MICROALGAE INCLUSION AFFECTS BACTERIAL COMMUNITY COMPOSITION IN RECIRCULATING AQUACULTURE SYSTEM

Norulhuda Mohamed Ramli *, C. Giatsis, F.M. Yusoff, J.A.J Verreth and M.C.J Verdegem
 
Wageningen University and Research
Current address;
Department of Biological and Agricultural Engineering
Faculty of Engineering, Universiti Putra Malaysia
43400 Serdang, Selangor, Malaysia
norul49huda@gmail.com
 

Literatures provide untested observations that fish in the green water are more vital, robust and less sensitive to diseases than those reared in algae-free systems. We hypothesized that the underlying mechanism could be related to the vitality of the microbiota in the system.

In this study, the inclusion effect of microalgae on bacteria community in recirculating aquaculture system (RAS) was investigated. The RAS with microalgae (RAS+A) used in this study included a fish tank (65 L), a sedimentation tank (42 L), a moving bed reactor (nitrification tank) (14 L), two units of microalgae tank (14 L each) and a sump (112 L). RAS without microalgae (RAS-A) had the same set up as RAS+A, except that the tank for microalgae was filled with water and contained no microalgae. To determine the water bacterial composition, water samples from the fish, nitrification and microalgae tanks were collected at the start of the experiment (d0) and on the final day of the experiment (d28). Bacteria community in the system was analysed using denaturing gradient gel electrophoresis DGGE (for day 0 and 28) and 16S metagenomic analysis using Illumina MiSeq technique (Illumina Inc, San Diago, USA) (for day 28).

PERMANOVA test using Bray-Curtis resemblance matrix from DGGE data showed a significant difference of bacterial community between treatments  (RAS+A and RAS-A). 16 S metagenomic analysis revealed 5561 operational taxonomic units (OTU) at a similarity threshold of 97% which were grouped into the bacteria domains. No difference of bacterial community composition based on 16 S metagenomic was found between RAS+A and RAS-A (Pseudo-F = 3.9; P-value = 0.056; Unique permutations = 60). Nonetheless, similarity percentage analysis (SIMPER) showed that algal-associated bacteria were more abundant in the RAS+A than in the RAS-A.

This finding suggested that microalgae inclusion could influence bacterial community in the RAS. In the future, the role of microalgae to steer bacterial community to the desired composition should be explored.