Biofilms - Saviours of the Intertidal Zone

Microbial biofilms found in intertidal zones are vital in conserving energy and materials, and maintaining this environment. Biofilms (composed of diatoms, protozoa, fungi, bacteria and archaea), are essential for supplying grazers and their predators with energy. They secrete extracellular polymeric substances (EPS), produced by photosynthesis and composed mainly of glucose. This is then passed on to the heterotrophic organisms, and acts as a stabiliser of the environment.

This regulation of energy transfer and recycling of material make biofilms extremely dynamic. Biofilms in the intertidal zone are also impacted by the stressors in this environment, such as light stress, desiccation, and extreme changes in temperature, salinity and pH. These factors have a major impact on the properties of the biofilms.

A review conducted by Van Colen et al. (2014) looks into the current knowledge on the ecological processes within biofilms, in particular looking at the production of EPS, photophysiological stress responses and the role of grazer interactions.

EPS is an integral part of the benthic microbial food web, and is a major carbon source. The carbon contained within this molecule can be traced into the phospholipid fatty acids and RNA of many bacterial groups within the biofilm. The activity of the bacteria using EPS may positively impact other microbial groups; however this is not fully understood. Past work has focused on EPS use in aerobic conditions. For more insight into microbial interactions, this paper stresses the necessity to understand the anaerobic pathways utilised by biofilms as well.

Light stress can affect biofilm primary productivity by increasing the amount of reactive oxygen species (ROS). This decreases primary productivity, and affects EPS production. Photoinhibition then occurs in two methods of photoprotection: an effective xanthophyll cycle and vertical migration. It is proposed that these methods allow the biofilms to successfully regulate their light exposure. While work has been completed using chlorophyll fluorescence imaging and inhibitors of the processes, the results have provided indirect evidence of the biogeochemical processes occurring within the biofilm. It is suggested that studies should focus on the specific photoprotection processes in order to understand how the biofilms avoid light stress, as well as further photoinhibition.

Recent studies have shown that the biofilms are able to stabilise their environment due to the production of EPS, which binds particles together. The biofilm biomass has been shown to have an effect on erosion thresholds, and so little/no biofilm equals increased erosion. The activities of grazers and predators can also disrupt biofilms, and so the environment is more susceptible to erosion. The macrobenthos population dynamics are very tightly linked to spatio-temporal dynamics of the biofilms, which means that biofilms are shown to play a massive role in understanding the bio-physical interactions that occur within the intertidal environment. This has revealed a much more complex and ever changing ecological system.

Recent findings will often make the marine microbial picture more complicated, and show how much more is left to determine. However, it is also important to note that new technologies allow for more microbial discoveries to be made than ever before. This paper is useful in reviewing our total biofilm knowledge, and shows how this field of microbial study can be moved forward during these environmentally uncertain times. What would be interesting to see in the future is how the ongoing anthropogenic activities impact biofilm processes, and if the environment is adapting to these introduced stressors.

Van Colen, C., Underwood, G., Serôdio, J., Paterson, D. M., (2014) 'Ecology Of Intertidal Microbial Biofilms: Mechanisms, Patterns And Future Research Needs'. Journal of Sea Research 92 : 2-5. Web.

http://www.sciencedirect.com/science/article/pii/S1385110114001166