Complete genome sequencing of newly isolated thermotolerant Corynebacterium glutamicum N24 provides a new insights into its thermotolerant phenotype

Potassium ion leakage impairs thermotolerance in Corynebacterium glutamicum

Corynebacterium glutamicum, a gram-positive bacterium, can produce amino acids such as glutamic acid and lysine. The heat generated during cell growth and/or glutamate fermentation disturbs both the cell growth and fermentation. To overcome such a negative effect of the fermentation heat, we have tried to establish a high temperature fermentation. One of the approach is to create a thermotolerant strains, while the other is to create an optimum culture conditions able for the strain to grow at higher temperatures. In this study, we focused on the latter approach, where we examined the effect of potassium ion on cell growth at high growth temperatures of C. glutamicum. The supplementation of high concentrations of potassium chloride (300 mM) (or sorbitol, an osmolyte) mitigated the repressed cell growth induced by high temperature at 39 °C or 40 °C. The intracellular potassium concentration declines from 300 mM to ∼150 mM by increasing the growth temperature but not by supplementing potassium chloride or sorbitol. Furthermore, in vitro experiments revealed that the potassium ion leakage occurs at high temperatures, which was mitigated in the presence of high concentrations of extracellular potassium chloride. This suggested that the presence of high osmolyte in the culture medium could inhibit the potassium ion leakage induced by high temperature and subsequently support cell growth at high temperatures.

Corynebacterium suranareeae sp. nov., a glutamate producing bacterium isolated from soil and its complete genome-based analysis

Strain N24T was isolated from soil contaminated with starling’s feces collected from Roi-Et province, Thailand. Cells of N24T were Gram-stain-positive rods, aerobic and non-spore-forming. N24T was positive for catalase, urease, citrate utilization, nitrate reduction and Methyl Red (MR) test but negative for oxidase, casein, gelatin liquefaction, tyrosine, Voges–Proskauer (VP) reaction and starch hydrolysis. Meso-diaminopimelic acid, rhamnose, ribose, arabinose and galactose were detected in its whole-cell hydrolysates. The results of the 16S rRNA gene sequence analysis indicated that N24T represented a member of the genus Corynebacterium . N24T was closely related to Corynebacterium glutamicum ATCC 13032T, with 99.0 % 16S rRNA gene sequence similarity. According to results obtained using in silico DNA–DNA hybridization approaches, N24T showed highest DNA–DNA relatedness (27.6 %) and average nucleotide identity (84.1 %) to Corynebacterium glutamicum ATCC 13032T. The DNA G+C content of N24T was 51.8 mol% (genome based). The major cellular fatty acids of N24T were C16 : 0, and C18 : 1ω9c. N24T had the nine isoprenes unit, MK-9(H2) as the predominant menaquinone. The predominant polar lipids were phosphatidylglycerol, phosphatidylinositol and diphosphatidylglycerol. Mycolic acids were also present. According to the complete genome sequence data, strain N24T and C. glutamicum ATCC 13032T are close phylogenetic neighbours, but have different genome characteristics. On the basis of the results of the genotypic and genomic studies and phenotypic characteristics including chemotaxonomy, strain N24T should be classified as representing a novel species of the genus Corynebacterium , for which the name Corynebacterium suranareeae sp. nov. is proposed. The type strain is N24T (TBRC 5845T=NBRC 113465T).

Two-stage air stripping combined with hydrolysis acidification process for coal gasification wastewater pretreatment

Coal gasification wastewater is mainly from gas washing, condensation and purification processes in the gas furnace with high NH₃-N (nitrogen in water in the form of free ammonia (NH₃) and ammonium ion (NH₄ ⁺)), TN (total nitrogen) and refractory organics content, which will inhibit the subsequent biological treatment. The 'air stripping - hydrolysis acidification - air stripping' process was proposed as the pretreatment for coal gasification wastewater to improve the biodegradability and nitrogen removal, which could reduce the subsequent biological treatment load. The first-stage air stripping process before hydrolysis acidification could achieve a significant removal of NH₃-N (97.0%) and volatile phenol (70.0%), reducing the corresponding toxicity on hydrolysis acidification. The group with air stripping had more abundant microbial communities and a more effective organic degradation performance in hydrolysis acidification than that without air stripping. The second-stage air stripping removed NH₃-N released from hydrolysis acidification, and significantly reduced the TN concentration in effluent. The whole process achieved a TN removal from 2,000 ± 100 mg/L to 160 ± 80 mg/L, and a total phenols removal from 700 ± 50 mg/L to 80 ±20 mg/L.