Abstract
BackgroundAmelioration of biofuel feedstock of microalgae using sustainable means through synthetic ecology is a promising strategy. The co-cultivation model (Tetraselmis striata and Pelagibaca bermudensis) was evaluated for the robust biofuel production under varying stressors as well as with the selected two-stage cultivation modes. In addition, the role of metabolic exudates including the quorum-sensing precursors was assessed.ResultsThe co-cultivation model innovated in this study supported the biomass production of T. striata in a saline/marine medium at a broad range of pH, salinity, and temperature/light conditions, as well as nutrient limitation with a growth promotion of 1.2–3.6-fold. Hence, this developed model could contribute to abiotic stress mitigation of T. striata. The quorum-sensing precursor dynamics of the growth promoting bacteria P. bermudensis exhibited unique pattern under varying stressors as revealed through targeted metabolomics (using liquid chromatography–mass spectrometry, LC–MS). P. bermudensis and its metabolic exudates mutually promoted the growth of T. striata, which elevated the lipid productivity. Interestingly, hydroxy alkyl quinolones independently showed growth inhibition of T. striata on elevated concentration. Among two-stage cultivation modes (low pH, elevated salinity, and nitrate limitation), specifically, nitrate limitation induced a 1.5 times higher lipid content (30–31%) than control in both axenic and co-cultivated conditions.ConclusionPelagibaca bermudensis is established as a potential growth promoting native phycospheric bacteria for robust biomass generation of T. striata in varying environment, and two-stage cultivation using nitrate limitation strategically maximized the biofuel precursors for both axenic and co-cultivation conditions (T and T-PB, respectively). Optimum metabolic exudate of P. bermudensis which act as a growth substrate to T. striata surpasses the antagonistic effect of excessive hydroxy alkyl quinolones [HHQ, 4-hydroxy-2-alkylquinolines and PQS (pseudomonas quorum signal), 2-heptyl-3-hydroxy-4(1H)-quinolone].
Highlights
Amelioration of biofuel feedstock of microalgae using sustainable means through synthetic ecology is a promising strategy
Effect of varying pH The total cell abundance of the microalgae under the T. striata and P. bermudensis (T-PB) condition with P. bermudensis and T conditions at different growth interval was the highest at pH 8.0 followed by pH 10.0, 6.0, and 4.0
This clearly indicates that the P. bermudensis provided a growth promoting environment for the T. striata under almost all the various pH conditions
Summary
Amelioration of biofuel feedstock of microalgae using sustainable means through synthetic ecology is a promising strategy. Most of the research in microalgal technologies has focused on elevation and amelioration of desired biological yields of the axenic or monoalgal strains without considering the potential of phycospheric bacteria [3, 4, 8, 9]. Limited research has been conducted on growth promoting sustainable cultivation techniques to ascertain the biomass productivity through biotic interactions despite the enormous potential of synthetic/natural co-cultivation. The metabolite and nutrients exuded by the phycospheric growth promoting bacteria could offer impressive biomass yields with suitable fatty acid properties to make biodiesel [10,11,12]. The mutualistic phycospheric bacteria can grow in similar physicochemical environments whenever co-cultivated, while it could not grow alone in the same media, and remarkable growth co-operation for the nutrients was shown which could reduce the cost of the cultivation [12]
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