while Bacilli is the class to which the order Lactobacillales belongs to.

Transcription

1 Interactive Questions Question 1: Lactic acid bacteria belong to which order? Lactobacillaceae Lactobacillales Lactobacillales is the correct order. Lactobacillaceae is one family within this order, while Bacilli is the class to which the order Lactobacillales belongs to. Bacilli Question 2: The energy efficiency of the carbon metabolism of lactic acid bacteria is...?...high...high or low depending if oxygen is present...low The energy efficiency of the carbon metabolism of lactic acid bacteria is generally low as it strictly depends on substrate level phosphorylation. Under standard conditions they are not able to gain ATP by respiration. Even if oxygen is present as electron acceptor, its reduction to water yields no ATP. This means that usually not more than 1 or 2 ATP are gained by catabolizing one molecule of sugar. Question 3: What are the building blocks of bacterial microcompartments? - 1 -

2 Only proteins BMCs are nanoreactor-like structures, whose shells are constituted of proteins only. Kerfeld C.A. and Erbilgin O. (2015) Bacterial microcompartments and the modular construction of microbial metabolism. Trends Microbiol. 23, Only polysaccharides Proteins and polysaccharides Proteins and DNA Question 4: Which size has the smallest genome of a Lactobacillus strain found so far? 2.45 Mb 0.98 Mb 1.23 Mb A recent study focusing on Lactobacilli found the smallest genome in Lactobacillus sanfranciscensis (1.23 Mb) and the largest in Lactobacillus parakefiri (4.91 Mb). Sun Z. et al. (2015) Expanding the biotechnology potential of lactobacilli through comparative genomics of 213 strains and associated genera. Nat. Commun. 6,

3 5.43 Mb Question 5: Which are the fermentation products of heterofermentative lactic acid bacteria from glucose? Only lactic acid Lactic acid and ethanol Lactic acid and acetic acid Lactic acid and carbon dioxide Lactic acid, acetic acid and/or ethanol and carbon dioxide This answer is correct. Glucose is converted to xylulose-5-phosphate, whereby one molecule of carbon dioxide is liberated. The following key-enzyme is the phosphoketolase, splitting xylulose-5-phosphate into pyruvate and acetyl-phosphate. Pyruvate is reduced to lactate. Acetyl-phosphate is converted to acetate or ethanol, depending on the presence or absence of further electron acceptors. Gänzle M.G. (2015) Lactic metabolism revisited: metabolism of lactic acid bacteria in food fermentations and food spoilage. Current Opinion in Food Science 2, Question 6: The homofermentative sugar catabolism of lactic acid bacteria proceeds via which pathway? Embden-Meyerhof-Parnas pathway - 3 -

4 This is correct. The heterofermentative catabolism proceeds via the phosphoketolase pathway. The Entner-Doudoroff pathway proceeds via the key-enzyme 2-keto-3-deoxyphosphogluconate aldolase, which is absent in lactic acid bacteria. Gänzle M.G. (2015) Lactic metabolism revisited: metabolism of lactic acid bacteria in food fermentations and food spoilage. Current Opinion in Food Science 2, Phosphoketolase pathway Entner-Doudoroff pathway Question 7: Which trait is beneficial for lactic acid bacteria for use in industrial microbiology? High sugar uptake rate High productivities are a prerequisite for economic microbial chemical production processes. The first step in a fermentation is the sugar uptake. The sugar uptake rate limits all subsequent steps, therefore microorganisms with a high sugar uptake rate are sought after. Lactic acid bacteria show a very high sugar uptake rate, comparable to that of other biotech workhorses, such as Escherichia coli or Saccharomyces cerevisiae. A genetic toolbox would be also very desirable, but unfortunately many lactic acid bacteria are recalcitrant to transformation up to now, hindering their development as cell factories. This is one of the main tasks to develop in the near future. Low sugar uptake rate Many genetic tools available for all species and strains Question 8: Which trait is detrimental for industrial exploitation of lactic acid bacteria? - 4 -

5 High temperature tolerance Auxotrophies - they are fastidious organisms Their strict demand for organic nitrogen sources and many vitamins leads to increased growth media costs and to problems for the purification of the fermentation products. This is definitely a disadvantage for the use of lactic acid bacteria for chemical production and a problem to be addressed in the near future. Many of them can withstand high temperatures - this is an advantage, as cooling is generally expensive. The limited number of fermentation products is not necessarily a disadvantage as many of them are industrially relevant and metabolic engineering opens the door to other products - provided the genetic toolbox is being developed. Limited number of fermentation products - 5 -