Kingkaew, Engkarat

Preferred name

Kingkaew, Engkarat

Main Affiliation

School of Science

engkarat.ki@kmitl.ac.th

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Antioxidant Activity, γ-Aminobutyric Acid, and Genome Analysis of Lactiplantibacillus plantarum FL13-2 from Fermented Rice Flour
(2025-09-01)
Songsumanus, Apakorn
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Pinyosnit, Natawadee
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Kingkaew, Engkarat
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Panngeun, Thanapol
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Charunanthasunthon, Worasan
Ten rod-shaped isolates of lactic acid bacteria (LAB) from the traditional fermented rice flour, khao-khab were identified as belonging to the genus Lactobacillus based on phenotypic characteristics. Group I isolates (FL12-1, FL18-1, FL19-1S, FL23-1, FL24-1, FL25-1, and FL26-1) were closely related to Limosilactobacillus fermentum, exhibiting 16S rRNA gene sequence similarity of 99.4%–100%. Group II included FL13-2 and FL22-2 (Group IIA) and FL17B (Group IIB), closely related to Lactiplantibacillus plantarum (99.9%–100%) and Lactiplantibacillus pentosus (100%), respectively. All isolates demonstrated strong antioxidant potential, with 2,2-Diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity—measured by the standard DPPH assay—ranging from 78.49±1.01% to 91.18±3.95%, surpassing that of ascorbic acid. Strain FL13-2, identified as L. plantarum through genomic analysis (Average Nucleotide Identity (ANI) 98.5%, digital DNA-DNA hybridization (dDDH) 92.5%), produced 2.43 g/L of γ-aminobutyric acid (GABA). It harbored key biosynthesis and transport genes (gadB, gadC, gatABCD, pdxK). Phylogenetic analysis confirmed high sequence similarity of these genes with other LAB strains, supporting their functional roles. The gad system was implicated in acid resistance and GABA production under low pH conditions. Genome annotation revealed bacteriocin genes (Enterocin X β, Plantaricin E, and F) and indicated low pathogenicity and absence of virulence factors. Antimicrobial resistance genes (vanH, vanT, vanY) were detected; however, these are intrinsic to LAB and associated with essential cell wall biosynthesis rather than acquired resistance. Additionally, the presence of the qacJ efflux pump and hlyIII gene—both commonly found in probiotic strains—further supports the safety profile of FL13-2. These findingshighlight L. plantarum FL13-2 as a promising multifunctional probiotic candidate with potent antioxidative, GABA-producing, and antimicrobial properties.
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Genomic insights into arsenic and antibiotic resistance in Comamonas thiooxydans strains F1-6 and A7-5
(2026-04-01)
Sitlaothaworn, Kanchana
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Phongsopitanun, Wongsakorn
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Chitpirom, Kitja
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Kingkaew, Engkarat
;
Lee, Jung Sook
Two arsenic-resistant, Gram-negative, aerobic rod-shaped bacterial strains, F1-6 and A7-5, which were isolated from agricultural soil in Thailand, were systematically studied. They grew at 30 °C, pH 5–11, and in 3% (w/v) NaCl. Ubiquinone with eight isoprene units (Q-8) and the cellular fatty acids C1<inf>6:0</inf>, C<inf>18:1</inf> ω7c, and C<inf>17:0</inf> CYCLO were the major components. Phylogenetic analysis via 16S rRNA gene sequences revealed that strains F1-6 and A7-5 were affiliated with the genus Comamonas and closely related to C. thiooxydans DF2T and C. testosteroni KCTC 2990T, with 99.79% and 99.86% similarity, respectively. The average nucleotide identity and digital DNA-DNA hybridization values between F1-6 and C. thiooxydans DF2T were 97.89% and 85.7%, respectively, whereas those between A7-5 and C. thiooxydans DF2T were 97.23% and 81.3%, respectively. Thus, both the F1-6 and A7-5 were identified as C. thiooxydans. The draft genome sizes of F1-6 and A7-5 were 5.2 and 5.3 Mb, comprising 87 and 84 contigs, with DNA G+C contents of 61.5% and 61.4%, respectively. The genomes of both strains contained ars cluster genes and many genes for growth and resistance to heavy metals and antibiotics, similar to those of C. testosteroni ATCC 11996T, C. thiooxydans CNB-1 substr. CNB-2 Chr, and C. terrae NBRC 106524T. Nevertheless, the acr3, qacG, and vanH genes in the vanO cluster were found only in C. terrae NBRC 106524T. This study provides more comprehensive insight into As-resistant bacteria and could be applied to the bioremediation of As and other heavy metals in the future.
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Lentilactobacillus terminaliae sp. nov., isolated from tree bark (Terminalia ivorensis Chev.) and its antioxidant activity
(2025-01-01)
Phuengjayaem, Sukanya
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Kingkaew, Engkarat
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Chamroensaksri, Nitcha
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Phongsopitanun, Wongsakorn
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Tanasupawat, Somboon
