EFFECTS OF ASSOCIATED BACTERIA ON Phaeodactylum tricornutum BIOMASS AND GROWTH RATE

Bacteria are known to have beneficial (e.g., production of signaling/inducer molecules, nutrient release) and adverse (e.g., competition and pathogenic interactions) effects on algal growth rates and metabolite production. The potential for enhancing biofuel production using bacteria prompted this assessment of the impact bacterial-algal associations on algal biomass production.

An axenic strain of P. tricornutum and and the same algal strain co-incubated with bacterial isolates were grown in 1L flasks in triplicate and sampled for 20 days. Growth rates of the different co-cultures of P. tricornutum/bacteria and the axenic samples were measured using OD, HPLC pigment analysis, and cell counts. Correlations were made between all of the proxy measurement and cell counts. Bacterial identification was accomplished by 16S rRNA gene sequencing. HPLC-TOF was used to identify compounds associated with axenic and mixed cultures.

Growth rates were calculated from cell counts (Figure 1). Enhanced growth occurred in some bacterial-algal cultures relative to axenic cultures in both exponential and linear phases (p. < 0.05). Correlations of proxy and direct cell counts indicated strong linearity for optical density at both 655nm and 750nm (Table 1).  Two different species of bacteria were identified through bacterial 16S sequencing; the most common was Oceanicaulis alexandrii.  O. alexandrii has previously been isolated from dinoflagellate and coral cultures. Eicosapentaenoic acid (EPA) was found in higher quantities in bacterial:P. tricornutum isolates than in axenic isolates. Ongoing work will use HPLC-TOF to identify regulated bioactive metabolites in bacterial-algal cultures.

Supported by: Part of this work performed under the auspices of the U.S. Department of Energy at Lawrence Livermore National Laboratory under Contract DE-AC52- 07NA27344 and the TAMUCC Center for Coastal Studies by DOE-BER's Genomic Sciences Program under the LLNL Biofuels SFA FWP SCW1039-02.