Biofilms Under the Influence of Acid and Ice

Chair: Sean Connell

Shane M Powell (1)*, Laurence J Clarke (2,3), Bruce E Deagle (2,3), Jonathan S Stark (2)

1 School of Land and Food, University of Tasmania, Hobart, Tasmania, 7005, Australia
2 Australian Antarctic Division, Kingston, Tasmania, 7050, Australia
3 Antarctic Climate & Ecosystems Cooperative Research Centre, University of Tasmania, Hobart, Tasmania, 7001, Australia

Background
Biofilms are complex communities existing in a matrix of extracellular polymeric substances. Biofilms are initially constructed by bacteria but mature biofilms contain a range of organisms interacting with each other and their environment. Hence they provide an ideal model community on which to study the effect of environmental changes.

Methods
In the 2014-2015 Antarctic summer, a free ocean carbon enrichment experiment (antFOCE) was carried out in the nearshore environment at Australia’s Casey station for approximately 8 weeks. There were three treatments: two acidified chambers (at 0.4 pH below ambient); two control chambers (ambient pH); and two open plots (no chamber). In this experiment glass slides were used as a substrate for the growth of biofilms in all treatments, which were sampled at two times, 4 weeks (January) and 8 weeks (February). DNA was extracted from the biofilms and high throughput amplicon sequencing was used to examine the composition of bacterial, archeal and eukaryotic communities.

Findings
Complex and dynamic communities were observed in the nearby environment and within the chambers. The communities were influenced by the time of sampling (January or February) and by whether they were collected from within the chamber or the external open environment. At some of the time points, clear differences were observed between the communities in the control and acidified chambers. The bacterial communities were typical marine communities dominated by the Gammaproteobacteria, Alphaproteobacteria and Flavobacteriia. Half the eukaryote taxa that were more abundant in the acidified treatment compared to the control were identified as Bacillariophyta, whereas Dinophyceae and Cercozoans tended to be less abundant on slides from the acidified chambers.

Conclusions
Although we observed a distinct ‘chamber effect’, differences in the communities between the acidified and control chambers suggest Antarctic biofilm colonisation dynamics may be altered in a high CO2 world.