A Gram-stain-positive, facultatively anaerobic, rod-shaped strain, designated SPB1-3T, was isolated from tree bark. This strain exhibited heterofermentative production of dl-lactic acid from glucose. Optimal growth was observed at 25–40 °C, pH 4.0–7.0, and in the presence of 3% (w/v) NaCl. The cell wall peptidoglycan contained lysine and aspartic acid. The predominant fatty acids identified were C<inf>16:0</inf> and the Summed feature 7 (C<inf>19:1</inf> ω7c/C<inf>19:1</inf> ω6c and/or C<inf>19:1</inf> ω6c/ω7c/19cy). The polar lipid profile included phosphatidylglycerol, diphosphatidylglycerol and phosphatidylinositol, along with two unidentified phospholipids, two unidentified amino lipids and two unidentified lipids. Phylogenetic analysis based on 16S rRNA gene sequences positioned strain SPB1-3T within the genus Lentilactobacillus, showing a close relation to Lentilactobacillus kosonis NBRC 111893T (99.86%) and Lentilactobacillus curieae CCTCC M 2011381T (98.65%). The whole genome of strain SPB1-3T comprised 1 932 998 base pairs with 1955 coding genes and a DNA G+C content of 37.8%. Digital DNA–DNA hybridization between strain SPB1-3T and closely related type strains ranged from 19.50 to 27.20%. The average nucleotide identity ranged from 84.21 to 85.56%, and the average amino acid identity ranged from 57.25 to 85.99%, both falling below the established thresholds for species delineation. Strain SPB1-3T was clearly distinguishable from related Lentilactobacillus species based on its phenotypic and chemotaxonomic char-acteristics, 16S rRNA gene sequence similarity and whole genome analysis. Additionally, the strain exhibited radical scavenging activity at 66.92% and demonstrated 82.32% inhibition in the tyrosinase inhibitory assay. These findings support the classification of strain SPB1-3T as a novel species within the genus Lentilactobacillus, for which the name Lentilactobacillus terminaliae sp. nov. is proposed. The type strain is SPB1-3T (=JCM 35081T=TISTR 10005T).
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Paracraurococcus lichenis sp. nov., isolated from lichen in Thailand
(2024-10-01)
Kingkaew, Engkarat
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Kato, Shingo
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Iino, Takao
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Itoh, Takashi
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Ohkuma, Moriya
A novel bacterium, designated as strain LOR1-02T and isolated from a lichen sample collected from Kham Riang Subdistrict, Kantharawichai District, Maha Sarakham Province, Thailand, underwent thorough investigation utilizing a polyphasic taxonomic approach. Strain LOR1-02T demonstrated growth within a temperature range of 20–42 °C (optimal at 30 °C), pH range of 5.0–7.5 (optimal at pH 7.0), and tolerance to 4.0% (w/v) NaCl. Phylogenetic analysis revealed its close relation to Paracraurococcus ruber JCM 9931T, with a 16S rRNA gene sequence similarity of 97.16%, placing it within the genus Paracraurococcus. The approximate genome size of strain LOR1-02T was determined to be 8.6 Mb, with a G + C content of 70.9 mol%. Additionally, ANIb, ANIm, and AAI values between the whole genomes of strain LOR1-02T and type strains were calculated as 82.6–83.4%, 86.1–86.8%, and 81.4–82.2%, respectively, while the dDDH value was determined to be 26.3–28.5% (C.I. 24.0–31.0%). The predominant fatty acids detected were C<inf>18:1</inf>ω7c and/or C<inf>18:1</inf>ω6c, C<inf>16:0</inf>, and C<inf>18:1</inf>2OH. The major ubiquinone identified was Q-10, and the polar lipids included phosphatidylglycerol, phosphatidylethanolamine, phosphatidylcholine, diphosphatidylglycerol, along with unidentified phosphoaminolipid, lipids, and an amino lipid. Based on comprehensive phenotypic, chemotaxonomic, and genotypic characterization, it is concluded that strain LOR1-02T represents a novel species within the genus Paracraurococcus, for which the name Paracraurococcus lichenis sp. nov. is proposed. The type strain designation is LOR1-02T (= JCM 33121T = NBRC 112776T = TISTR 2503T).
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Genomic Characterization and Hydrolysis Enzyme of Piscibacillus salipiscarius RBU1-1ᵀ and Allobacillus salarius SKP4-8ᵀ Isolated from Fermented Fish Products
(2026-01-01)
Namwong, Sirilak
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Chaimongkol, Apichai
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Kingkaew, Engkarat
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Phongsopitanun, Wongsakorn
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Chamroensaksri, Nitcha
Two halophilic bacterial strains, Piscibacillus salipiscarius RBU1-1ᵀ and Allobacillus salarius SKP4-8ᵀ, were isolated from traditional Thai fermented foods, namely pla-ra from Ratchaburi, Thailand, and ka-pi from Samut Sakhon, Thailand, respectively. Comparative genomics confirmed their taxonomic distinctiveness, with RBU1-1ᵀ representing a novel species and SKP4-8ᵀ showing clear genomic separation from its closest relatives. The draft genomes were 2.99 Mb (36.7 mol% G+C) for RBU1-1ᵀ and 2.59 Mb (38.8 mol% G+C) for SKP4-8ᵀ. Both strains encoded hydrolytic enzymes and secondary metabolite pathways, with SKP4-8ᵀ displaying higher protease activity and RBU1-1ᵀ harboring ectoine biosynthetic and stress-response genes. RBU1-1ᵀ encoded the biosynthesis pathways for ectoine, tryptophan, and thiamine, while SKP4-8ᵀ encoded thiamine, riboflavin, coenzyme A, and menaquinone, indicating their potential contributions to postbiotic and nutritional value. Safety assessment revealed the absence of biogenic amine, antibiotic biosynthesis, and major virulence genes in both strains. Although antimicrobial resistance-associated genes were detected, no complete clusters were identified, suggesting low phenotypic risk. Computational pathogenicity prediction indicated a low probability for RBU1-1ᵀ (0.242) and a higher probability for SKP4-8ᵀ (0.945), though these require cautious interpretation. Overall, genomic evidence and enzymatic activity support RBU1-1ᵀ and SKP4-8ᵀ as safe, functional starter culture candidates, with RBU1-1ᵀ showing strong potential through postbiotic biosynthesis and SKP4-8ᵀ through proteolytic activity.

Kingkaew, Engkarat

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