Effect of the blue pigment produced by the tropical diatom Haslea nusantara on marine organisms from different trophic levels and its bioactivity

Abstract

Marennine is the blue-green pigment produced by the temperate ubiquiste marine diatom Haslea ostrearia. This pigment is water-soluble and excreted in seawater during H. ostrearia growth and ageing. Previous studies demonstrated the adverse effects of H. ostrearia culture supernatant that contains marennine (Blue Water, BW) against marine organisms. In tropical waters in the Southern hemisphere, a new diatom species has recently been discovered, Haslea nusantara, which shares a peculiarity with H. ostrearia in producing a blue-green, marennine-like pigment. However, little is known about the characteristics of the marennine-like pigment from H. nusantara and its bioactivity. The present study aimed to determine spectral characteristics of BW from H. nusantara in comparison to BW containing marennine of H. ostrearia, using UV–vis spectrophotometry, and to investigate the effects of BWs from these two species on several marine organisms from different trophic levels including autotrophs (Isochrysis galbana) and heterotrophs (Artemia salina). Additionally, the antibacterial activities of these BWs were also evaluated on two bacterial pathogens that are relevant to aquaculture, Vibrio harveyi and Staphylococcus aureus. The results show that both BWs from H. ostrearia and H. nusantara at 0.5 μg mL−1 significantly reduce the growth of I. galbana. At similar range of concentration, toxicity tests reveal that the both BWs from blue Haslea species significantly increase mortality rate of A. salina to a different extent. Additionally, both BWs from H. nusantara and H. ostrearia can inhibit the growth of tested bacterial pathogens. This study provides new insight into the different toxicity in the bioactivity of pigments obtained from the two species of blue diatoms from the same genus. Our results also demonstrate the need to determine concentrations that optimize beneficial effects and critical concentrations not to be exceeded before considering the use of marennine as natural antibacterial agents in the field of aquaculture.