Spores as time capsules
In considering the question, What is the role of Bacillus
spores in the environment? a simple and obvious answer
immediately presents itself – to preserve and to propagate
the genetic information contained within the bacterium.
Based on the well-known practice of inducing sporulation
in the laboratory by nutrient limitation, it is generally
accepted that spore formation evolved as a mechanism
for both spatial and temporal escape from local conditions
unfavorable to rapid growth [4]. (The elaborate molecular
mechanisms underlying spore longevity and survival
in the environment have recently been reviewed extensively
[4 and references therein], and will not be
reconsidered here.) As a device for preserving and dispersing
genetic information in the environment, the spore
is an incredible success. Spores can be found in environmental
samples obtained from virtually all parts of both
the Earth’s surface and subsurface [4, 6]. Reports of the
recovery of spores from environmental samples ranging
in age from decades to hundreds of thousands of years are
common [4, 7], and the scientific world has recently been
treated to more controversial reports of spore longevity
spanning geologic time scales. In 1994 and 1995 there
appeared reports that viable Bacillusspp. spores had been
isolated from the gut of a bee fossilized in Dominican
amber for an astounding 25–40 million years [8, 9]. Even
this incredible age for a spore has been dwarfed by the report
in 2000 of the discovery of Bacillus species 2-9-3,
which was recovered from a brine inclusion within a 250
million-year-old salt crystal from the Permian Salado