Effect of Associated Bacteria on the Growth and Toxicity of Alexandrium catenella

Abstract

Saprophytic bacteria in cultures of the marine dinoflagellate Alexandrium catenella were removed to assess their effect on growth and paralytic shellfish poisoning toxin production of this dinoflagellate. The actual axenic status was demonstrated by the lack of observable bacteria both immediately after treatment and following extended incubation in the absence of antibiotics. Bacteria were measured by counting CFU and also by epifluorescence microscopy and PCR amplification of bacterial 16S-23S spacer ribosomal DNA to detect noncultivable bacteria. Removal of bacteria did not have any effect on the growth of the dinoflagellate except for the inhibition of A. catenella disintegration after reaching the stationary phase. Toxicity was determined in dinoflagellate cell extracts by different methods: high-performance liquid chromatography (HPLC); an electrophysiological test called the Electrotest, which measures the inhibition of saxitoxin-sensitive Na ؉ channels expressed in a cell line; and a mouse bioassay, which measures the toxic effect on the whole mammal neuromuscular system. A lower toxicity of the dinoflagellates in axenic culture was observed by these three methods, though the difference was significant only by the mouse bioassay and HPLC methods. Altogether the results indicate that axenic cultures of A. catenella are able to produce toxin, though the total toxicity is probably diminished to about one-fifth of that in nonaxenic cultures.

Biochemical features of a <i>Protoceratium reticulatum</i> red tide in Chipana Bay (Northern Chile) in summer conditions

“…As red tides become a more frequent phenomenon not only on this coast (Uribe and Espejo, 2003) but all over the world (Masó and Garcés, 2006), the quality and quantity of sea food for human consumption must be monitored, especially in spring and summer, when algal blooms become more extended and frequent, with subsequent impacts for local fisheries. In the present paper we provide no evidence for the toxicity of the red tide (we suggest a potential danger), but we demonstrate that dinoflagellates may have an equivalent lipid content to diatoms in this upwelling system when algal concentrations are similar.…”

“…Red tides are common in these upwelling areas, especially on the coast and in summer conditions (Pitcher and Calder, 2000;Uribe and Espejo, 2003). In Chile and Perú, the coastal economy is based mostly on artisanal fisheries (Thatje et al, 2008), and red tides are a well known negative event for consumption of fish and shellfish that have accumulated phytoplankton toxins filtered from sea water (Masó and Garcés, 2006).…”

Morphological and physiological changes in Microcystis aeruginosa as a result of interactions with heterotrophic bacteria

“…On the other hand, the quantitative and qualitative differences in phytoplankton species composition may lead to pronounced differences in the bacterioplankton species composition (Pinhassi et al, 2004). Some bacteria may promote the growth of algae or live in symbiosis with them (Ferrier, Martin & Rooney-Varga, 2002;Uribe & Espejo, 2003), while others inhibit the growth of algae or exert algicidal activities (Lovejoy, Bowman & Hallegraeff, 1998;Lee et al, 2000).…”

Effect of multiple antibiotic treatments on a paralytic shellfish toxin-producing culture of the dinoflagellate Alexandrium minutum

“…Several studies have sought to clarify the relationship between toxin production and algal-associated bacteria in the dinoflagellate genus Alexandrium (Lu et al 2000, Hold et al 2001, Uribe et al 2003. However, it is difficult to compare studies because of variations in the treatment regimens used to render the algal cultures bacteria-free and the different methods used to assess the axenic status.…”

“…One approach to defining the role of algalassociated bacteria is to create a bacteria-free (axenic) culture and assess the impact on PST production. Methods for obtaining axenic cultures have included growth on solid culture media (Guillard & Keller 1984), antibiotic treatment, sometimes in combination with other antibacterial agents (Hunt & Mandoli 1992, Cottrel & Suttle 1993, and repeated washing of algal cells with or without the addition of antibiotics (Hoshaw & Rosowski 1973, Uribe & Espejo 2003. Although the antibiotic treatment method is potentially effective, difficulties are encountered because of the wide variety of bacterial species present, which are not necessarily amenable to removal by a single antibiotic.…”