Identification and characterization of microorganisms potentially beneficial for intensive cultivation of Penaeus vannamei under biofloc conditions: Highlighting Exiguobacterium acetylicum

The aim of this work was to isolate, identify and characterize microorganisms present in intensive nursery of Penaeus vannamei during the spontaneous generation of the biofloc and to verify among the isolates, beneficial strains for the intensive cultivation of shrimp under biofloc conditions. 91 strains were isolated and identified by molecular taxonomy. Then, the strains were analysed for the presence of the aiiA gene responsible for the inherited transmission for the production of lactonase. Only Exiguobacterium acetylicum presented the expressed aiiA gene. E. acetylicum was tested for its proteolytic, amylolytic and lipolytic inhibition activity. Inhibition capacity against pathogenic bacteria was 1.47 mm, 2.0 mm and 1.5 mm halo for Vibrio alginolyticus V. harveyi and V. parahaemolyticus, respectively. The mass production process of the E. acetylicum inoculum was standardized at a concentration of 1.58 x 107 CFU/ml and was applied in two treatments with three replicates each. One group received a weekly application of the inoculum while another group received a biweekly application. A control group received no application of the inoculum. Then, the effect of enriching the intensive culture medium for P. vannamei with E. acetylicum under biofloc conditions was evaluated. At the end of the 21-day trial, the survival and average productivity were statistically higher in the groups that received the application of the bacterial inoculum. The data suggest that the presence of E. acetylicum bacteria in the growth phase of P. vannamei significantly increased survival (90.9 ± 6.0%) and productivity (1.42 ± 0.16 kg/m3).