From the Field to the Lab: Community Analysis and Isolation of a Highly Branched Isoprenoid Producing Diatom, Nitzschia frustulum (Kütz.) Grunow (Bacillariophyta)

Abstract

Bacillariophyta (diatoms) are single-celled photosynthetic algae. Diatoms are found in most aquatic environments, and species occupy both benthic and planktonic areas. Some diatoms produce a molecule known as a highly branched isoprenoid (HBIs). HBIs are important molecules used in paleolimnology as a proxy for sea-ice reconstruction. In addition, there is evidence that HBIs can be used as a biofuel additive and have anti-cancer effects. It is not known what biological function and metabolic pathways diatoms use to produce HBIs. Through environmental and diatom community analysis, trends in species composition and environmental parameters can help us understand more about the production of HBIs. Growth analysis of isolated diatoms can further our understanding of the production of HBIs. In the present study, seven sites were selected for HBI and diatom community analysis. Common genera, including known HBI producers, match those in previous studies in other freshwater bodies of water. There are no clear trends between pH, temperature, and qualitative factors and the production of HBIs, indicating that other factors could contribute to this production, such as nutrient levels and the water conductivity. An HBI-producing diatom, Nitzschia frustulum, was isolated and used in growth analysis experiments. N. frustulum grows at an optimal pH of 7.5 to 8 at 25°C. HBIs were produced at a pH of 7 and at temperatures of 20°C and 25°C. C25 and C30 HBIs were found with varying amounts of unsaturation. The number of double bonds increased at a higher temperature. This study adds to the current understanding of the biological function of HBIs as potentially being involved in membrane fluidity.