Production of L-lactic acid by acid-resistant strain enterococcus faecalis under controlled conditions
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GOLOVNYOVA, Natalya; SCHATKO, Vitaly; SAMARTSEV, Andrey; BUKO, Andrey. Production of L-lactic acid by acid-resistant strain enterococcus faecalis under controlled conditions. In: Microbial Biotechnology. Ediția 3, 12-13 octombrie 2016, Chișinău. Chișinău, Republica Moldova: Institutul de Microbiologie şi Biotehnologie, 2016, p. 181.
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Microbial Biotechnology
Ediția 3, 2016
Conferința "Microbial Biotechnology"
Chișinău, Moldova, 12-13 octombrie 2016

Production of L-lactic acid by acid-resistant strain enterococcus faecalis under controlled conditions


Pag. 181-181

Golovnyova Natalya, Schatko Vitaly, Samartsev Andrey, Buko Andrey
 
Institute of Microbiology of the NAS of Belarus
 
Disponibil în IBN: 15 martie 2019



Teza

Nowadays numerous studies are focused on microbial synthesis from renewable vegetal materials of optically pure lactic acid to be further used as monomeric substrate for manufacturing unique bio- and photodegradable polymeric compounds – poly-L-hydroxypropionates (polylactates) (1). Lactic acid isomers produced by bacterial or fungal fermentation of various carbohydrate-rich substances (starch, molasses, milk whey) are engaged in polymerization technologies (2). In some cases semi-continuous fed-batch culture enables to raise considerably the efficiency of microbial synthesis as compared to conventional batch process. The aim of this study was to investigate features of producing optically pure L-lactic acid by pre-selected acid-resistant strain Enterococcus faecalis in fed-batch culture. Submerged culture of bacteria Enterococcus faecalis was conducted in the fermenter of 3 L volume in the nutrient medium comprising utilized substrate (glucose, sucrose or molasses) in concentration range 10 to 200 d/L, yeast extract – 0.5 to 2 %, mineral salts. In the course of anaerobic fermentation sterile concentrated substrate solution was continuously fed and the parameters of titratable acidity, biomass accumulation, concentrations of lactic acid and carbohydrates were controlled. To neutralize metabolic products 20 % NH4OH was added into the medium and pH was maintained minimum at 6.8 value. Bacterial biomass was evaluated nephelometrically at 590 nm. Total carbohydrate level was estimated by anthrone method, the amount of synthesized L-lactate was determined enzymatically using commercial bioMerieux or Bio Vision test kits. The maximum specific growth rate of the bacterial culture (μ = 0.3 h-1) was achieved in the case of 3 h submerged fed-batch fermentation and did not exceed 0.1 h-1 thereafter. When the process was carried out in 6-cycle mode it was found that productivity of the culture reached its maximum by the third run and declined 2-fold in the final round (by 9–10 days). Accumulation of biomass and lactic acid in the cultural liquid tended to grow in the third cultural cycle and was accompanied by intense assimilation of carbohydrates. Every 2 days of fed-batch fermentation witnessed increased productivity of the process – starting from 3.6 g/l/h during initial 48 h up to 7.3 g/l/h in the third cycle. The obtained data will be helpful in optimizing technology of lactic acid biosynthesis.