Antibacterial activity of the extracts of the Seaweed Galaxauramarginata (Rhodophyta, Nemaliales)

Rozas E., Freitas, J. C.

Department of Physiology of Biosciences Institute, University of São Paulo, São Paulo, SP, Brazil.

Anti-bacterial and haemolytic activities of substances extracted from Galaxaura marginata (J.V. Lamouroux) were investigated using seaweed collected at São Sebastião channel (45^o25’ W, 26^o49’ S), SP, Brazil. Samples, collected in each season, were homogenized in ethanol:acetic acid (5:1 v/v) and  partitioned with hexane, obtaining the apolar fractions (H1 and H2) and polar fractions (H3 and H4). The polar fractions were filtered through membranes of 3000 and 1000 Da cut off. All fractions were tested for haemolytic activity in mouse erythrocytes and anti-bacterial activity in several Vibrio strains (Cp1: V. Anguillarum, CM3: V. damsela,  F9: V. Anguillarum-Like) both in solid and liquid media. Apolar fractions and the polar fraction H3 induced haemolysis (EC₅₀, IC₉₅: 0,38, 0.36-0.39 (H1), 0.47, 0.42-0.52 (H2), 2.95, 2.69-3.25 (H3) mg/mL), but did not show anti-bacterial activity. In contrast, the polar fraction H4 of each season, in concentrations ranging from 1 to 10 mg/mL, exhibited inhibitory or stimulatory effects on the bacterial growth, depending on the concentration used,  but even at the highest concentration tested, their haemolytic activity was inferior to the 35%. The “summer fraction” showed the strongest anti-bacterial activity in all three strains( 91±0,9 %, CM3, 96,9± 0,5 % CP1, 94.36±0,9 % F9) and the winter fraction the weakest activity (21,6±1,9 %, CM3, 49,4± 2.1 % CP1, 78,4 ±1,9 % F9). The latter, in  the lowest four concentrations, showed stimulating activity in the growth of CP1 (55,37 % over the control).  This fraction also stimulated the growth of V. damsela, an effect also shown by the fall fraction in F9. Differential filtering of H4 showed that only compounds with molecular weights between 3 and 1 KD had antibacterial activity.

In conclusion, G. marginata has polar substances that regulate bacterial growth, stimulating or inhibiting it in a season-dependent manner.

Key words: Galaxaura, anti-bacterial, haemolytic, stimulatory.

CORRESPONDENCE TO:

Enrique Eduardo Rozas Sánchez, Rua Corinto, 92, São Paulo, SP, CEP: 05586-001, Brasil, Email: enrique.sanchez@eudoramail.com