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Co- culture systems are lately being explored as a potential replacement for monoculturing of various microorganisms in order to enhance the biomass yield, increase synthesis of described and yet unidentified bioactive compounds. Utilization of microalgae-bacteria co-cultivation has been well documented on wastewater treatment and downstream proccessing such as biomass harvesting. In contrast, very little data is known considering identification of novel metabolites produced only during co- cultivation. This area of research is of particular interest since most of these compounds have a great potential for medical and biotechnological application. Chlorella vulgaris is a model microalgae intensively investigated because of its ability to produce various bioactive compounds benefitial for human health. Streptomycetes are well known bacterial producers of antibiotics, anticancer and immunosupresssors. Abundantly present in soil, they are adapted to various ecological niches. Capacity to produce diverse metabolites is a result of their interaction with various organisms. Streptomyces rimosus G7 is specifically known for its ability of oxytetracycline production.In this study, S.rimosus and C.vulgaris consortium was cultivated in Triptic Soy Broth medium, under mixotrophic conditions. Reugular monitoring of growth curves served to detemine most relevant bioprocess parameters under which these organisms co-existed. Extracted biomass as well as metabolites excreted into the medium were invesitgated in order to determine the significant effects on their metabolomic flux. Determination of biomass composition of both microorganisms has been performed using Nile Red (NR) method with flourescence microscopy for lipid accumulation ; spectrophotometry for pigments and Lowry method for protein yield. Antimicrobial acitvity was tested using agar well diffusion method for detection of antibiotics.Co-culture systems resulted in increased yield of neutral lipids which identification and quantification of the fatty acids content was furtherly studied using gas chromatography (GC). Interestingly, antimicrobial acitvity of S. rimosus was tested using agar well diffusion method showing decreased antibiotic production in co- culture systems. Pigment content also decreased which can be linked to allelochemicals production, while protein composition remained the same.Optimization of bioprocess parameters of the co-culture system was successfully carried out in both Tryptic Soy Agar and Tryptic Soy Broth culture media. The total pigment content of chlorophyll a, b and pheophytin a, b was analysed regularly during co- cultivation. Moreover, the content of neutral lipids in the co- culture of C. vulgaris and S. rimosus (1:100 dilution) showed a significant increase in triolein production, which was 4, 353 mg/mL on the last day of cultivation. These results indicate the potential of co- culture systems for biodiesel production and still need to be confirmed by GC (gas chromatography). Interestingly, the antimicrobial activity assay showed that oxytetracycline was not produced in both C. vulgaris + S. rimosus 1:100 and 1:1000 dilution systems. This specific metabolic shift in co- culture systems will also be further validated by HPLC (high performance liquid chromatography). Metabolites synthesized and released in the culture medium, as well as those embedded in the biomass, will also be analysed by quadrupole time- of-flight (q-TOF) mass spectrometry to reveal the production of new compounds. |
