Erythromycin-mediated complete co-flocculation between cyanobacterium and Penicillium: the easy-to-harvest co-cultivation without organic compound that increased CO2 fixation and biomass production.
Photoautotrophic cyanobacteria convert CO2 and produce various bioproducts. However, effective cell harvesting from liquid cultivation is a main obstacle. Automatic bio-flocculation provides a potential solution. In a Synechocystis sp. PCC 6803 (Syn) culture, we found that Syn co-flocculated with the natural contaminated fungi (identified as Penicillium sp.) as sphere biomass cluster with space inside, under the treatment of antibiotic erythromycin, but not without erythromycin. The optimized co-cultivation for five days using the initial Syn density of 0.4 OD730, 5 mg/100 ml fresh weight of Penicillium inoculum, and 5 µM EM in the BG11 medium with no organic compounds produced a complete biomass co-flocculation up to 2.0 g/L, equivalent to the atmospheric CO2 capture of 0.6 g/L/d: the 7.9-times biomass level and 7.2-times CO2 capture amount performed by the axenic Syn culture. A major constituent in Syn-Penicillium flocculated biomass is protein contents ranging from 39-61% of dry weight. In addition, increasing EM concentrations (from 0.3 to 10 µM) enlarged the co-flocculate diameter from x to Y and increasing the culture volumes (from 100 to 200-400 mL) altered co-flocculate surface texture from relatively smooth to rough with thorns. This co-flocculation may be further developed for CO2 capture and biomass utilization as amimal feed with a high protein contents. Syn with Penicillium_1; Synechocystis with Penicillium replicate 1 Syn with Penicillium_2; Synechocystis with Penicillium replicate 2 Syn with Penicillium_3; Synechocystis with Penicillium replicate 3 Syn without EM_1; Synechocystis without Erytromycin treatment replicate 1 Syn without EM_2; Synechocystis without Erytromycin treatment replicate 1 Syn without EM_3; Synechocystis without Erytromycin treatment replicate 1 Syn with EM_1; Synechocystis with Erytromycin treatment replicate 1 Syn with EM_2; Synechocystis with Erytromycin treatment replicate 1 Syn with EM_3; Synechocystis with Erytromycin treatment replicate 1 LR_Syn with Penicillium with EM_1; Large star structure of Synechocystis with Penicillium under EM treatment replicate 1 LR_Syn with Penicillium with EM_2; Large star structure of Synechocystis with Penicillium under EM treatment replicate 2 LR_Syn with Penicillium with EM_3; Large star structure of Synechocystis with Penicillium under EM treatment replicate 3 SS_Syn with Penicillium with EM_1; Small smooth structure of Synechocystis with Penicillium under EM treatment replicate 1 SS_Syn with Penicillium with EM_2; Small smooth structure of Synechocystis with Penicillium under EM treatment replicate 2 SS_Syn with Penicillium with EM_3; Small smooth structure of Synechocystis with Penicillium under EM treatment replicate 3 Overall design: Transcriptomic analysis was performed between the Synechocystis in the suspended Synechocystis cells with EM and the Synechocystis cells in the flocculated (with the Penicillium) Synechocystis-Penicillium flocculated biomass.  The results suggested that the presence of Penicillium did not significantly altered the expression levels of pillin genes. Thus the altered gene expression levels of pillin genes were results from the EM treatment. Samples include,Syn with Penicillium_1;