Simultaneous Growth of <i>Chaetoceros muelleri</i> and Bacteria in Batch Cultures

Abstract

The relationship between bacterial load and the microalga Chaetoceros muelleri was analyzed in a scale-up experiment. The microalga was grown during five days in a 0.4-L Erlenmeyer flask, 2-L Fernbach flask, 18-L Carboy and 400-L column, during which the cell density of C. muelleri, the abundance of heterotrophic bacteria, Vibrio spp., and total bacteria were determined. The h ighest specific growth rates (μ) of C. muelleri occurred during the first day of culture (0.88 to 2.29 d -1 ). Highest cell density was recorded on the fifth day at the 2-L (7.62 × 10 6 cells·mL -1 ) and 18-L (6.32 × 10 6 cells·mL -1 ), coinciding with the maximum counts of heterotrophic bacteria (16.55 × 10 5 and >30 × 10 5 CFU·mL -1 , respectively). There was a high correlation (0.80, 0.75, 0.85; p <0.05) between microalgal cell density and total bacteria in the first three culture volumes and a low correlation (0.27; p = 0.34) at 400-L column. The highest mean concentration of total bacteria (884.13 × 10 5 cells·mL -1 ) during the five days occurred at 18-L Carboy. The concentration of total bacteria at all levels was always higher than that of heterotrophic bacteria. The average ratio of heterotrophic to total bacteria was higher in the 2-L (0.0108) and 18-L (0.0172) cultures. The high biomass of C. muelleri and the presence of Vibrio spp. at the 18-L and 400-L levels indicate that it is necessary to establish programs to prevent diseases and economic losses caused by pathogenic bacteria in penaeid shrimp farming.