Biology Reference
In-Depth Information
Bengtsson and Ovreas ( 2010 ) could show that Planctomycetes dominate in biofilms on
Laminaria hyperborea (up to 50% of all DAPI counts), and clone libraries generated
with a Planctomycete specific primer set revealed a high diversity of this phylum.
Thus, Planctomycetes might be underrepresented in clone libraries of microbial
communities of macroalgae studied so far. Whereas similar bacterial phyla are fre-
quently encountered (Table 10.1 ), algae specific populations, i.e., highly similar
(
97%) or identical in sequence could not be identified across all algal taxa examined
so far. Nevertheless, 16S rRNA gene sequences of
>
-proteobacterial
Rhodobacterales, Rhizobiales ( Mesorhizobium spp.), and Cyanobacterium spp. were
found as most frequent populations on red, brown, and green algal species (Barott et al.
2011 ; Burke et al. 2011b ; Lachnit et al. 2011 ;Meusnieretal. 2001 ; Tujula et al. 2010 )
(Table 10.1 ).
the
a
10.3 Host-Specific Microbial Communities on Macroalgae?
An important open question in alga-microbe interactions is whether these
associations are host-specific. A number of studies report that certain microbial
populations appear to be unique to the algal host but were absent in clone libraries
or DGGE patterns of the surrounding seawater (Bengtsson et al. 2010 ; Burke et al.
2011b ; Lachnit et al. 2011 ; Liu et al. 2011 ; Staufenberger et al. 2008 ), albeit some
overlap might exist at high taxonomic levels, i.e., phyla (Longford et al. 2007 ). The
surrounding seawater and sediment are likely sources of microbial recruitment for
algal surfaces. However, small microbial populations might be easily overlooked at
limited sample size possibly masking the presence of algal colonizers in seawater.
For example, a study on the kelp species Saccharina latissima (as Laminaria
saccharina ) involved 170 clones from the algal surface but only 31 clones from
seawater (Staufenberger et al. 2008 ); this is especially critical, as the seawater
microbial community was more diverse than that of the algal hosts according to
DGGE analysis. Nevertheless, the difference in composition between seawater and
algae suggests that algae provide at least a niche for a distinct microbiota. In fact,
different algal hosts from the same sampling site had highly dissimilar microbial
communities, suggesting that each algal host provides a unique niche for microbial
colonization (Barott et al. 2011 ; Lachnit et al. 2011 ).
A few studies report the existence of a “core” of specific microbial populations
on their host algae. For example, on the kelp species Laminaria hyperborea a
Planctomycete operational taxonomic unit (OTU) was commonly detected (78%
of all samples) over all seasons, albeit the OTU was defined relatively coarsely
(95% sequence identity; Bengtsson et al. 2010 ). Among the macroalgae from the
Baltic Sea, between 7 and 16% were identified as algal host-specific populations
(OTUs defined
99% sequence identity) across seasonal samples but still not all
OTUs were consistently present in summer and winter samples (Lachnit et al.
2011 ). The detection of a core microbial community is further complicated by
patterns of different microbial colonization along algal tissues, or might be subject
>
Search WWH ::




Custom Search