Can fungi compete with marine sources for chitosan production?

Chitosan, a ß-1,4-linked glucosamine polymer is formed by deacetylation of chitin. It has a wide range of applications from agriculture to human health care products. Chitosan is commercially produced from shellfish, shrimp waste, crab and lobster processing using strong alkalis at high temperatures for long time periods. The production of chitin and chitosan from fungal sources has gained increased attention in recent years due to potential advantages in terms of homogenous polymer length, high degree of deacetylation and solubility over the current marine source. Zygomycetous fungi such as Absidia coerulea, Benjaminiella poitrasii, Cunninghamella elegans, Gongrenella butleri, Mucor rouxii, Mucor racemosus and Rhizopus oryzae have been studied extensively. Isolation of chitosan are reported from few edible basidiomycetous fungi like Agaricus bisporus, Lentinula edodes and Pleurotus sajor-caju. Other organisms from mycotech industries explored for chitosan production are Aspergillus niger, Penicillium chrysogenum, Saccharomyces cerevisiae and other wine yeasts. Number of aspects such as value addition to the existing applications of fungi, utilization of waste from agriculture sector, and issues and challenges for the production of fungal chitosan to compete with existing sources, metabolic engineering and novel applications have been discussed to adjudge the potential of fungal sources for commercial chitosan production.

Flocculation of dimorphic yeast Benjaminiella poitrasii is altered by modulation of NAD-glutamate dehydrogenase.

A strategy to control flocculation is investigated using dimorphic yeast, Benjaminiella poitrasii as a model. Parent form of this yeast (Y) exhibited faster flocculation (11.1 min) than the monomorphic yeast form mutant Y-5 (12.6 min). Atomic force microscopy revealed higher surface roughness of Y (439.34 rms) than Y-5 (52 rms). Also, the former had a zeta potential of -65.97+/-3.45 as against -50.21+/-2.49 for the latter. Flocculation of both Y and Y-5 could be altered by supplementing either substrates or inhibitor of NAD-glutamate dehydrogenase (NAD-GDH) in the growth media. The rate of flocculation was promoted by alpha-ketoglutarate or isophthalic acid and decelerated by glutamate with a statistically significant inverse correlation to corresponding NAD-GDH levels. These interesting findings open up new possibilities of using NAD-GDH modulating agents to control flocculation in fermentations for easier downstream processing.

Fungal spore germination into yeast or mycelium: possible implications of dimorphism in evolution and human pathogenesis.

The ability of dimorphism in fungi is conventionally regarded as a reversible change between the two vegetative forms, yeast and mycelium, in response to environmental change. A zygomycetous isolate, Benjaminiella poitrasii, exhibited yeast-mycelium transition in response to the change in temperature (37-28 degrees C) and decrease in glucose concentration. For the first time the presence of dimorphic response during asexual and sexual spore germination is reported under the dimorphism-triggering conditions in B. poitrasii. The zygospores germinated into budding yeast when subjected to yeast-form supporting conditions. The mycelium-form favoring conditions gave rise to true mycelium. Similarly, the asexual spores displayed a dimorphic response during germination. Our observations suggest that dimorphism is an intrinsic ability present in the vegetative, asexual, and sexual forms of the fungus. As dimorphic fungi are intermediate to the unicellular yeast and the filamentous forms, understanding of the dimorphic character could be useful to trace the evolutionary relationships among taxonomically different fungi. Moreover, the implications of spore germination during the onset of pathogenesis and in drug development for human health care are discussed.

Chitinolytic enzymes: an exploration.

Chitin and chitinolytic enzymes are gaining importance for their biotechnological applications. Particularly, chitinases are used in agriculture to control plant pathogens. Chitinases and chitooligomers produced by enzymatic hydrolysis of chitin can also be used in human health care. The success in employing chitinases for different aspects depends on the supply of highly active preparations at reasonable cost. Therefore, the understanding of biochemistry and genetics of chitinolytic enzymes, their phylogenetic relationships and methods of estimation will make them more useful in a variety of processes in near future.

Dimorphism in Benjaminiella poitrasii: involvement of intracellular endochitinase and N-acetylglucosaminidase activities in the yeast-mycelium transition.

The chitinase and N-acetylglucosaminidase activities in cell-wall-bound and free fractions in the dimorphic fungus Benjaminiella poitrasii were studied as a function of morphological (unicellular yeast-mycelium) transition. The specific activities of chitinases of cell-wall-free, particularly in the membrane fraction, were significantly different in the yeast and mycelial forms. During the yeast-mycelium transition, the N-acetylglucosaminidase activity isolated in a membrane preparation increased steadily. The activity of the yeast cells (0.83 +/- 0.17 nkat/mg protein) increased 17-fold to 14.2 +/- 1.7 nkat/mg protein in 1-d-old mycelial cells. The endochitinase activity increased 12-fold between 6 and 12 h and thereafter practically remained unchanged up to 24 h. A reverse trend in the chitinolytic activities was observed during the mycelium-yeast transition. Isoelectrofocussing (pH range 3.5-10) of mixed membrane fraction free of particulate fraction of parent and morphological (Y-5, yeast-form) mutant cells separated endochitinase and N-acetylglucosaminidase activity into two pH ranges, viz. 4.3-5.7 and 6.1-7.7, respectively. The predominant N-acetylglucosaminidase activity observed at pH 6.9 and 7.1 for the parent strain membrane fraction was undetected in the mutant preparation. The results suggested that the membrane-bound (either tightly or loosely) chitinolytic enzymes, particularly, N-acetylglucosaminidase, significantly contributed to the morphological changes in B. poitrasii.