Introduction

One potential commercial application of microalgae derived compounds that has, as yet, received little attention is the area of pharmaceuticals, antibiotics and other biologically active compounds. Both cell extracts and extracts of the growth media of various unicellular algae (e.g. Chlorella vulgaris, Chlamydomonas pyrenoidosa) have been proved to have antibacterial activity in vitro against both Gram-positive and Gram-negative bacteria. It has also been reported that a wide range of in vitro active antifungal activities are obtained from extracts of green algae, diatoms and dinoflagellates. Microalgae, such as Ochromonas sp., Prymnesium parvum, and a number of blue-green algae produce toxins that may have potential pharmaceutical applications (Borowitzka and Borowitzka, 1992).

Biologically active substances were proved to be extracted by microalgae. Various strains of cyanobacteria are known to produce intracellular and extracellular metabolites with diverse biological activities such as antialgal, antibacterial, antifungal and antiviral activity. Temperature of incubation, pH of the culture medium, incubation period, medium constituents and light intensity are the important factors influencing antimicrobial agent production (Noaman et al., 2004).

It is the main objective of this study to test 10 microalgae isolated from various freshwater reservoirs situated in Turkey for their antimicrobial activities on various microorganisms and optimize the conditions for the production of an antimicrobial agent by microalgae.

Materials And Methods

Culturing and growth conditions

Test organisms

Dry weight determination

Preparation of the extracts

Inhibitory effect by the agar-well diffusion method

Statistical analysis

Results And Discussion

A large number of microalgal extracts and extracellular products have been found to have antibacterial activity. However, pH of the medium, incubation period and temperature of incubation were very important for the biosynthesis of antimicrobial agent products as secondary metabolites. Noaman et al., (2004) have reported that temperature 35 °C, pH 8 and 15 days of incubation were the best for growth and antimicrobial agent production. In this study, these were chosen as an optimum pH, incubation periods and temperature.

The present study is an endeavor towards antimicrobial agent production by some microalgae has screened for its biological activity against different species of bacteria and fungi and it was found that it has high biological activity against Bacillus subtilis ATCC 6633, Bacillus thuringiensis RSKK 380, Bacillus megaterium RSKK 578, Escherichia coli ATCC 11230, Pseudomonas aeruginosa ATCC 29212, Candida tropicalis and Saccharomyces cerevisiae.

Antibacterial and antifungal activity of microalgae (Chrococcus sp. Mogan, Chrococcus sp. Kurtbo?azi, Oscillatoria sp. ?.F., Oscillatoria sp. Burdur, Oscillatoria sp. Mogan, Oscillatoria limnosa 1966/1380, Anabaena sp. Burdur, Synechocystis aquatilis 1965/426, Chlorella vulgaris) against test microorganisms were shown in Table 1. The antimicrobial activity of test microorganisms against antibiotics and fungicides were shown in Table 2.

Figure 1

Table 1: Antimicrobial activity of extracts obtained from microalgae

Figure 2

Table 2: Diameters of inhibition zone (mm) exhibited against test microorganisms of standard antibiotics and fungicides.

As the results reveal, while acetone and ether extracts exhibit antimicrobial activity on gram negative bacteria; methanol extracts exhibit that activity on Gram-positive bacteria. On the other hand, ethanol extracts exhibited antimicrobial activity on both Gram-positive and Gram-negative organisms. Yet, the chloroform extracts did not exhibit antimicrobial activity. Oscillatoria sp. ve Chrococcus sp. exhibited antifungal activity on yeasts. The methanol extract, obtained from Oscillatoria sp. Mogan, showed antifungal activity on S. cerevisae and S. cerevisae 2SI TP (3-2).

In general, activities both against Gram-negative and Gram-positive bacteria in ethanol extracts were observed. The only activity against C. tropicalis was found also in ethanol extracts obtained from Chrococcus sp. Kurtbo?azi. An activity was determined in acetone and ether extract only against P. aeruginosa ATCC 29212. No activity was determined in chloroform extract against test bacteria. However, the microalgae differ significantly in their activity against test microorganisms (F=1.123; df:10, p<0.05).

When the effects of extracts obtained from microalgae were compared with the antibiotics used in the study, ether and acetone extracts obtained from Chrococcus sp. Mogan, ether and acetone extracts obtained from Oscillatoria sp. (?.F.) and ethanol extract obtained from Oscillatoria sp. Mogan (Table 1) exhibited antibacterial activity on Pseudomonas aeroginosa ATCC 29212. Ethanol extract obtained from Anabaena sp. (Burdur) exhibited antibacterial activity on B. megaterium RSKK 578 and B. thuringiensis RSKK 380. In this study, the antimicrobial activity of microalgae could be explained by the presence of cyclic peptides, alkaloids and lipopolysaccharides.

Both cell extracts and extracts of the growth media of various unicellular algae have been proved to have antibacterial activity in vitro against both Gram-positive and Gram-negative bacteria. Microalgae such as Ochromonas sp., Prymnesium parvum, and a number of blue green algae produce toxins that may have potential pharmaceutical applications (Borowitzka, 1995).

There are a number of reports by many authors on antibiotic and other pharmacological effects from cyanobacteria. The genius from cyanobacteria, generally studied on an antimicrobial activity are Nostoc sp.(Knübel et al., 1990; Bloor and Englan, 1991; de Mule et al., 1991), Scytonema sp.(Chetsumon et al., 1993; 1994; 1995; Stewart et al., 1988; Ishida et al., 1997), Microcystis sp.(Carmichael et al., 1988), Oscillatoria sp. (Bagchi et al., 1990; Barchi et al., 1984) and Phormidium sp. (Fish and Codd, 1994).

The extracts of 12 cyanobacterial strains were investigated for their antibiotic activities against 7 microorganisms by Kreitlow et al. (1999). All cyanobacterial samples, extracts from 7 species were concluded to inhibit the growth of at least one of the Gram-positive bacteria Micrococcus flavus, Staphylococcus aureus and Bacillus subtilis. Finally, the hexane and dichloromethane extracts were shown to exhibit antimicrobial effects.

Bagchi et al. (1990) originally proposed that natural algaecides could effectively be applied in control of toxic algal blooms.

de Mule et al. (1991) determined that the methanol extracts of Nostoc muscorum revealed antibacterial activity on Sclerotinia sclerotiorum. Ishida et al. (1997) observed that kawaguchipeptin B, isolated from Microcystis aeruginosa and inhibited the growth of Staphylococcus aureus. It was observed that thermo tolerant cyanobacterium Phormidium sp. inhibited the growth of Staphylococcus aureus and Candida albicans (Fish and Codd, 1994). Barchi et al. (1984) found out that liphophilic extracts of Oscillatoria accutissima were anti-neoplastic and toxic activities. Özdemir et al. (2001) synthesized found that the Spirulina extracts, obtained from various solvents exhibited antimicrobial activity on both Gram-positive and Gram-negative organisms.

As is in the studies reported, it was observed that the extracts obtained from various solvents used in this study had antibacterial and antifungal activities, and that these extracts could be much more effective when compared with contemporary antibiotics and fungicides.