Evidence for inhibition of bacterial luminescence by allelochemicals from Fibrocapsa japonica (Raphidophyceae), and the role of light and microalgal growth rate

The marine microalga Fibrocapsa japonica Toriumi and Takano (Raphidophyceae) produces haemolysins, neurotoxins and reactive oxygen species (ROS). To quantify potential effects of such bioactive compounds on surrounding organisms the marine bacterium Vibrio fischeri was exposed to F. japonica culture samples. Inhibition of V. fischeri 's natural luminescence, indicative of impaired metabolism, was related to the number of F. japonica cells added. The effect was fast, within 15 min. It was caused by one, possibly several, excreted substances that were less active after heating. Freezing of culture supernatant partly inactivated these substances, but ROS-scavenging enzymes had no effect. Light enhanced the V. fischeri luminescence inhibition in two ways. The direct effect of light on the action of F. japonica luminescence inhibiter(s) could be described by a saturation curve with maximum effect above 20 mu mol photons m(-2) s(-1). Light also had an indirect effect: biomass production, dependent on light availability, was closely related to the amount of inhibiting compound(s) produced by the alga. Algal growth rate, rather than its cell density, determined the bacterial luminescence inhibition per F. japonica cell, resulting in a 5-fold stronger inhibition at maximum growth rates compared to cells that barely grew during the stationary growth phase. The bioassay with F. japonica and V. fischeri has allowed quantification of the negative effects on bacteria in the microalgal microenvironment. The results presented here suggest that at favourable growth conditions F. japonica releases bioactive compounds that improve its competitive abilities

Haemolytic activity of live Phaeocystis pouchetii during mesocosm blooms

Chemical defence is a potential mechanism contributing to the success of Phaeocystis species that repeatedly dominate the phytoplankton in coastal areas. Species within the genus Phaeocystis have long been suspected of imposing negative effects on co-occurring organisms. Recently a number of toxins have been extracted and identified from Phaeocystis samples, but it is not clear if they do enhance the competitive advantage of Phaeocystis species. In the present study the cytotoxic impact of live Phaeocystis pouchetii to human blood cells in close proximity, regardless of the nature of the responsible mechanism, was quantified using a bioassay. Haemolytic activity was measured during blooms of P. pouchetii in mesocosms. These environments were chosen to mimic natural conditions including chemically mediated interactions that could trigger defensive and/or allelopathic responses of Phaeocystis. Haemolytic activity correlated with P. pouchetii numbers and was absent during the preceding diatom bloom. Samples containing live P. pouchetii cells showed the highest activity, while filtered sea water and cell extracts were less haemolytic or without effect. Dose-response curves were linear up to 70% lysis, and haemolysis in samples containing live P. pouchetii cells reached EC50 values comparable to known toxic prymnesiophytes (1.9 * 10(7) cells l(-1)). Haemolytic activity was enhanced by increased temperature and light. The results indicate that unprotected and thus presumably vulnerable cells present in a P. pouchetii bloom may lyse within days

Carbohydrates in the North Sea during spring blooms of Phaeocystis: A specific fingerprint

info:eu-repo/semantics/publishe

Growth and production of the venerid bivalve Eurhomalea exalbida in the Beagle Channel, Tierra del Fuego

Growth, mortality and productivity of the hard clam E. exalbida from Ushuaia Bay, Beagle Channel were investigated. The parameters of the von Bertalanffy growth function were estimated to be H = 73.98 mm, K = 0.180 y 1, t0 = 0.147 y. Maximum individual production amounted to 2.742 g shell free wet mass (SFWM) at 49.5 mm shell height. Animals between 40 mm and 70 mm shell height contribute most to overall population somatic production P of 133.89 g SFWM m-2 y-1. Mean annual biomass B amounted to 1122.69 g SFWM m-2 y-1. Annual P/B ratio and mortality rate Z were estimated to 0.119 y-1 and 0.141 y-1, respectively. Slow growth and low turnover makes this population less suitable for sustainable commercial exploitation

Allelopathic effects of Alexandrium spp. on Prorocentrum donghaiense

Effects of toxic Alexandrium species on Prorocentrum donghaiense were studied in co-cultures and filtrates in order to shed some light on the competition between the co-occurring harmful algae. The three live cultures of Alexandrium tamarense and Alexandrium minutum negatively affected the growth of P. donghaiense, while only A. minutum was affected by P. donghaiense when they were in 1:3 ratio of cells. Each species was affected by the co-occurring algae as could be observed by microscopy. The allelopathic effects observed in co-culture did not correlate with the measured content of the intracellular PSP toxins but matched the observed hemolytic properties of the culture filtrates, suggesting that certain hemolytic substances other than PSP toxins are responsible for the allelopathic effect of Alexandrium. (C) 2010 Elsevier B.V. All rights reserved