In order to study fungal diversity in oxygen minimum zones of the Arabian Sea, we analyzed 1440 cloned small subunit rRNA gene (18S rRNA gene) sequen

A wealth of microbial eukaryotes is adapted to life in oxygen-deficient marine environments. Evidence is accumulating that some of these eukaryotes survive anoxia by employing dissimilatory nitrate reduction, a strategy that otherwise is widespread in prokaryotes. Here, we report on the anaerobic nitrate metabolism of the fungus Aspergillus terreus (isolate An-4) that was obtained from sediment in the seasonal oxygen minimum zone in the Arabian Sea, a globally important site of oceanic nitrogen loss and nitrous oxide emission. Axenic incubations of An-4 in the presence and absence of oxygen and nitrate revealed that this fungal isolate is capable of dissimilatory nitrate reduction to ammonium under anoxic conditions. A ¹⁵N-labeling experiment proved that An-4 produced and excreted ammonium through nitrate reduction at a rate of up to 175 nmol ¹⁵NH₄ ⁺ g^-1 protein h^-1. The products of dissimilatory nitrate reduction were ammonium (83%), nitrous oxide (15.5%), and nitrite (1.5%), while dinitrogen production was not observed. The process led to substantial cellular ATP production and biomass growth and also occurred when ammonium was added to suppress nitrate assimilation, stressing the dissimilatory nature of nitrate reduction. Interestingly, An-4 used intracellular nitrate stores (up to 6–8 μmol NO₃ ^- g^-1 protein) for dissimilatory nitrate reduction. Our findings expand the short list of microbial eukaryotes that store nitrate intracellularly and carry out dissimilatory nitrate reduction when oxygen is absent. In the currently spreading oxygen-deficient zones in the ocean, an as yet unexplored diversity of fungi may recycle nitrate to ammonium and nitrite, the substrates of the major nitrogen loss process anaerobic ammonium oxidation, and the potent greenhouse gas nitrous oxide.

Agricultural wastes have attractive potential as alternate energy sources. However, a major bottleneck is to identify eco-friendly treatment methodologies to utilize them. The large diversity of unexplored, novel, and potential microorganisms hold great promise and require periodic isolation and characterization of microorganisms for bioprospection. In this study, approximately 100 fungal isolates were tested for their lignocellulolytic enzyme activities, based on plate assay, followed by quantification of enzyme activity. From this, M2E (Inonotus tropicalis) and 2a (Cerrena unicolor) showed good growth and proficient ligninolytic activity; isolates GK1 (Chaetomium globosum) and GK2 (Chaetomium brasiliense) exhibited exceptional cellulolytic activity on lignocellulosic substrates such as rice straw and sugarcane bagasse. Consortia of the potential ligninolytic and cellulolytic isolates were set up to determine their ability to biodegrade the lignocellulosic substrates such as rice straw and sugarcane bagasse. The efficiency of the consortia was determined on the basis of the increase in enzyme activity; it was also evident through scanning electron microscopy, x-ray diffraction analysis of the degraded substrates, and the sugar yield. Experiments were also carried out to compare the biological with the physical pretreatment methods. The consortium of ligninolytic and cellulolytic marine-derived fungi developed in this study prove to have the potential for application in the effective utilization of agricultural wastes.