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1. Seminar paper presentation PCM 400 Topic: CHEMISTRY OF GEOSMIN BY AMADU ALHAJI UMARU 20/08/03/1709 SUPERVISED BY DR. JAMES YAKUBU

2. Introduction The sense of smell evokes the strongest memory of all the senses and is largely based on the perception of volatile organic compounds (VOCs). While VOCs are part and parcel of our lives, we know very little about their biological function. One enigmatic experience is the feeling of well-being that is generated by a walk in the forest. That smell is caused by geosmin, a sesquiterpene discovered in 1965, whose name is derived from the Greek words ‘ gê ’—earth and ‘ osmḗ ’— odour . Geosmin is abundant in nature and mainly produced by actinobacteria and myxobacteria in soil, and by cyanobacteria in aquatic systems. Geosmin also occurs in ascomycete fungi in Basidiomycota in liverwort in mosses in maize where it serves as a possible attractant of the corn earworm Heliothis zea , and in the defence secretions of the polydesmid millipede Niponia nodulosa .

3. STRUCTURE OF GEOSMIN Figure 1: Chemical Structure of Geosmin

4. Sources of Geosmin

5. Geosmin in Aquatic Systems Cyanobacteria and Actinobacteria are often associated with geosmin production in aquatic. The marine bacterium Myxococcus fulvus , a Deltaproteobacterium, also possesses a geosmin synthase gene, although its ability to produce the compound remains to be verified Cyanobacteria.

6. Biological Role of Geosmin in Terrestrial Systems As an abundant chemical compound in soil, geosmin may have an important influence on terrestrial organisms. Recently, it was reported that geosmin acts as a warning signal that repels the bacterial predator Caenorhabditis elegans ( bacteriophagous nematode) and reduced contact between the worms and the geosmin-producing bacteria S. coelicolor ( Zaroubi et al., 2022). Geosmin itself was not toxic to C. elegans but reduced grazing on S. coelicolor . Geosmin and other terpenes may play a role in controlling the activity of protists, which are known predators of soil bacteria, including Streptomyces (Becher et al., 2020).

7. Effects of Geosmin The human olfactory system is extremely sensitive to geosmin and is able to detect it at concentrations as low as anywhere from 0.4 parts per billion to 5 parts per trillion. Geosmin is responsible for the muddy smell in many commercially important freshwater fish such as carp, catfish, and tilapia ( Freidig and Goldman, 2014).

8. Geosmin in Water and Food Contamination As mentioned above, geosmin acts as a pollutant of water, which is mainly associated with production by cyanobacteria, though Actinobacteria also contribute to its accumulation. A study performed in Italy throughout the four different seasons showed that cyanobacteria counts were highly correlated with the increased odor in spring and summer, while an increased count in Actinobacteria correlated to a higher odor in autumn and winter.

9. Conclusions Despite considerable research, the treatment and control of geosmin and 2-MIB are still hindered by common misconceptions about their biological and spatial origins and their storage and release by cells. In particular, ( i ) it is often assumed that planktonic or benthic aquatic cyanobacteria and streptomycetes are the major sources of these VOCs, while eukaryotes(e.g., fungi), and terrestrial and distribution system sources are disregarded; (ii) discrete cell-bound and dissolved VOC fractions respond very differently to treatment, and their relative proportions have major implications for data interpretation, yet these fractions are rarely considered and, furthermore, are incompletely measured by most current analytical methods;(iii) key physical and biological processes

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