Co-culturing bacteria and microalgae in organic carbon containing medium.
BACKGROUND
Microalgae frequently grow in natural environment and long-term laboratory cultures in association with bacteria. Bacteria benefit the oxygen and extracellular substances generated by microalgae, and reimburse microalgae with carbon dioxide, vitamins and so on. Such synergistic relationship has aided in establishing an efficient microalga-bacterium co-culturing mode. Obviously, the mutually beneficial relationship can be strengthened with the increase of the densities of microalgae and bacteria. However, nearly all of the early co-cultures were performed under photoautotrophic conditions, thus both microalgae and bacteria were at relatively low densities. In this study, the feasibility of bacteria-microalgae co-cultured under mixotrophic conditions was studied.


RESULTS
Firstly, bacteria mingled with xenic microalgae were isolated and identified based on their 16S rRNA gene sequence (16S rDNA hereafter). Then, the two most frequently found strains of Muricauda sp. were co-cultured with axenic microalga (Tetraselmis chuii, Cylindrotheca fusiformis and Nannochloropsis gaditana) in extra organic carbon containing medium. At the end of a co-culture period of 33 days, we found that the final cell density of T. chuii and C. fusiformis of various treatments was remarkably higher than that of controls (21.37-31.18 and 65.42-83.47 %, respectively); on the contrary, the growth of N. gaditana was markedly inhibited. During the co-culture of bacteria with C. fusiformis, the cell density of two strains of bacteria firstly decreased, then increased and maintained at a relatively steady level. However, the cell density of bacteria performed a sustaining downward trend when they were co-cultured with T. chuii and N. gaditana.


CONCLUSIONS
Our findings proved that microalgae-bacteria co-cultures under mixotrophic conditions are quite effective strategy for microalgal cultivation.
Laboratory of Applied Microalgae Biology, Ocean University of China, Qingdao, 266003 China.
Jichang
J
Han
Laboratory of Applied Microalgae Biology, Ocean University of China, Qingdao, 266003 China ; Key Laboratory of Marine Biotechnology, Ningbo University, Ningbo, 315211 China.
Lin
L
Zhang
Laboratory of Applied Microalgae Biology, Ocean University of China, Qingdao, 266003 China.
Song
S
Wang
College of Marine Life Sciences, Ocean University of China, Qingdao, 266003 China.
Guanpin
G
Yang
Laboratory of Applied Microalgae Biology, Ocean University of China, Qingdao, 266003 China.
Lu
L
Zhao
Laboratory of Applied Microalgae Biology, Ocean University of China, Qingdao, 266003 China ; Function Laboratory for Marin Fisheries Science and Food Production Processes, Qingdao National Laboratory for Marine Science and Technology, Qingdao, 266237 China.
Kehou
K
Pan
Bacteria; Microalgae; Microalgae-bacteria co-culture; Mixotrophy