Phylogeographic Analysis of Tick-borne Pathogen - Recent Advances and Issues in Environmental Science - page 87

The effect of MSP1a microsatellite size on gene expression was analyzed using the
sequence derived from Wetumka, Okeechobee, Idaho and HB-A8 A. marginale strains
(Table 6). The results showed that MSP1a expression was lower in the construct con-
taining the Idaho strain-derived MSP1a sequence with the lowest SD-ATG distance of
19 nucleotides, while differences were not observed between constructs containing the
MSP1a sequences from Wetumka, Okeechobee and HB-A8 A. marginale strains with
SD-ATG distances of 23 and 29 nucleotides (Table 6).

Table 6. Effect of microsatellite genotype on the expression of A. marginale MSP1a in E. coli.

A. marginale strain Normalized MSP I a mRNA levels

(arbitrary units)
ldaho,ID C 19 1.57 ± 0.29 (a)
Wetumka, OK G 23 2.31 ± 0.27 (b)
Okeechobee, FL G 23 2. 13 ± 0.0 (b)
HB-AS, China I 29 2.39 ± 0.19 (b)
MSP I a mRNA levels were analyzed by real-time RT-PCR in three independent clones for each of the MSP I a constructs
transformed in E coli JM I 09. MSP I a mRNA levels were normalized against E. coli dxs gene and plasmid DNA copy
number by msp I a PCR. Normalyzed MSPI a mRNA levels were represented in arbitrary units as average ± SD and
compared between different constructs using an ANOVA test (different letters denote signifi cant differences; P < 0.02).

Microsatellite
genotype

SD-ATG distance
(nucleotides)

DISCUSSION
Vector-borne pathogens have evolved molecular mechanisms of vector-pathogen
interactions that involve genetic traits of both the vector and the pathogen [5, 35].
For the tick-borne pathogen A. marginale , recent studies have characterized tick and
pathogen-derived genes that are involved in tick-pathogen interactions [2, 3, 6-9, 15].
Phylogenetic studies using tick and/or pathogen-derived genetic markers have contrib-
uted to our understanding of the evolution of A. marginale strains and tick-pathogen
relationships [5, 6, 20]. However, the impact of these studies has been limited by the
genetic diversity of genes involved in tick-pathogen interactions and thus are likely to
reflect pathogen evolution and tick-pathogen relationships [5].
In this study we took a different approach to characterize the evolution of A. marginale
strains. This is the fi rst study to use remotely sensed vegetation features as a surrogate
of an environmental envelope to which genetic variability and structure of a single
pathogen is associated. Biogeographic research seeks to identify the processes struc-
turing organism diversity at a variety of geographic and taxonomic scales [36]. Re-
mote sensing is being used increasingly as a tool to discover ecological traits through
defi nite signatures. NDVI is a measure of the vegetation stress, thus a time series of
NDVI values over a region refl ects the seasonal cycle of vegetation as a surrogate of
the seasonal variation in climate. NDVI and other climate features are commonly used
to detect ecologically suitable areas for some pathogens and their vectors [37-39]. For
example, Randolph and Rogers [40] indicated that climate has directed and constrained
the evolution of fl aviviruses of the TBE group. Six fl aviviruses (SSEV, WTBEV, Russian
TBEV, OHFV, and Kyasanur forest virus) fall within a distinct eco-climatic space
defi ned by factors derived from thermal and moisture conditions. Herein, we showed
that A. marginale MSP1a R1 repeats evolved under positive selection, were associated