Glycerol is a valuable raw material for the production of industrially useful metabolites. Among many promising applications for the use of glycerol is its bioconversion to high value-added compounds, such as 1,3-propanediol (1,3-PD), succinate, ethanol, propionate, and hydrogen, through microbial fermentation. Another method of waste material utilization is the application of crude glycerol in blends with other wastes (e.g., tomato waste hydrolysate). However, crude glycerol, a by-product of biodiesel production, has many impurities which can limit the yield of metabolites. In this mini-review we summarize the effects of crude glycerol impurities on various microbial fermentations and give an overview of the metabolites that can be synthesized by a number of prokaryotic and eukaryotic microorganisms when cultivated on glycerol.

Bacteria of the Clostridium genus are often described only as a biological threat and a foe of mankind. However, many of them have positive properties and thanks to them they may be used in many industry branches (e.g., in solvents and alcohol production, in medicine, and also in esthetic cosmetology). During the last 10 years interest in application of C. botulinum and C. tetani in medicine significantly increased. Currently, the structure and biochemical properties of neurotoxins produced by these bacterial species, as well as possibilities of application of such toxins as botulinum as a therapeutic factor in humans, are being intensely researched. The main aim of this article is to demonstrate that bacteria from Clostridium spp. are not only pathogens and the enemy of humanity but they also have many important beneficial properties which make them usable among many chemical, medical, and cosmetic applications.

Study presented here demonstrates the ability of three newly isolated strains, obtained from environmental probes (manure, bottom sediment, and food waste) and identified as Clostridium bifermentans, Clostridium butyricum, and Hafnia alvei, to synthesize 1,3-propanediol (1,3-PD), organic acids (such as lactic, acetic, fumaric, succinic, and butyric acids), and ethanol from glycerol. The production of 1,3-PD as well as the glycerol pathways in C. bifermentans and H. alvei cells have not been investigated and described yet by others. Moreover, there is no data in the available literature on the products of glycerol utilization by H. alvei and there is only some incoherent data (mainly from the first half of the twentieth century) about the ability of C. bifermentans to carry out glycerol degradation. Additionally, this study presents complete hypothetical glycerol pathways and the basic fermentation kinetic parameters (such as yield and productivity) for both strains as well as for the newly isolated C. butyricum strain.