Marine Diatoms and Their Role in the Ecosystem

Diatoms are unicellular eukaryotic microalgae that play important ecological roles on a global scale. Diatoms are responsible for 20% of global carbon fixation and 40% of marine primary productivity. Thus they are major contributors to climate change processes, and form a substantial basis of the marine food web. At the cellular level, diatoms are characterized by having cell walls made of silica, and as the largest class of silicifying organisms on the planet, also are major contributors to biogeochemical processes. Diatoms are subject to varying environmental conditions from which they cannot readily escape, and so they must deal with environmental changes by altering cellular metabolism. Although measurement of environmental variables is relatively straightforward, the response of the organism is the critical determinant of the outcome of an environmental change. The organismal response comes from factors at the cellular level, hence monitoring changes in cellular processes is a potentially valuable approach to understanding how environmental factors drive ecological changes. The simplest way to evaluate changes in cellular processes is to monitor changes in gene expression – more specifically, changes in mRNA transcript levels. Our laboratory has focused on examining transcript changes in diatom transport protein genes in response to changes in environmental conditions, and determined that the responses can be complicated, and don’t strictly correlate with environmental changes. Two contributing factors to the lack of correlation are the interconnected nature of control mechanisms over different cellular processes, and the lack of correspondence between mRNA and protein levels resulting from translational regulation. There are several options to explore to improve the situation; 1) apply genome-wide surveys to attempt to identify genes that might serve as robust markers for environmental changes, 2) develop multi-gene evaluation approaches on model species with well established environmental responses, or 3) apply metagenomic approaches to environmental populations and determine whether correlation between expressed transcripts and environmental conditions occurs.