Production of lactobionic acid at high salt concentrations by Acinetobacter halotolerans isolated from seaside soil

A lactobionic acid (LBA)-producing bacterium isolated from seaside soils was identified as Acinetobacter halotolerans and designated as strain KRICT-1. We determined whether KRICT-1 can produce LBA at high salt concentrations. The KRICT-1 strain grew on a nutrient broth (NB) agar plate with up to 7.0% NaCl, indicating high NaCl tolerance, and 30 degrees C was the optimum growth temperature for LBA production. We produced LBA using the KRICT-1 strain in NB medium containing various concentrations of NaCl. While Pseudomonas taetrolens, an efficient LBA-producing bacterium, could produce LBA with up to 5.5% NaCl, the KRICT-1 strain could produce LBA at up to 7.0% NaCl and produced more LBA than P. taetrolens with over 5.5% NaCl. We produced LBA using NB medium containing 7.0% NaCl by batch fermentation of the KRICT-1 strain in a 5 L fermenter. The LBA production titer and productivity of the KRICT-1 strain were 32.1 g/L and 0.22 g/L/h, respectively, which were approximately 1.35- and 1.38-fold higher than those (23.7 g/L and 0.16 g/L/h) obtained from flask culture. Additionally, quinoprotein glucose dehydrogenase is an LBA-producing enzyme in A. halotolerans. We demonstrated that the A. halotolerans KRICT-1 strain is appropriate for LBA production at high salt concentrations

Isolation and Characterization of a New Superior Lactobionic Acid-Producing Bacterium, <i>Enterobacter cloacae</i> KRICT-1, from Environmental Soil Samples

Lactobionic acid (LBA) is a specialty aldonic acid that has been broadly employed in various industries, including food, cosmetics, and pharmaceuticals. In this study, we isolated a new excellent LBA-producing bacterium from soil, designated as strain KRICT-1. A phylogenetic analysis revealed that this strain was identified as Enterobacter cloacae. Previously, we successfully produced LBA using Pseudomonas taetrolens, an excellent LBA-producing bacterium. In a flask culture at 30 ??C, E. cloacae KRICT-1 showed the same LBA production concentration (209.3 g/L) and yield (100%) from 200 g/L lactose, compared with those obtained from P. taetrolens cultivated at 25 ??C, the growth temperature of which showed the highest LBA production ability. E. cloacae KRICT-1 exhibited an approximately 1.08-fold higher LBA productivity (8.37 g/L/h) than that (7.75 g/L/h) of P. taetrolens, indicating that E. cloacae KRICT-1 was a more efficient LBA-producing bacterium than P. taetrolens. The LBA productivity of E. cloacae KRICT-1 further improved to 8.72 g/L/h at 35 ??C. Furthermore, the LBA productivity (9.97 g/L/h) improved at 35 ??C in a 5 L fermenter. After whole-genome sequencing of E. cloacae KRICT-1, we found that two quinoprotein glucose dehydrogenases (GDH1 and GDH2) from this strain could produce LBA from lactose by recombinantly expressing these genes in Escherichia coli. Our present results clearly demonstrated that E. cloacae KRICT-1 can be a new promising host for the industrial production of LBA

Value-added conversion of biodiesel into the versatile biosurfactant sophorolipid using Starmerella bombicola

In this study, we tested whether biodiesel could be used as a feedstock for the microbial synthesis of sophorolipid, a high value-added chemical. Sophorolipid was successfully produced from Starmerrella bombicola using biodiesel as a hydrophobic substrate. Fed-batch fermentation was carried out for the high-level production. Compared to flask culture, the sophorolipid production concentration significantly increased from 58.1 ​g/L to 224.2 ​g/L (an approximate increase of 386%) using fed-batch fermentation, which is the highest value ever reported using fatty acid methyl esters and fatty acid ethyl esters as hydrophobic substrates. Different from rapeseed oil-based sophorolipid (ROSL), the biodiesel-based sophorolipid (BDSL) contained a new type of sophorolipid called esterified sophorolipid (approximately 19.8%). The BDSL demonstrated better surface-active properties, lower surface tension (34.2 vs. 35.8 ​mN/m, respectively), and a decreased critical micelle concentration (25.1 vs. 26.3 ​mg/L, respectively) compared to the ROSL. Given these results, the BDSL is expected to be used in various industrial fields where vegetable oil-based sophorolipids, the commercialized forms of sophorolipids, have been used. To our knowledge, this is the first report to describe the conversion of biodiesel for the production of a high value-added chemical

High-Level Production of Bacteriotoxic Phospholipase A1 in Bacterial Host Pseudomonas fluorescens via ABC Transporter-Mediated Secretion and Inducible Expression

Bacterial phospholipase A1 (PLA1) is used in various industrial fields because it can catalyze the hydrolysis, esterification, and transesterification of phospholipids to their functional derivatives. It also has a role in the degumming process of crude plant oils. However, bacterial expression of the foreign PLA1-encoding gene was generally hampered because intracellularly expressed PLA1 is inherently toxic and damages the phospholipid membrane. In this study, we report that secretion-based production of recombinant PlaA, a bacterial PLA1 gene, or co-expression of PlaS, an accessory gene, minimizes this harmful effect. We were able to achieve high-level PlaA production via secretion-based protein production. Here, TliD/TliE/TliF, an ABC transporter complex of Pseudomonas fluorescens SIK-W1, was used to secrete recombinant proteins to the extracellular medium. In order to control the protein expression with induction, a new strain of P. fluorescens, which had the lac operon repressor gene lacI, was constructed and named ZYAI strain. The bacteriotoxic PlaA protein was successfully produced in a bacterial host, with help from ABC transporter-mediated secretion, induction-controlled protein expression, and fermentation. The final protein product is capable of degumming oil efficiently, signifying its application potential