Poly-γ-glutamic acid (γ-PGA) is a promising biopolymer for various applications.
In this study, we isolated a novel γ-PGA-producing strain, Bacillus halotolerans F29. The one-factor-at-a-time method was used to investigate the influence of carbon sources, nitrogen sources, and culture parameters on γ-PGA production. The optimal carbon and nitrogen sources were sucrose and (NH4)2SO4, respectively. The optimal culture conditions for γ-PGA production were determined to be 37 °C and a pH of 5.5. Response surface methodology was used to determine the optimum medium components: 77.6 g/L sucrose, 43.0 g/L monosodium glutamate, and 2.2 g/L K2HPO4. The γ-PGA titer increased significantly from 8.5 ± 0.3 g/L to 20.7 ± 0.7 g/L when strain F29 was cultivated in the optimized medium. Furthermore, the γ-PGA titer reached 50.9 ± 1.5 g/L with a productivity of 1.33 g/L/h and a yield of 2.23 g of γ-PGA/g of L-glutamic acid with the optimized medium in fed-batch fermentation. The maximum γ-PGA titer reached 45.3 ± 1.1 g/L, with a productivity of 1.06 g/L/h when molasses was used as a carbon source. It should be noted that the γ-PGA yield in this study was the highest of all reported studies, indicating great potential for the industrial production of γ-PGA.
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Strain KSNA2T, a Gram-negative, moderately halophilic, facultatively
anaerobic, motile, rod-shaped bacterium, was isolated
from the surface-sterilized stem tissue of a beach morning
glory (Calystegia soldanella) plant in Chuja Island, Jejudo,
Republic of Korea. Phylogenetic analysis based on 16S
rRNA gene and whole-genome sequences revealed that strain
KSNA2T formed a distinct lineage within the family Enterobacteriaceae,
with the highest 16S rRNA gene sequence similarity
to Izhakiella australiensis KCTC 72143T (96.2%) and
Izhakiella capsodis KCTC 72142T (96.0%), exhibited 95.5–
95.9% similarity to other genera in the family Enterobacteriaceae
and Erwiniaceae. Conserved signature indels analysis
elucidated that strain KSNA2T was delimited into family
Enterobacteriaceae. KSNA2T genome comprises a circular
chromosome of 5,182,800 bp with 56.1% G + C content. Digital
DNA-DNA relatedness levels between strain KSNA2T
and 18 closely related species were 19.3 to 21.1%. Average
nucleotide identity values were between 72.0 and 76.7%.
Growth of strain KSNA2T was observed at 4 to 45°C (optimum,
25°C) and pH 5.0 to 12.0 (optimum, pH 7.0) in the
presence of 0 to 11% (w/v) NaCl (optimum, 0–7%). The major
cellular fatty acids (> 10%) were C16:0 followed by summed
feature 8 (C18:1 ω7c and/or C18:1 ω6c), summed feature
3 (C16:1 ω7c and/or C16:1 ω6c), C17:0 cyclo, and C14:0. The major
isoprenoid quinone was ubiquinone-8 (Q-8). With combined
phylogenetic, genomic, phenotypic, and chemotaxonomic
features, strain KSNA2T represents a novel species of
a new genus in the family Enterobacteriaceae, for which the
name Jejubacter calystegiae gen. nov., sp. nov. is proposed.
The type strain is KSNA2T (= KCTC 72234T = CCTCC AB
2019098T).
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