Biology subjects

Temovska, M.

Publications and source records attributed to Temovska, M..

3 recordsLinked to original sources

bioRxiv2024

Lactate production from lactose-rich wastewater: A comparative study on reactor configurations to maximize conversion rates and efficiencies

About 90% of global lactate production is derived from bacterial fermentation of sugars via pure cultures of homofermentative bacteria in batch mode. Acid whey, which is a wastewater from the yogurt industry with lactose and galactose as the main sugars, can be used as an alternative substrate for the commercial production of lactate. Operating open cultures of microbial consortia (i.e., reactor microbiomes) reduces the costs of lactate production by circumventing sterilization, while continuous operation achieves higher productivity at shorter production times. Homofermentation can be achieved by maintaining acidic and thermophilic conditions, while product formation in continuous systems can be increased with biomass retention strategies. To find the best reactor configuration for lactate production from acid whey, we operated three different reactor configurations: (1) an upflow anaerobic sludge blanket (UASB) reactor; (2) an anaerobic filter reactor (AFR); and (3) an anaerobic continuously stirred tank reactor (CSTR) with a hollow-fiber membrane module. We operated at different hydraulic retention times (HRTs) to find the optimum parameters to maximize the lactose and galactose-into-lactate (LG-into-LA) conversion efficiency. We did not use an inoculum but enriched the endogenous D-lactate-producing Lactobacillus spp. that later dominated the reactor microbiomes (> 90% relative abundance). Undissociated lactic acid concentrations of more than 60 mmol C L-1 inhibited the microbiomes. We alleviated the inhibition effect by shortening the HRT to 0.6 days and using diluted acid-whey substrate (1.67-fold dilution) to achieve almost complete conversion of the acid-whey sugars to lactate. At the 0.6-day HRT commencement, the AFR and CSTR performed better than the UASB reactor due to their better cell retention abilities. During the period between Day 365-384, we experienced an error in the pH control of the CSTR system during which the pH value dropped to 4.3. After this pH-error period, the LG-into-LA conversion efficiency for the CSTR considerably improved and surpassed the AFR. We achieved the highest lactate conversion rate of 1256 {+/-} 46.3 mmol C L-1 d-1 (1.57 {+/-} 0.06 g L-1 h-1) at a LG-into-LA conversion efficiency of 82.2 {+/-} 3.4% (in mmol C), with a yield of 0.85 {+/-} 0.02 mmol C mmol C-1 (product per consumed substrate) for the CSTR.

bioengineering↗

bioRxiv2023

Exclusive D-lactate-isomer production during a reactor-microbiome conversion of lactose-rich waste by controlling pH and temperature

Lactate is among the top-ten-biobased products. It occurs naturally as D- or L-isomer and as a racemic mixture (DL-lactate). Generally, lactate with a high optical purity is more valuable. In searching for suitable renewable feedstocks for lactate production, unutilized organic waste streams are increasingly coming into focus. Here, we investigated acid whey, which is a lactose-rich byproduct of yogurt production, that represents a considerable environmental footprint for the dairy industry. We investigated the steering of the lactate-isomer composition in a continuous and open culture system (HRT = 0.6 d) at different pH values (pH 5.0 vs. pH 6.5) and process temperatures (38{degrees}C to 50{degrees}C). The process startup was achieved by autoinoculation. At a pH of 5.0 and a temperature of 47{degrees}C-50{degrees}C, exclusive D-lactate production occurred because of the dominance of Lactobacillus spp. (> 95% of relative abundance). The highest volumetric D-lactate production rate of 722 {+/-} 94.6 mmol C L-1 d-1 (0.90 {+/-} 0.12 g L-1 h-1), yielding 0.93 {+/-} 0.15 mmol C mmol C-1, was achieved at a pH of 5.0 and a temperature of 44{degrees}C (n = 18). At a pH of 6.5 and a temperature of 44{degrees}C, we found a mixture of DL-lactate (average D-to-L-lactate production rate ratio of 1.69 {+/-} 0.90), which correlated with a high abundance of Streptococcus spp. and Enterococcus spp. However, exclusive L-lactate production could not be achieved. Our results show that for the continuous conversion of lactose-rich dairy waste streams, the pH was a critical process parameter to control the yield of lactate isomers by influencing the composition of the microbiota. In contrast, temperature adjustments allowed the improvement of bioprocess kinetics.

bioengineering↗

bioRxiv2020

The isolate Caproiciproducens sp. 7D4C2 produces n-caproate at mildly acidic conditions from hexoses: genome and rBOX comparison with related strains and chain-elongating bacteria

BackgroundBulk production of medium-chain carboxylates (MCCs) with 6-12 carbon atoms is of great interest to biotechnology. Open cultures (e.g., reactor microbiomes) have been utilized to generate MCCs in bioreactors. When in-line MCC extraction and prevention of product inhibition is required, the bioreactors have been operated at mildly acidic pH (5.0-5.5). However, model chain-elongating bacteria grow optimally at neutral pH values. Here, we isolated a chain-elongating bacterium (strain 7D4C2) that thrives at mildly acidic pH. We studied its metabolism and compared its whole genome and the reverse {beta}-oxidation (rBOX) genes to other bacteria. ResultsStrain 7D4C2 produces lactate, acetate, n-butyrate, n-caproate, biomass, and H2/CO2 from hexoses. With only fructose as substrate (pH 5.5), the maximum n-caproate specificity (i.e., products per other carboxylates produced) was 60.9 {+/-} 1.5%. However, this was considerably higher at 83.1 {+/-} 0.44% when both fructose and n-butyrate (electron acceptor) were combined as a substrate. A comparison of serum bottles with fructose and n-butyrate with an increasing pH value from 4.5 to 9.0 showed a decreasing n-caproate specificity from [~]92% at mildly acidic pH (pH 4.5-5.0) to [~]24% at alkaline pH (pH 9.0). Moreover, when carboxylates were extracted from the broth (undissociated n-caproic acid was [~]0.3 mM), the n-caproate selectivity (i.e., product per substrate fed) was 42.6 {+/-} 19.0% higher compared to serum bottles without extraction. Based on the 16S rRNA gene sequence, strain 7D4C2 is most closely related to the isolates Caproicibacter fermentans (99.5%) and Caproiciproducens galactitolivorans (94.7%), which are chain-elongating bacteria that are also capable of lactate production. Whole-genome analyses indicate that strain 7D4C2, C. fermentans, and C. galactitolivorans belong to the same genus of Caproiciproducens. Their rBOX genes are conserved and located next to each other, forming a gene cluster, which is different than for other chain-elongating bacteria such as Megasphaera spp. ConclusionsCaproiciproducens spp., comprising strain 7D4C2, C. fermentans, C. galactitolivorans, and several unclassified strains, are chain-elongating bacteria that encode a highly conserved rBOX gene cluster. Caproiciproducens sp. 7D4C2 (DSM 110548) was studied here to understand n-caproate production better at mildly acidic pH within microbiomes and has the additional potential as a pure-culture production strain to convert sugars into n-caproate.

microbiology↗