The SAR11 clade and roseobacter clade are the two most abundant clades
in the marine environment, with almost 25% falling into the SAR11 clade and
slightly less falling into the roseobacter clade (Munn, 2012).With quantities
this high they must a large impact on their ecosystems, therefore research into
them is highly important.
Researchers can begin to understand the effect they have by
understanding the needs for these species to survive, in terms of nutrients,
temperature etc. Currently not much is known in this field currently. Giebel et
al (2010) investigated the context of environmental and biological properties of the North sea and compared them to the
abundance of roseobacter RCA and SAR11 linages. The properties they measured
included biogeochemical and microbial parameters: concentrations of chlorophyll a and
phaeopigments, suspended particulate matter, particulate
organic matter and particulate organic carbon. They also determined the rates of
bacterial production and
turnover rates of dissolved free amino acids.
Roseobacter clade affiliated
abundance was positively correlated with phaeopigments, chlorophyll a,
dissolved and particulate organic carbon, turnover rates of dissolved free
amino acids, temperature, and negatively correlated with salinity. The last
finding is interesting considering previous papers written: members of the Roseobacter clade do not occur in freshwater, demonstrating either a salt requirement
or tolerance (Buchan et al, 2005). This finding
seems to suggest
that high salt levels are actually detrimental to the bacteria.
This contradiction could
mean that Buchan et al’s theory is false, or it could demonstrate the
difficulty in describing such a large group. Buchan et al commented on the clade
in general, whereas Giebel et al investigated specifically the RCA linage. It
is possible that this linage has a lower optimum level of salt, and others have
a higher optimum.
Results
from this study were gained using a dilution method, which is more accurate
than culturing on agar plates (Munn, 2012). It consisted of diluting samples
followed by 109 days incubation at 15oC, before performing PCR. As this study
carried out experiments rather than just posing a theory, this is a more
reliable conclusion than Buchan et al stated.
The fact that Roseobacter clade is so large could mean that it is impossible to
describe the physiological properties of all species under this genus as the
same, therefore it is expected that research will provide varying results
depending on the specific species analysed. Although, a phylogenetic group
contains similar genetic information, and members of the same group should act
in a similar way. This highlights a problem with the classification system and
the difficulty in describing organisms.
Another interesting finding was that the SAR11 clade and the Roseobacter group seem to exhibit contrasting lifestyles. This has links to ecology in that it demonstrates how two organisms occupy completely different niches and still be extremely successful.
Future research should focus more a single or limited operational taxonomic units of the roseabacter clade in order to make clear comparisons and understand how variation occurs within the group. It is possible that members that have been described under this title should be reclassified.
Another interesting finding was that the SAR11 clade and the Roseobacter group seem to exhibit contrasting lifestyles. This has links to ecology in that it demonstrates how two organisms occupy completely different niches and still be extremely successful.
Future research should focus more a single or limited operational taxonomic units of the roseabacter clade in order to make clear comparisons and understand how variation occurs within the group. It is possible that members that have been described under this title should be reclassified.
Giebel HA, Kalhoefer
D, Lemke A, Thole S, Gahl-Janssen R, Simon M, Brinkhoff T (2010) Distribution of Roseobacter
RCA and SAR11 lineages in the North Sea and characteristics of an abundant RCA
isolate, ISME J 5: 8-19
Hi, this all sounds really interesting how completely different two clades of bacteria that are both present in the same conditions can be, but I'm a little confused about how the other papers come in to it - could you provide full references for the other papers that you have mentioned please? I was also wondering what the turnover rate of free amino acids shows us?
ReplyDeleteMegan –I think the main significance of this paper is that the Roseobacter clade seems more important than SAR11 in heterotrophic turnover in the North Sea, where there are pulses of higher nutrients. We know that this group is often closely associated with algal blooms as they decay. In the oligotrophic oceans, SAR11 seems more important, so it has a streamlined genome and it doesn’t respond to nutrient pulses. A key point of the paper was the elucidation the genome sequence of the cultured Roseobacter, which confirmed that it has much larger genome than SAR11, explaining its copiotrophic adaptability to nutrients.
ReplyDeleteHi Robyn, I referred to the last lecture by Collin and the paper by Buchan et al, which can be found here http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1265941
ReplyDeleteThe direct quote is: "With the exceptions of the described strains of the genus Ketogulonicigenium and several clones from a South African gold mine, the Roseobacter clade is exclusively marine or hypersaline, with characterized isolates demonstrating either a salt requirement or tolerance."
This is based on evidence from two papers that can be reached through hyperlinks embedded in the source linked above. I thought it was interesting how those papers seemed to support members of the Roseobacter clade living in high saline environment whereas the paper reviewed seemed to suggest higher salinity was not necessarily a positive factor. The fact that only a small minority can occur outside of marine environments suggests that salt is necessary, but this paper suggests that it is not a case of "the more, the better".
As for the meaning behind the turnover of free amino acids, the way I understand it is they are the amino acids in the environment that are available for use. As Collin said, this paper does have a large focus on the genome of the bacteria (which I did not mention previously as I felt there was too much detail to include when I was more interested in the aspects I mentioned in the initial post). Amino acids are used to produce DNA and RNA, and as members of the Roseobacter clade have a more complex genome they will have a larger turnover of amino acids than members of the SAR11 clade.
Hopefully this answers your question, feel free to say if you have any more questions or would like further explanation.
Collin - thank you, there was a lot of figures and tables and I must admit I got a bit lost amongst all the data!