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350 IJSR - INTERNATIONAL JOURNAL OF SCIENTIFIC RESEARCH
Volume : 2 | Issue : 9 | September 2013 • ISSN No 2277 - 8179 Research Paper
Microbiology
Dharmesh Harwani
Department of Microbiology, Maharaja Ganga Singh University, NH-15, Bikaner
334001, INDIA
ABSTRACT
in vitro. These microscopic cells are considered to be dead and therefore would never grow posed the anomaly without classifying
them. In fact, many of these cells were shown to be metabolically active, even though they were not able to grow on laboratory media.
The Great Plate Count Anomaly and the
Unculturable Bacteria
KEYWORDS : Anomaly, Plate count,
Unculturable bacteria
THE GREAT PLATE COUNT ANOMALY
The great plate count anomaly is the observation that most of
the microbes seen in the microscope cannot currently be grown
under laboratory conditions, some may actually be nonviable,
others are viable but nonculturable (VBNC). The term “the great
plate count anomaly” was coined by Staley and Konopka (1985)
to describe the difference between the numbers of cells from
natural environments that form viable colonies on agar me-
dium and the numbers obtained by microscopy (Fig. 1). There
are several explanations for this great plate count anomaly. For
example, species that would otherwise be “culturable” may fail
to grow because their growth state in nature, such as dormancy,
prevents adjustment to conditions found in laboratory where
nutrient rich media are used for the plate counts (Deming &
Baross, 2000). If an organism has a low prevalence or is par-
ticularly slow growing it is highly likely that it may have been
over looked in the laboratory cultural analyses. Many geneti-
cally distinct phenotypes are phenotypically indistinguishable
for example some bacteria are resistant to culture on conven-
tional media, certain bacteria have fastidious growth require-
pH conditions, incubation temperatures or levels of oxygen in
the atmosphere (Kopke et al. 2005).
Figure 1. The Great Plate Count Anomaly
Many microorganisms are oligotrophic in nature and require
fastidious conditions for successful culture. Further there may
be competition for nutrients among mixtures of organisms cul-
tured together. Growth may also be inhibited by bacteriocins
released from other bacteria in a mixed culture or by antibacte-
rial substances present within the medium (Tamaki et al. 2005).
each other on a surface. This includes quorum sensing mecha-
nism that is involved in the regulation of the bacterial commu-
nity structure; properties and survival (De Kievit et al. 2001).
Signaling molecules present only within the natural habitat are
thought to be essential for the growth of many bacteria. In the
Discrete B acterial
Colonies
Dilution Plating
Environmental Sample
Microscopy
~99% bacteria
Un-culturable
Nutrient A gar Plate
Only ~ 1% Bacteria
Culturable
-
an unfamiliar environment devoid of essential factors (Nichols
et al. 2008). Many of microbial strains that are common in na-
ture can only be cultured by specialized techniques (Baxter &
Sieburth 1984, Boogerd et al. 1989, DeBruyn et al. 1990, Koops
& Moller 1992, Ferris et al. 1996, Nold et al. 1996, Partensky et
al. 1996, Schut et al. 1997, Button et al. 1998, Vancanneyt et al.
2001, Wirsen et al. 2002).
THE EVIDENCE FOR THE UNCULTURED
BACTERIA
The evidence for the presence of uncultured bacteria that can-
not be grown in the laboratory came from molecular data. The
ability to obtain DNA sequence information from an environ-
mental sample (regardless of their viability in laboratory con-
such as 16S rRNA gene sequences (Amann et al. 1995). Such
sequence information uncovered a hidden treasure of bacterial
diversity that had never been acknowledged by routine culti-
vation. Woese described 11 bacterial phyla in 1987 which has
been grown now to at least 85 divisions, majority of which have
no cultured representatives (Woese 1987, Rappe & Giovannoni
2003, Keller & Zengler 2004, Achtman & Wagner 2008). The
rapid appearance of members of the uncultured phyla indicates
their presence in an environment. For example the TM7 phylum
has been detected frequently in many different environments. A
discovered in peat bogs (Rheims et al. 1996) and it has been
reported to be present in a diverse ecological conditions which
include soil, water, waste treatment sludge, marine sponges and
the human micro-biome (Hugenholtz et al. 2001, Hardoim et al.
2009, Bik et al. 2010, Dinis et al. 2011).
CATEGORIES OF THE UNCULTURABLE
BACTERIA
-
sitic bacteria. These bacteria expand under the host provided
Prochloron
didemni, Cristispira, Holospora, Caedibacter, Lyticum, Blattabac-
terium and rickettsiae. In the second category, viable but non
culturable organisms have been included. Though these organ-
isms are viable in natural conditions but fail to undergo cell
division on routinely used growth media. Cells of many native
marine bacteria have been tested by a number of methods to
address particularly these issues which have been observed to
(Colwell et al. 1985).
CONCLUSION AND FUTURE
PERSPECTIVE
Microbial diversity analysis of unculturable bacteria has re-
vealed previously uncharacterized members in bacterial do-
mains. These novel unculturable bacteria represent an un-
explored and unexploited vast gene pool. Genomic library
construction of unculturable members of various bacterial
-
ery. Availability of community genome sequences will help in
IJSR - INTERNATIONAL JOURNAL OF SCIENTIFIC RESEARCH 351
Volume : 2 | Issue : 9 | September 2013 • ISSN No 2277 - 8179
Research Paper
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In addition to that an
access to the neglected bacteria that reside on us may provide
new avenues to improve overall health through an enhanced
understanding of the yet unknown functionalities. Although ad-
vances in recent research have shown that members of bacterial
groups that were previously considered to be unculturable can
now be cultured, a major part of the existing bacterial diversity
still remains cryptic due to their culture recalcitrance.