Research Product

The determination of biomass and community structure of the fungal community in estuarine detritus by cultural or extractive methods can be incomplete and selective. Biochemical measures could provide a less biased estimate of the fungal components if they can be proved reliable. Assay of lipid and cell wall components can readily provide differentiation in reciprocal mixtures of bacteria and fungal monocultures. To test natural microbial assemblies, small plastic sheets were exposed in a subtropical estuary. The sheets were then transferred to a laboratory where estuarine environments that inhibit prokaryotic growth and stimulated fungal growth were compared with an environment where eukaryotic growth was inhibited and prokaryotic growth was stimulated. The morphology determined by scanning electron microscopy showed typical mycelial networks where eukaryotic growth was stimulated and none where inhibited. The stimulation of eukaryotic growth produced a greater biomass measured in terms of lipid phosphate, respiratory activity or extractable adenosine nucleotides, but with a slower synthesis of phospholipids and DNA and a smaller concentration on muramaic acid (a unique prokaryote wall component). The stimulation of eukaryotic growth increased the rate of sulpholipid synthesis relative to DNA or phospholipid synthesis. The prokaryote-stimulated environment yielded much higher proportions of iso and anteiso pentadecanoic, cis vaccenic, 17 and 19 carbon cyclopropane fatty acids in the lipids. The eukaryotic-stimulated environment showed increased 18 carbon dienoic, polyenoics of both the y and x linolenic series and the long (greater than 22 carbon) fatty acids. The prokaryote-stimulated environment showed significantly higher levels of lipid ribose, arabinose, xylose, glucose and several unknown neutral carbohydrates compared with much elevated lipid inositol in the eukaryote-stimulated environment. The prokaryote-stimulated environment yielded a lipid extract rich in ethanolamine and lysine; the eukaryote-stimulated environment yielded lipid enriched in serine. The steriods as expected were predominant in the eukaryote-stimulated microflora. Two estuarine fungi grown in monoculture showed similar lipid profiles to the eukaryota-stimulated microcosm, suggesting the biochemical measures initiated in this study can lead to a deeper understanding of the role of fungi in marine microbial ecosystems.