Microbes and Plants - Freshwater Ecology: Concepts and Environmental Applications - page 129

et al., 1998). They are in every habitat and dominate flows of energy and
nutrients through aquatic ecosystems. The Bacteria are the most metabol-
ically diverse group of organisms on Earth. These unicellular organisms in-
clude heterotrophs that obtain energy from oxidizing organic carbon, pre-
dation, parasitism, chemoautotrophy, and photoautotrophy. Some of the
most crucial biogeochemical fluxes mediated by these organisms will be
discussed in Chapters 11-13). In addition, some of the most important hu-
man pathogens regularly transmitted by water are bacterial (Table 8.1),
and bacteria may be pathogens to many aquatic plants and animals. The
human pathogens are not restricted solely to developing countries. Out-
breaks of waterborne illness occur in parts of the world with a high stan-
dard of living (Young, 1996). Finally, bacteria are most often involved in
bioremediation using organisms to clean up pollution (see Chapter 14).
The methods used to determine bacterial groups are often based on
morphology or simple metabolic characteristics and likely do not accu-
rately represent evolutionary relationships among all bacteria. A common
identification scheme is presented in Bergey's Manual of Determinative
Bacteriology (Holt et al., 1994). Differentiation among bacterial species or
strains is based on reaction to staining compounds, morphology, motility,
production of extracellular materials, color, and metabolic capabilities.
Metabolic capabilities have the greatest util-
ity because the other attributes vary little
among species. Most bacteria are only 1 or
2

viruses could travel even greater distances in
aquifers with rapid water velocity, such as
karst systems or alluvium with coarse cobbles
(Sinton et al., 1997). For example, poliovirus
was demonstrated to move at least 20 m in a
cobble aquifer with less than 1% virus mortal-
ity (Deborde et al., 1999).
Factors that influence the movement of
viruses into and through groundwater include
the rate of water flow through the sediment, the
retentive properties of the sediments, and the
survival time of the virus. Factors that lower vi-
ral survival times in sediments include high tem-
peratures, microbial activity, drying, lack of ag-
gregation with other particles, and low organic
matter. Inactivation of viruses can be very rapid,
but poliovirus can remain active for up to 416
days in sandy soils (Sobsey and Shields, 1987).
Understanding the hydrology of soils and
sediments is necessary to assess the prob-
lems that may be related to sewage contami-
nation of groundwaters. Aquatic microbial
ecologists are only beginning to elucidate the
mechanisms of deactivation of viruses related
to microbial infections. Because little is known
about community dynamics of groundwater mi-
crobes, this is a potentially valuable and excit-
ing field for future study.

m in diameter, but larger and smaller ex-
amples exist and a modest variety of mor-
phologies occur (Fig. 8.3). The major groups
of bacteria, based on standard bacteriologi-
cal techniques, are presented in Table 8.2.
It is not known how many species of
bacteria exist, partially because of a funda-
mentally different species concept. Most ver-
tebrates and many of the plant species have
been described, but less than 1% of bacte-
rial species have been described (Young,
1997). Microbial diversity has received lim-
ited study because of difficulties associated
with identification in natural samples. Fur-
thermore, obtaining representative samples
in some habitats, such as groundwaters, is
difficult (Alfreider et al., 1997). The gut of
each invertebrate species could harbor sev-
eral unique microbial species, and each mil-
liliter of water or gram of sediment has
species that have never been cultured, so it
is possible that there are more species of Bac-
teria than any other type of organism.
Analysis of intensively studied hot spring
communities suggests that only a fraction of
the viable bacteria in any habitat can be cul-
tivated successfully with current techniques