Co-culturing of Chlorella vulgaris and bacteria at laboratorial scale

Abstract

The industrial production of axenic Chlorella vulgaris is very challenging as bacterial contaminations are common both in open and closed cultivation systems. Some microalgae and bacteria can establish symbiotic relationships in which both microorganisms benefit from one another, that can result in improved growth and culture robustness. This strategy would be advantageous to co-cultivate C. vulgaris with a well-known starter culture of bacteria that is able to promote the microalga’s growth. The benefits would be: the establishment of a symbiotic relationship that could improve the growth rates of C. vulgaris and the presence of a beneficial bacteria consortium that would prevent the occupation of those niches by unknown and detrimental bacterial contaminants.The aim of the present work was to find bacterial species that could establish a symbiotic relationship with Chlorella vulgaris strain, in co-culture, to improve the latter’s growth and culture robustness. Thereby, bacterial strains that had previously been isolated from pilot scale cultures of C. vulgaris in mixotrophic conditions were co-cultivated with this microalga. Also, a commercially available culture of Lactic Acid Bacteria was tested in co-culture with C. vulgaris. The growth of these microorganisms and the constitution of the ecosystems was evaluated throughout time.Results from this study suggested that two bacteria (LL_Bc07 and LL_Bc11) may have a positive impact on C. vulgaris in batch mode while one bacterial isolate (LL_Bc02) may have a negative impact, under the same conditions. On the contrary, in semi-continuous regime, bacterial consortia did not affect the growth of the microalga. It was clear that LAB did not grow well in the mixotrophic medium used, as they are fastidious bacteria. Therefore, the microalga’s growth was not affected by the presence of LAB. Regarding community stability, co-cultures containing two of the bacterial isolates LL_Bc02, LL_Bc07 and LL_Bc11, kept their composition stable from the beginning to the end of the test. On the contrary the monoalgal control and the mixed culture containing C. vulgaris and LAB suffered contaminations from one or more of the bacterial isolates.

Date of Award	6 Feb 2018
Original language	English
Awarding Institution	Universidade Católica Portuguesa
Supervisor	Luís Tiago Marques Guerra (Supervisor) & Joana Gabriela Laranjeira da Silva (Co-Supervisor)