The study conducted a microcosm experiment, in which the survival of the AltSIO strain was tested, using competition for nutrients and grazing pressure from protists as variables. Samples were collected in San Diego, California, from a range of depths between 0-100 m. The various treatments comprised of the seawater community, pure cultures of AltSIO and AltSIO with other bacterial cultures. Parameters such as cell counts, cell concentrations and concentration of DOC over 5 days (short-term) were measured to determine how microbial cell abundances and DOC changed over time.
The study found that AltSIO could potentially degrade as
much DOC as microbial assemblages with a high species diversity over the 5 days.
Over longer periods, however, overall microbial diversity was important for
degradation of recalcitrant DOM. The authors of the study suggested that this
was due to the various types of metabolism associated with high biodiversity
within the assemblages, enabling different bacteria to take advantage of the
DOM pool.
AltSIO is a large, fast-growing bacterium, making it able
to quickly respond to increases in substrate supply, reduced competition and
grazing pressure. AltSIO is able to effectively compete against smaller
bacteria for resources, regardless that smaller bacteria are theoretically
better able to acquire nutrients with an increased SA/V ratio. Being a large
bacterium, AltSIO is likely to be exposed to increased grazing pressure but variations
in the bacterivorous grazer populations do not explain the scenario entirely. Despite
this top-down control, this strain is able to persist and contribute a large
amount of carbon in the environment.
These properties that enable AltSIO to rapidly take
advantage of increased nutrient supply enhance its ability to degrade DOC
disproportionately, compared to the total bacterial biomass and abundance
within the ecosystem. Large bacteria may have a greater influence on DOM
recycling than previously thought and this asymmetry has important implications
for the fate of carbon, its role in the ecosystem and food webs.
This study alters our understanding of how bacterial
assemblage composition influences global carbon cycling and should be considered
when predicting the fate of carbon in the oceans. It would be interesting to
extend this idea to other coastal regions to determine if other dominant bacteria,
such as Pseudoalteromonas and Vibrio species, have this effect globally.
For those who wish to study this topic in more detail, the details of the
methods are in the supplementary information and I have included a link for
this with the link for the paper.Reference:
Pedler, B.E., Aluwihare, L.I., and Azam, F. (2014) Single bacterial strain capable of significant contribution to carbon cycling in the surface ocean, PNAS, 111, (20), 7202-7207.
Hi Anita,
ReplyDeleteFrom what I understood from the supplementary data although AltSIO consume a relatively large amount of carbon the ratio of carbon produced to carbon consumed is significantly less than that of the seawater community treatments (table S5). This could reduce the amount DOC recycled into the environment when AltSIO dominates.