study reported in the current volume of Lunar and Planetary Science, examined basalts from the Columbia River Basin obtained at depths of several hundred meters (5). The authors incubated basalt samples in contact with anaerobic Columbia River Basin groundwater and its entrained bacteria for two years. They then examined the samples by scanning electron microscopy and observed what they describe as nano-scale coccoid (spheroidal) bacteria and intertwined tubes 20-30 nm wide and up to several microns in length. The authors suggest that these forms, which were absent from control (i.e., unincubated) basalt samples, are either nanobacteria or appendages of bacteria.
Vasconcelos and McKenzie, at the ETH-Zentrum, in Zurich, Switzerland, have studied dolomite (CaCO3.MgCO3) formation in a shallow-water coastal lagoon on the Brazilian coast (6). They found that dolomite deposition and sulfate reduction occurred when black (organic) sludge from the lagoon was incubated for 1 year at 4 oC under anoxic hypersaline conditions. Neither sulfate reduction nor dolomite deposition occurred when sterile samples were incubated under the same conditions. Examination of the deposits revealed subspherical nano-scale bodies that the authors refer to as nanobacteria and which they conclude are the active agents responsible for mineral deposition. The energy metabolism of these putative nanobacteria is given by the equation