Growth and biochemical responses of Skeletonema costatum to petroleum contamination

Clonal populations of the diatom Skeletonema costatum isolated from Lake Pontchartrain (Louisiana, USA) near the 2010 Deepwater Horizon oil release were exposed to uncontaminated f/2 medium or light slop oil emulsified (O-E; 25, 50, 75, 100 % of initial levels) in f/2 during short- (10 day) and long-term (21 day) incubations. During 10-day incubations, inhibition of logarithmic growth slopes occurred in the most severely contaminated populations (75, 100 % O-E f/2). Growth in oil-contaminated populations was reduced during 21-day incubations, and growth rates for all populations converged by ca. day 12. Additionally, total cell lipid contents for populations exposed to uncontaminated and contaminated media differed, and mean values for control populations were ca. 2-fold greater than populations maintained in 100 % O-E f/2 medium. Saturated and unsaturated cellular lipids in uncontaminated populations were greater than in petroleum-contaminated populations. Relative cellular fatty acids abundances and RuBisCO RNA transcript copy numbers, proxies for food storage and cellular stress, and mRNA transcript regulation influencing photosynthesis, respectively, were altered half-way through the long-term incubation; C16:0 and C16:1 fatty acids were greater and less, respectively, and RuBisCO transcript copy numbers were greater within severely contaminated populations (compared to uncontaminated populations). Yet, fatty acid abundances and RuBisCO copy numbers were equivalent among culture populations by the end of the incubation. Oil contaminants within the culture medium were measured; C6–C12 hydrocarbons and arsenic coincided with (initial) growth inhibition and (later) altered cell physiologies, respectively. Relationships among assessed parameters were deemed useful determinants for evaluating phytoplankton inhibition in response to petroleum contamination.