Ecology of fungi in the denitrification zones of the Arabian Sea

Abstract

The microbial process, denitrification was considered to be an inherent character of a few specialized groups of bacteria. But recently, the involvement of micro-eukaryotes such as fungi and foraminiferans are reported (Takaya et al., 2002; Risgaard-Peterson et al., 2006). Studies from the oxygen depleted denitrifying zones have brought to light interesting and novel microbial diversity (Epstein & Lopez-Garcia, 2007; Lopez-Garcia & Moreira 2008). Environmental sequences retrieved from these regions also show that fungi are one of the major components in this ecosystem. But there is a lack of knowledge on the role of the specific groups, like fungi present in oxygen-depleted environments. In this study I have attempted to quantify the abundance of fungi, estimate the cultivable and uncultured diversity of fungi and measure the growth and activity of a few selected fungi under oxygen depleted conditions. Fungal abundance from the denitrification zones of the Arabian Sea was studied based on their Colony Forming Units, fungal biomass Carbon and bacterial biomass Carbon. Statistical analysis showed significant difference between seasons in the coastal station sediments, with changing DO levels which has an impact on the total microbial abundance (Jebaraj & Raghukumar, 2009). Culturable fungi were isolated from all the sampling locations irrespective of the DO levels. The diversity indices calculated showed that the overall diversity was low in comparison with the mangrove and coastal station. However, analysis of the fungal cultures based on the 18S rDNA sequence showed that two of the cultures (# 11 and # 87) were significantly divergent from any of the cultures described so far. Phylogenetic analysis of the environmental fungal phylotypes grouped many of the uncultured sequences obtained from this study into clusters with environmental sequences obtained from similar anoxic regions from across the globe (Jebaraj et al., 2010). Fungal cultures screened for their denitrification activity demonstrated their ability to grow and reduce nitrate under suboxic and anoxic conditions. From this study the fungal abundance, diversity and activity in oxygen depleted marine environments are reported for the first time, showing the ecological role of fungi in these regions. Further studies are required to precisely study the fungal contribution in these unique niches.