Biology Reference
In-Depth Information
LL
for 25 days
Initial
composition
LD 12: 12 h
for 30 days
WT (25 h)
CLAb
CLAc
WT (25 h)
Rescue (25 h)
WT (25 h)
Figure 7:
Competition between rhythmic and arrhythmic strains of cyanobacteria
.
Mutant strains with arrhythmic (CLAc),
or dampened (CLAb) bioluminescence rhythm, as well as the rescued strains were competed against wild type strain
under periodic and constant environments (LD cycles and LL, respectively). Rhythmic strains out competed the wild type
strain under LD cycles, but the arrhythmic strains out competed rhythmic strains under LL. Middle panels represent initial
composition of the competing strains. Values in the parenthesis indicate the free-running period of the cyanobacterial strains.
(Figure modifi ed after Woelfl e
et al.
, 2004). With kind permission of V. K. Sharma, Chronobiology Laboratory, Evolutionary
and Organismal Biology Unit, Jawaharlal Nehru Centre for Advanced Scientifi c Research, Jakkur, PO Box 6436, Bangalore
560 064, Karnataka, India [Paranjpe, D. A. and Sharma, V. K. (2005)
J
Circadian Rhythms
3:
7 doi:10.1186/1740-3391-3-7].
only
kaiBC
sequences are present in this organism and KaiC exists in a hyperphosphorylated state.
It is suggested that this evolutionary reduction in the clock components would suffi ce the timing
mechanism in view of the stable environment in which the organism grows (Axmann
et al
., 2009).
The genome streamlining of
P
.
marinus
PCC 9511 resulted in loss of robustness of the circadian
clock. Holtzendorff
et al
. (2008) demonstrated that though there is a diurnal variation in the mRNA
levels of
kaiBC
operon and certain other selected genes such as
psbA
expression rhythms, under LL
condition the robustness of the rhythm is lost. Though
kaiBC
gene sequences are present and the
essential properties of KaiC are well conserved in
Legionella pneumophila
, an opportunistic human
pathogen, their functional organization is yet to be uncovered (Lozza-Correa
et al
., 2010).
The structure and molecular phylogeny of
sasA
genes in cyanobacteria revealed that
sasA
occurred in a single copy. Two Clades, Clade A and Clade B have been recognized. Clade A has
been shown to be associated with species possessing all the three
kai
genes while Clade B was
