Aggregate formation in axenic and microbial co-inoculated batch cultures of Aulacoseira
granulata (Bacillariophyceae)
VIEIRA1, A.A.H., GIROLDO2, D. & ORTOLAN2, P.I.C.
1 Laboratório de Ficologia, Departamento de Botânica, Universidade Federal de São Carlos, Rodovia Washington Luis Km 235, 13565-905, São Carlos, SP, Brasil.
2Departamento de Ciências Morfobiológicas, Fundação Universidade Federal do Rio Grande, Avenida Italia, Km 8, 96201-900, Rio Grande, RS, Brasil.
ABSTRACT: Aggregate formation involving diatoms is a well-known process, especially in the marine environment. The aim of this paper was to observe natural aggregates formation in axenic and microbial co-inoculated cultures of the freshwater diatom Aulacoseira granulata. The growth of bacteria and A. granulata were also monitored, as were qualitative alterations in the composition of the extracellular polysaccharide (EPS) produced by A. granulata in both axenic and microbial co-inoculated cultures. Aggregates were naturally formed in both conditions and our results suggested that the aggregation process increased significantly in the presence of a microbial community from Barra Bonita Reservoir. A. granulata biomass formation also significantly increased along bacterial growth and the EPS composition found in the microbial co-inoculated cultures was different to that of the axenic cultures. Rhamnose proportion increased around 50 % in microbial co-inoculated cultures, probably due to bacterial activity, increasing the hydrophobic properties of the EPS. The aggregation increase in the microbial co-inoculated cultures was correlated to the enhancement of the EPS hydrophobic nature, as well as to the biomass increase of A. granulata.
Key-words: Aulacoseira granulata, aggregates, extracellular polysaccharide, microbial degradation, bacterial growth.