Does substrate type effect bacterial community composition of biofilms from the Great Barrier Reef?

Many factors influence the formation and composition of biofilms such as nutrient availability, water depth, salinity and temperature. Because biofilms respond rapidly to changes in these environmental parameters they have been used as bioindicators of water quality. Other studies have previously investigated these parameters but have neglected to look at the effect of growth substrate on community composition. Two studies which have looked at this effect have been limited to only artificial substrates. This means that it is difficult to know whether the biofilm communities growing on these artificial substrates have similar community composition to those that grow in natural situations. A factor which is important in many fields of research for example when using biofilms as bioindicators. The study by Witt et al. (2011) therefore aimed to investigate the effect of different settlement substrates (natural and artificial) on biofilm communities in situ therefore providing a better rationale for future bioindicator studies of water quality in this type of ecosystem.

Four different substrates (glass slides, ceramic tiles, reef skeletons and reef sediments) were deployed in situ for 48 days at two locations in the Whitsunday Island Group (Central GBR) in summer and winter. Bacterial community composition was studied using PCR amplification of 16S rRNA genes and Terminal restriction fragment length polymorphism analysis (T-RFLP) which is a molecular method used to gain a fingerprint of an unknown microbial community.

The authors found that biofilm communities were similar on all settlement substrates and Principal Component Analysis (PCA) showed that bacterial communities were largely overlapping for all substrate types. Glass slides and coral skeletons were shown to be most similar. The inshore location which is heavily influenced by water quality changes through the season showed significant differences between reef sediments and other substrate types. This substrate also showed the most variability in bacterial community composition. The authors suggest that this may be due to the fact that the reef sediments have low reproducibility. Relatively variable bacterial communities were also found on ceramic tiles. Taking these factors into consideration the authors state that glass slides enable the formation of biofilms closest to that on natural substrates (coral skeleton and reef sediment).

This study provides evidence that glass slides are the best substrate type to use as a comparison to natural substrates and therefore provide a basis for further work looking using biofilms as a bioindicator for water quality. Further work looking at seasonal changes bacterial community structure in varying water quality.

Witt V., Wild C., Uthicke S. (2011) Effect of substrate type on bacterial community composition in biofilms from the Great Barrier Reef. FEMS Microbiology Letters 323: 188-195.