Phenol production in bacteria?

Phenol is an important commodity chemical because of its role as the precursor molecule for many widely used chemicals. Currently, phenol is produced from non-renewable fossil fuels. Given the rapidly depleting supplies of such fuels, an alternative source of phenol is eagerly sought.

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At first glance, “phenol production in bacteria” appears to be a paradoxical term, given the toxicity of phenol to microorganisms. A challenge, however, is what drives human endeavor and achievement, as exemplified by the latest research from Prof. Sang Yup Lee’s group at the Korea Advanced Institute of Science and Technology. In their paper published in Biotechnology Journal, Prof. Lee’s group use synthetic regulatory RNA technology to specifically knockdown genes in Escherichia coli, which in turn led to the increased production of tyrosine, the immediate precursor of phenol. Then, they introduced an enzyme to further convert tyrosine to phenol. The engineered strain had a final phenol titer and productivity of 3.79 g/L and 0.18 g/L/h, respectively, which is the highest titer achieved by microbial fermentation to date. Read the article online to see how Prof. Lee’s group were able to “coax” E. coli into producing phenol.

Source: Kim, B. et al. Metabolic engineering of Escherichia coli for the production of phenol from glucose. Biotechnol. J. 2013.

Related: Biotechnology Journal‘s special issue on “Metabolic Modeling and Simulation“, edited by Prof. Diethard Mattanovich and Prof. Vassily Hatzimanikatis

Novel approach in making top quality Italian sweet wines

Passito wine, generic name for Italian sweet wine, is made from dried grapes using ancient, traditional, and artisan winemaking techniques differing between regions. In North-East Italy winemakers use mouldy grapes to produce their very sweet wines. During the drying process and the wine grapes are infected by the grey fungus, Botrytis cinerea, which is under favourable conditions known in the wine industry as the ‘Noble Rot’. As a consequence of the mould infection, the juice in these grapes becomes increasingly sweet as they dehydrate. The juice from the raisinated grapes is subsequently fermented by yeast (e.g. Saccharomyces cerevisiae) in cellars during winter.

Unfortunately, the mould used for grape drying and the yeasts required for fermentation in passito wine making are still difficult to control by the winemakers. In traditional passito wine production which starts in Autumn without artificial environmental conditioning, the incidence of noble rot on slowly dehydrating grapes, is extremely variable and heavily dependant on weather conditions. The subsequent alcoholic fermentation is also a very delicate production step, because yeast activity is seriously hindered by the high sugar concentrations of the extra sweet grape juice as well as the low cellar temperatures in winter. A group of Italian microbiologists from the University of Verona therefore developed a novel protocol for the selection and characterization of indigenous moulds and yeasts to use as possible starter cultures in the production of passito style wines. The procedure consisted of several phases. First, the isolation of both moulds and yeasts from naturally withered grapes. The found Botrytis cinera and Saccharomyces cerevisiae strains were identified and typed, their performance evaluated with physiological and technological tests. Last but not least, the effect the selected fungi cultures have on the aroma profile of the wines was carefully examined. This protocol can help to improve the taste and quality reproducibility of the sweet Italian passito wines .As such, Azzonlini et al. provide a tool that enable winemakers to meet the delicate requirements of special wines by introducing modern technology and thus enhance the wines quality. /by FB Frédérique Belliard

Azzonlini et al. (2013), Selection of Botrytis cinerea and Saccharomyces cerevisiae strains for the improvement and valorization of Italian passito style wines. FEMS Yeast Research 13, 540-552

Posted in Biotechnology, Food, Microbiology | Tagged BiotecVisions, Botrytis cinerea, FEMS Yeast Research, fermentation, noble rot, S. cerevisae | Leave a reply

The complex microbiota of raw milk

Milk, due to its high nutritional content, can support a rich microbiota. These microorganisms enter milk from a variety of sources and, once in milk, can play a number of roles, both  promoting health and causing spoilage and disease  and not least,  facilitating dairy fermentations . 

The specific composition of the milk microbiota directly impacts on the subsequent development of dairy products .  Microorganisms can bring about the fermentation of milk through the production of lactate and have a variety of different impacts on the sensory, texture, flavour and organoleptic properties of resultant products

It is generally accepted that the lactic acid bacteria (LAB), a group of bacteria that ferment lactose to lactate, are a dominant population in bovine, goat, sheep and buffalo milk, prior to pasteurisation. The most common LAB genera in milk include Lactococcus, Lactobacillus, Leuconostoc, Streptococcus and Enterococcus. Other strains of non-LAB genera are also encountered in milk, as well as various yeasts and moulds . Human milk on the other hand is typically dominated by Streptococcus, Staphylococcus, Lactobacillus and Bifidobacterium spp. .

Quigley et al. have comprehensively reviewed   the various microbial populations found in raw milk and the methods employed for their detection. They also focus on   their sources, their subsequent significance with respect to industrial applications and the contribution of specific populations to food quality and health. They note that, in the food industry  the negative impact of removing LAB and other bacteria on subsequent food fermentations has been addressed for some time through their re-introduction in the form of starter and adjunct cultures. Similarly, once established definitively, it may be possible to restore the benefits associated with the consumption of raw milk and specific microorganisms therein, through the re-introduction of these microorganisms after processing. Thus, the microbial composition of raw milk is likely to continue to be the focus of much attention in the future. / by Gillian van Beest

Quigley et al.  (2013), The complex microbiota of raw milk. FEMS Microbiology Reviews, 37: 664–698.