Variation of geosmin content in Anabaena cells and its relation to nitrogen utilization

The role of algae and cyanobacteria in the production and release of odorants in water

This review covers literatures pertaining to algal and cyanobacterial odor problems that have been published over the last five decades. Proper evaluation of algal and cyanobacterial odors may help establish removal strategies for hazardous metabolites while enhancing the recyclability of water. A bloom of microalgae is a sign of an anthropogenic disturbance in aquatic systems and can lead to diverse changes in ecosystems along with increased production of odorants. In general, because algal and cyanobacterial odors vary in chemistry and intensity according to blooming pattern, it is necessary to learn more about the related factors and processes (e.g., changes due to differences in taxa). This necessitates systematic and transdisciplinary approaches that require the cooperation of chemists, biologists, engineers, and policy makers.

Geosmin as a source of the earthy-musty smell in fruits, vegetables and water: Origins, impact on foods and water, and review of the removing techniques

The earthy-musty smell produced by Streptomyces sp. is assigned to geosmin and is responsible for the major organoleptic defects found in drinking water, fruits and vegetables such as grapes, mushrooms, carrots, and beet. Geosmin is also found in juices and musts before fermentation and its presence has been associated with partial presence of Botrytis cinerea. It has a variable detection threshold depending on the matrix and the detection level ranges from 5 to 50 ng/L. On the sensory level, very few individuals are immune to geosmin and although the intensity of the defect caused by this molecule decreases rapidly in the nose, a bad taste is very persistent in the mouth. As the origin of geosmin is fungal, conventional control techniques used for geosmin prevention are limited to ventilation, improving the integrity of plants and use of storage temperatures around 1 °C in a humidity-controlled environment. However, it has been demonstrated that only the combination of different prophylactic and preventive measures provide a relatively sufficient efficacy. Therefore, prevention of factors favoring the formation of geosmin is still topical. Some chemical treatments showed relatively good results against Botrytis cinerea. However, there is a requirement that must be met, namely that only one chemical per family per year must be used. Moreover, a multi-year alternation of chemical families is a strong agronomic recommendation. Regarding Penicillium, no active material is 100% approved and it negative effects plants such as beet and grapes. Consequently, the importance of finding effective ways to fight against geosmin formation is still relevant. From analytical point of view, measurement of geosmin is mainly based on gas chromatography.

Biochemistry and genetics of taste- and odor-producing cyanobacteria

Cyanobacteria are one of the principal sources of volatile organic compounds (VOCs) which cause offensive taste and odor (T&O) in drinking and recreational water, fish, shellfish and other seafood. Although non-toxic to humans, these T&O compounds severely undermine public trust in these commodities, resulting in substantial costs in treatment, and lost revenue to drinking water, aquaculture, food and beverage and tourist/hospitality industries. Mitigation and control have been hindered by the complexity of the communities and processes which produce and modify T&O events, making it difficult to source-track the major producer(s) and the factors governing VOC production and fate. Over the past decade, however, advances in bioinformatics, enzymology, and applied detection technologies have greatly enhanced our understanding of the pathways, the enzymes and the genetic coding for some of the most problematic VOCs produced by cyanobacteria. This has led to the development of tools for rapid and sensitive detection and monitoring for the VOC production at source, and provided the basis for further diagnostics of endogenous and exogenous controls. This review provides an overview of current knowledge of the major cyanobacterial VOCs, the producers, the biochemistry and the genetics and highlight the current applications and further research needs in this area.

Impact of the Botrytis cinerea strain and metabolism on (−)-geosmin production by Penicillium expansum in grape juice

Geosmin, an off-flavour of some rotten grapes, has been implicated in wine defects. Botrytis cinerea and Penicillium expansum were the most common among the numerous microorganisms isolated from rotten grapes. P. expansum produces geosmin on model media but not healthy grape juice. However, geosmin synthesis by P. expansum was demonstrated in grape juice and on crushed grapes that had been pre-cultured with certain B. cinerea strains. 34 out of 156 B. cinerea strains ([bot +] phenotype) isolated from the centre of grape bunches were able to induce high geosmin production, up to 494 ng/l, by P. expansum in grape juice. A study of the impact of grape juice composition on geosmin synthesis by P. expansum revealed the importance of nitrogen composition, particularly amino-acid deficiency. Metabolism of amino acids by B. cinerea was shown to be favourable to geosmin synthesis by P. expansum. However, the amino-acid and ammonium concentrations in grape juices pre-cultured with B. cinerea [bot -] and [bot +] strains were very similar implying that other factors are involved as well. Indeed, an ethanol-precipitable fraction, probably a polysaccharide, synthesized by B. cinerea [bot -], but not [bot +] strains, inhibited geosmin production by P. expansum.

Assessment of the effect of azo dye RP2B on the growth of a nitrogen fixing cyanobacterium--Anabaena sp

Certain nitrogen fixing cyanobacteria are diazotrophic, which profoundly impacts the aquatic ecosystem chemically and biologically. Although certain types are banned due to their carcinogenicity, azo dyes are commonly used in the dyeing or textile industry. This work investigates the effect of azo dye on the growth of cyanobacteria. Anabaena sp. isolated from the Da Jia Brook is an odor producing, nitrogen fixing cyanobacterium. The growth rates of Anabaena sp. in the media with or without nitrogen source were 3.56 x 10(-2) mg/ml day and 2.44 x 10(-2) mg/ml day, respectively. Anabaena sp. could not use azo dye RP2B as the nitrogen source. Experimental results indicated that the growth of Anabaena sp. was inhibited in the medium containing RP2B. The degree of inhibition increased from 50% to 81% with an increasing concentration of RP2B (0-50 mg/l). The IC-50 (inhibitory concentration) of RP2B on the growth of Anabaena sp. was 5 mg/l (as based on dry weight) or 7 mg/l (as measured by chlorophyll a).