Antagonistic properties of Trichoderma viride on post harvest cassava root rot pathogens

The effective in vitro screening tests of Trichoderma viride for antagonism against post harvest pathogens of cassava roots (Manihot esculenta Crantz) rot together with its competitive andmycoparasitic abilities informs its selection as the most promising candidate for the biocontrol of post harvest cassava root rot pathogens. While the percentage germination of the spores were observed toincrease with increasing dilution of the culture filtrate (100, 50, 25, and 10% ) at a concentration of 20,000 spores/ml, the percentage rot recorded amongst the untreated cassava roots ranged from 4%(Rhizopus oryzae) to 44% (Aspergillus flavus). Treatment with the antagonist and the subsequent storage resulted in a remarkable reduction in the frequency of occurrence of the normal root surfacemycoflora and the pathogens over a 3 weeks storage period. Botryodiplodia theobromae and R. oryzae were isolated only in the first week of storage and at a frequency of 3 and 2% rot, respectively, aftertreatment whereas A. flavus and Fusarium solani persisted throughout the whole storage period with 2 and 3% rot on the third week, respectively. The observed results suggest that T. viride is root surfacecompetent and highly antagonistic

Cyanate as energy source for nitrifiers

Ammonia- and nitrite-oxidizers are collectively responsible for the aerobic oxidation of ammonia via nitrite to nitrate and play essential roles for the global biogeochemical nitrogen cycle. The physiology of these nitrifying microbes has been intensively studied since the first experiments of Sergei Winogradsky more than a century ago. Urea and ammonia are the only recognized energy sources that promote the aerobic growth of ammonia-oxidizing bacteria and archaea. Here we report the aerobic growth of a pure culture of the ammonia-oxidizing thaumarchaeote Nitrososphaera gargensis(1) on cyanate as the sole source of energy and reductant, the first organism known to do so. Cyanate, which is a potentially important source of reduced nitrogen in aquatic and terrestrial ecosystems(2), is converted to ammonium and CO(2) by this archaeon using a cyanase that is induced upon addition of this compound. Within the cyanase gene family, this cyanase is a member of a distinct clade that also contains cyanases of nitrite-oxidizing bacteria of the genus Nitrospira. We demonstrate by co-culture experiments that these nitrite-oxidizers supply ammonia-oxidizers lacking cyanase with ammonium from cyanate, which is fully nitrified by this consortium through reciprocal feeding. Screening of a comprehensive set of more than 3,000 publically available metagenomes from environmental samples revealed that cyanase-encoding genes clustering with the cyanases of these nitrifiers are widespread in the environment. Our results demonstrate an unexpected metabolic versatility of nitrifying microbes and suggest a previously unrecognized importance of cyanate for N-cycling in the environment