In Vitro CuIture of the Tropical Sponge Axinella corrugata (Demospongiae): Effect of Food Cell Concentration on Growth, Clearance Rate, and Biosynthesis of Stevensine

Abstract

In vitro culture is one possible method for supplying sponge metabolites for pharmaceutical applications, but appropriate feeding regimens that maximize both growth and metabolite biosynthesis are largely unknown. According to the natural concentration (NC) of cells 1 to 50 µm in size that are available to wild Axinella corrugata, we fed explants a multispecific diet of bacteria, microalgae, and yeast at 4 different concentrations: 1NC, 3NC, 5NC, and 5+1NC (the last consisted of 5 NC of bacteria and 1 NC of microalgae and yeast). Explants fed a 3NC diet had the best culture response, growing on average from 8.5 g to 10.3 g in 8 weeks, and showing a 110% increase in concentration (milligrams per gram of dry weight) of the antitumor compound stevensine. Stevensine production in 3NC explants, representing the total milligrams of metabolite per explant, increased by 157% over the study. Explants fed at 1NC had relatively stable weights, indicating that the diet met metabolic costs only. Explants fed at the two highest concentrations lost weight after 4 weeks, possibly because long-term high cell concentration blocked their aquiferous system, reducing their ability to feed efficiently. Stevensine production in explants fed the 1NC, 5NC, or 5+1NC diets were similar, and varied little from the initial amount. A separate experiment showed that the clearance rate for A. corrugata is similar between the examined food types and cell concentrations over 5 hours, averaging 766 ml h⁻¹ g DW⁻¹.Overall, this study demonstrates that relatively small changes in food abundance can greatly affect both sponge growth and metabolite biosynthesis. The good growth and increased production of the target metabolite stevensine for A. corrugata explants fed a 3NC diet suggests that in vitro culture is a viable method of supplying some sponge metabolites.