Bacterial presence within living
organisms has been investigated on a microbiological level and has been deemed
as a crucial component of a host’s health and success. The presence of varying
bacterial populations within coral is required to fulfil different symbiotic roles.
The bacterial community can be found within the tissue, mucus and skeleton of
coral, pointing towards the need for bacterial functions in different formats
within the organism’s structure. The fluctuation of bacterial populations,
occurring in conjunction with seasonal environmental changes, have previously
been investigated, however, no significant patterns have been identified.
Within the study by Li et al, 2014 the aspect of bacterial
community temporal fluctuations in the coral Porites lutea are addressed. Through sample gathering of P.lutea over a period of one year two
questions were addressed; whether bacterial communities changed in composition
in P.lutea with changes in season and
whether seasonal change in bacteria composition occurred within the three
compartments: tissue, skeleton and mucus. The samples of P.lutea were gathered at a depth of 3-5 metres, during February,
May, August and November of 2012, offering a balanced span of the seasons. At
the same time of coral sample collection samples of surrounding seawater were
also made for analysis of bacterial assemblage.
Identification of bacterial
assemblage was conducted through sequencing of the V1 and V2 regions of the 16s
rRNA gene. The highest count of bacterial species identified through sequencing
was found in the coral skeleton during February, with the lowest count being found
within the coral mucus during May. Through investigation of the coral structure
dominant species were found within certain temporal samples and diversity
varied throughout the seasons. The different niches provided by P.lutea also demonstrated variations,
with the bacterial assemblage of the mucus, skeleton and tissue showing greater
species diversity within the winter months compared to summer months. The dominant bacterial groups also varied when
examined at a lower taxonomic level, with similarities between each compartment
being calculated at just 24%-46%. In correlation with the coral 16s rRNA
sequencing results and using Shannon Weiner Index, the seawater diversity of
bacterial communities was highest during the month of February. However, in
contrast to the coral, surrounding seawater bacterial communities were
considerably stable throughout the different seasons, with Flavobacteria, Alphaproteobacteria
and Cyanobacteria being the dominant
classes.
These findings support the theory of P.lutea experiencing bacterial community
fluctuations due to seasonal environmental factors requiring different
symbiotic relationships. Further investigation of environmental parameters and
the corresponding response of bacterial community change were also
investigated. Two main factors which displayed a direct effect on bacterial
community assemblage were dissolved oxygen (DO) and rain fall. The change to an
increase of Bacilli during August corresponds with the increase of rainfall
within the summer months, and leads to the conclusion that the Bacilli could be
introduced to the coral through terrestrial fresh water runoff.
There were some seasonally and
compartmentally unrelated changes in bacterial community assemblage which were
observed during the study, these may point to numerous other influencing
factors upon the coral holobiont and its bacterial assemblage. The impact of
microbial communities from other surrounding organisms and seawater may
additionally affect the bacterial assemblage within the coral, along with
spatial differences on a longer term basis. Further study could be conducted
within these areas and possibly lead to a simplistic multidimensional model
being created, allowing an insight into the bacterial community assemblage of varying
coral holobiont communities which are yet to be investigated.
Li,
J., Chen, Q., Long, L., Dong, J., Yang, J. and Zhang, S. (2014) Bacterial
dynamics within the mucus, tissue and skeleton of the coral Porites lutea during different seasons. Scientific Reports. 4. 7320.
Hi Emma,
ReplyDeleteInteressting Post! I was wondering if the authors mentioned anything about the actual symbiosis, like the chemical processes, between these bacteria and the coral? Thinking back to Olavius algarvenis (the mouthless, gutless oligochaete worm), investigations into what all the different symbionts actually do, provided a lot of informations.
Hi Tabea,
ReplyDeleteThe nature of the relationship between the P.lutea and its associated bacterial communities are sparsley addressed within this study. Although, the possibility of the bacteria Prosthecochloris
and Clostridium (existing in the coral tissue) being present in a nitrogen fixing relationship with the coral is hypothesised. The study ststes these two bacteria are possible nitrogen fixers and references the paper Chen, J. S., Toth, J. & Kasap, M. Nitrogen-fixation genes and nitrogenase activity in Clostridium acetobutylicum and Clostridium beijerinckii. J. Ind. Microbiol. Biotechnol. 27, 281–286 (2001). The spring collection of mucus bacteria community posses a high abundance of vibrio, they are viewed as possible healthy community structures, though there is little evidence produced within this paper to support this. I hope this answers your question. It would be interesting to see if there are any further papers on the bacterial community relationship with the coral P.lutea, I must admit host/symbiont relationships seem to have a lot to teach us, I hope to see more posts on these relationships.