Media optimization and lipid formation of two native diatoms for cultivation in the Southwest Texas desert

Abstract

Two native diatom isolates belonging to the genus Nitzschia, TAMU-LBK-020 and TAMU-LBK-023, were grown in a chamber simulating summer temperatures and light:dark cycle in the southwest Texas (USA) desert. Different concentrations of macronutrients (Si, N, and P) were tested to identify conditions conducive to growth. Growth rates of the fastest growing treatments exceeded 0.6 doublings per day, with DW and AFDW exceeding 1.0 and 0.8 g L−1, respectively. Treatments with positive growth were continued to a lipid formation step by omission of Si from the medium in this phase, with lipid accumulation monitored daily by Nile red fluorescence. Peak oil was observed at approximately day 3 for TAMU-LBK-020 and day 5 for TAMU-LBK-023. The highest oil concentrations observed were 17.5 ± 7.3 % of AFDW in TAMU-LBK-020 and 28.5 ± 5.6 % of AFDW in TAMU-LBK-023 at low N concentrations, but the low N also resulted in growth of 0.2 to 0.5 doublings per day. We propose a biphasic growth strategy, initially under a high macronutrient concentration to promote cell growth and division followed by starving for Si and N to achieve maximal lipid production. However, we anticipate that it will be necessary to determine optimal nutrient concentrations empirically for each species and strain. These results demonstrate that diatoms used for biofuels can achieve fast growth rates and high oil production, and also that native strains, when properly cultured, can be highly suitable for biofuel production, even in harsh climates such as the desert Southwest U.S.