Antibacterial and Antifungal Properties of Some Marine Diatoms in Culture

Fifteen diatoms including 11 Chaetoceros species were tested against gram + , gram— terrestrial bacterial, marine bacteria, human pathogenic fungi (yeasts, moulds, dermatophytes) and phytofungi from Mediterranean plants. Nine diatoms were found to be significantly active against both bacteria and fungi. Chaetoceros lauderi was strongly active against the dermatophyte Microsporum gypseum and against 3 phytofungi from the genus Fusarium. Introduction It is only recently that marine planktonic algae have been recognized äs potential sources of antibacterial and antifungal substances. Antibacterial äctivity has been often detected and reported (Steemann-Nielsen 1955, Duff et al. 1956, Burkholder et al 1960, Aubert et al. 1968, Ramamurthy 1970, Berland et al. 1972, Cooper et al. 1983, Findlay and Patil 1984). Reports of the screening of marine planktonic algae for their antifungal äctivity are few. Antifungal äctivity has been found either in intact cells or in algal extracts. The homogenate of Lyngbia majuscula (Cyanophyceae) was active on Penicillium sp. , Candida albicans and Cryptococcus neoformans (Welch 1962). The ether fraction of Goniodoma sp. , a dinoflagellate from Puerto-Rico, inhibited the growth of Candida albicans, Cryptococcus neoformans, Saccharomyces cerevisiae, Trichophyton mentagrophytes and some species of the genus Penicillium (Sharma et al 1962). Chloroform and water soluble fractions from Gambierdiscus toxicus (Dinoflagellate) were active on Trichophyton mentagrophytes and Sporothrix schenckii (Durand 1984). In a previous paper (Pesando et al. 1979 a) we screened 50 planktonic algae for antifungal properties and we found significant äctivity in the aqueous extracts of 5 diatoms, especially in the genus Chaetoceros (3 species). In the present study whole cells of 15 marine diatoms including 11 species of Chaetoceros were tested against marine and terrestrial bacteria, human pathogenic fungi and phytofungi. Material and Methods Algal samples The marine diatoms listed in Table I were cultivated in 51 batches at 18°C under continuous light of 95 W m~ in Provasoli medium (Provasoli 1966), with addition of sodium metasilicate (2 mg/ml). Four litres of each diatom culture in the early stationary phase were filtered onto Sartorius membranes (diameter 142 mm, 8 porosity) and patches of 10 to 12 mm covered with cells were used for the bioassay. After incubation the Inhibition zone Z was measured äs shown in Figure 1. Botanica Marina / Vol. 30 / 1987 / Fase, l Copyright © 1987 Walter de Gruyter · Berlin · New York 42 Viso et aL: Antibacterial and antifungal activities of marine diatoms in culture Table L Marine diatoms studied. Asterionella glacialis Castr. SME Chaeioceros affinis Lauder SMS Chaetoceros brevis Schutt CERBOM Chaetoceros diadema (Ehrenberg) Gran SME Chaetoceros pseudocurvisetus Mangin SME Chaetoceros danicus Cleve SMS Chaetoceros dldymus Ehrenberg SME Chaetoceros lauderi Ralfs in Lauder SMV Chaetoceros protuberans Lauder . CERBOM Chaetoceros socialis Lauder CERBOM Chaetoceros simplex Ostenfeld CERBOM Chaetoceros septentrionalis Oestrup U. N. Fragilaria pinnata Ehrenberg SME Rhizosolenia sp. SMV Thalassiosira sp. SMV CERBOM: Centre d'Etude et de Recherche de Biologie et dOceanographie Medicale, Nice, France. SME: Station Marine d'Endoume, Marseille, France. SMSi Station Marine de la Spezia. Italic. SMV: Station Marine de Villefranche-sur-Mer, France. U. N. : Universite de Nantes, France. Antimicrobial testing Microbial assays were carried out by the diffusion technique in Petri dishes (Chabbert 1963) on a wide variety of microorganisms. When the planktonic cells Bacteria or fungi . ^y£>^ ^ί Filter eovered with cell diatoms Z 2 2 Z ; Fig. 1. Inhibition zone (Z) on microorganisms tested. were transferred from saline culture medium to hypotonic agar prepared with distilled water, active products were liberated due to osmotic shock. Seven terrestrial gram+ and gram— bacteria and 8 pathogenic fungi representative of different types of human disease were tested. Inhibition tests were also performed on 9 marine bacteria to evaluate the ecological impact in the natural environment and on 8 phytofungi responsible for diseases of Mediterranean plants. Incubation conditions depended upon the test-microorganism. Bacteria were incubated for 18h, terrestrial Table II. Inhibition of terrestrial bacterial growth by diatom cells. Width of Inhibition zone: — no activity Z = 0 + + + 12 mm < Z < 24 mm + 0 < Z < 4 mm + -f + + Z > 24 mm + + 4 mm < Z < 12 mm U Unknown IPC: Institut Pasteur Collection Diatoms Gram — Gram + ci 'C £ts u IX o cu 'S lS* Uex 8 •5 uCu 1 N cell ml" in diatom cultures 2 ^§ υ Q-,