Makridis, P., Institute of Aquaculture, Hellenic Center for Marine Research, P.O. Box 2214, 71003 Iraklio, Crete, Greece, Biology Department, University of Patras, Rio 26500, Patras, Greece
Ferreira, T., Universidade do Algarve, Campus de Gambelas, Faro, Portugal
Kokou, F., University of Crete, Department of Biology, Greece
Tsigenopoulos, C.S., Institute of Marine Biology and Genetics, Hellenic Center for Marine Research, P.O. Box 2214, 71003 Iraklio, Crete, Greece
Divanach, P., Institute of Aquaculture, Hellenic Center for Marine Research, P.O. Box 2214, 71003 Iraklio, Crete, Greece

Microbiological conditions in 200 L cultures of microalgae Chlorella minutissima in polyethylene sleeves were examined. The influence of addition of antibiotic (nitrofurantoin) was studied. Samples were taken 2, 5, 9, and 14 d after inoculation and were spread on solid Zobell medium and on thiosulfate citrate bile salts sucrose agar for the enumeration of total numbers of bacteria and numbers of presumptive Vibrio bacteria, respectively. Microalgae grew well in the cultures and high numbers of culturable bacteria (about 107 bacteria/mL) were present in all microalgae cultures. Addition of antibiotic in 200-L cultures of C. minutissima did not result in a significant decrease of total counts of bacteria per unit volume (P > 0.05), while the numbers of presumptive Vibrio were higher in cultures added antibiotic compared with the control treatment (P < 0.05). The numbers of presumptive Vibrio per unit volume and the percentage of fast-growing bacteria were higher in microalgae supernatant than in noncentrifuged samples. Representative colonies were taken from all samples and in total 649 bacterial strains were isolated during this study. A range of phylotypes was identified by amplification and sequencing of the 16S rDNA gene and phylogenetic trees were constructed. Several members of the Roseobacter clade were dominant among the culturable isolates. © Copyright by the World Aquaculture Society 2012.