Journal of Microbiology

Volume 60(9); September 2022

Journal Articles

[PROTOCOL]Analyzing viral epitranscriptomes using nanopore direct RNA sequencing: Ari Hong , Dongwan Kim , V. Narry Kim , Hyeshik Chang; J. Microbiol. 2022;60(9):867-876. Published online August 24, 2022; DOI: https://doi.org/10.1007/s12275-022-2324-4

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Abstract: RNA modifications are a common occurrence across all domains of life. Several chemical modifications, including N6- methyladenosine, have also been found in viral transcripts and viral RNA genomes. Some of the modifications increase the viral replication efficiency while also helping the virus to evade the host immune system. Nonetheless, there are numerous examples in which the host's RNA modification enzymes function as antiviral factors. Although established methods like MeRIP-seq and miCLIP can provide a transcriptome- wide overview of how viral RNA is modified, it is difficult to distinguish between the complex overlapping viral transcript isoforms using the short read-based techniques. Nanopore direct RNA sequencing (DRS) provides both long reads and direct signal readings, which may carry information about the modifications. Here, we describe a refined protocol for analyzing the RNA modifications in viral transcriptomes using nanopore technology.

Characterization of antibiotic-resistant, coagulase-negative staphylococci from fresh produce and description of Staphylococcus shinii sp. nov. isolated from chives: Gyu-Sung Cho , Bo Li , Erik Brinks , Charles , M.A.P. Franz; J. Microbiol. 2022;60(9):877-889. Published online June 22, 2022; DOI: https://doi.org/10.1007/s12275-022-2100-5

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Abstract: Coagulase-negative Staphylococcus (CoNS) species may possess antibiotic resistance genes and have been associated with nosocomial infections. In this study, 91 CoNS with decreased susceptibility to oxacillin were isolated from fresh produce using oxacillin containing agar plates. Their antibiotic resistances were determined phenotypically and all isolates were identified by rep-PCR, 16S rRNA and rpoB gene sequencing. Furthermore, the genomes of representative strains were sequenced in order to confirm species identification by phylogenomics. The majority (64 of 91) of the CoNS strains could be identified as Mammaliicoccus (M.) fleurettii, while 13 were identified as M. sciuri, 8 as M. vitulinus, 2 as Staphylococcus (S.) epidermidis and single strains each as S. warneri, S. xylosus, Staphylococcus spp. and S. casei. Most of the strains were generally susceptible to clinically-relevant antibiotics, but only few (< 7%) strains possessed multiple resistances. Both oxacillin and cefoxitin resistant isolates were considered to be presumptive methicillin-resistant CoNS. From whole genome sequencing data of 6 representative strains, the mecA gene, accessory genes and the SCC loci were compared, which revealed high variability between some of the strains. The major fatty acids of K22-5MT strain included anteiso-C15:0, iso-C15:0, iso-C17:0, anteiso-C17:0, C18:0, and C20:0. Average nucleotide identity and digital DNA-DNA hybridization values indicated that Staphylococcus strain K22-5MT was below the species delineation cutoff values for ANI (less than 91%) and DDH (less than 44.4%), with the most closely related species being the S. pseudoxylosus S04009T type strain. Thus, strain K22- 5MT (=DSM 112532T, =LMG 32324T) represents a novel species, for which the name Staphylococcus shinii sp. nov. is proposed.

Description of Flavobacterium cyclinae sp. nov. and Flavobacterium channae sp. nov., isolated from the intestines of Cyclina sinensis (Corb shell) and Channa argus (Northern snakehead): Seomin Kang , Jae-Yun Lee , Jeong Eun Han , Yun-Seok Jeong , Do-Hun Gim , Jin-Woo Bae; J. Microbiol. 2022;60(9):890-898. Published online June 22, 2022; DOI: https://doi.org/10.1007/s12275-022-2075-2

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Abstract: Two novel bacterial strains, KSM-R2A25T and KSM-R2A30T, were isolated from intestines of Cyclina sinensis (corb shell) and Channa argus (northern snakehead), respectively. Both specimens were collected in Korea. The strains were Gramstain- negative, non-motile, and strictly aerobic. According to phylogenetic analyses based on 16S rRNA gene sequences, strains belonged to the genus Flavobacterium within the family Flavobacteriaceae. 16S rRNA gene sequences of strains KSMR2A25T and KSM-R2A30T were closely related to Flavobacterium cucumis DSM 18830T and Flavobacterium aquaticum JC164T with sequence similarities of 97.77% and 98.54%, respectively. Further genomic analyses including reconstruction of the UBCG tree and overall genome-related indices suggested them as novel species of the genus Flavobacterium. Both strains contained menaquinone with six isoprene units (MK-6) as a major isoprenoid quinone and iso-C15:1 G, iso- C15:0, and iso-C16:0 as major cellular fatty acids. The major polar lipid in both strains was phosphatidylethanolamine. The genomic G + C contents of strains KSM-R2A25T and KSMR2A30T were 31.7 and 31.9%, respectively. Based on the polyphasic taxonomic study presented here, strains KSM-R2A25T and KSM-R2A30T represent novel species of the genus Flavobacterium, for which the names Flavobacterium cyclinae sp. nov and Flavobacterium channae sp. nov are proposed. The type strains of F. cyclinae sp. nov and F. channae sp. nov are KSM-R2A25T (= KCTC 82978T = JCM 34997T) and KSMR2A30T (= KCTC 82979T = JCM 34998T), respectively.

Sala cibi gen. nov., sp. nov., an extremely halophilic archaeon isolated from solar salt: Hye Seon Song , Juseok Kim , Yeon Bee Kim , Se Hee Lee , Tae Woong Whon , Seong Woon Roh; J. Microbiol. 2022;60(9):899-904. Published online July 14, 2022; DOI: https://doi.org/10.1007/s12275-022-2137-5

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Abstract: Two novel halophilic archaeal strains, CBA1133T and CBA- 1134, were isolated from solar salt in South Korea. The 16S rRNA gene sequences of the isolates were identical to each other and were closely related to the genera Natronomonas (92.3–93.5%), Salinirubellus (92.2%), Halomarina (91.3– 92.0%), and Haloglomus (91.4%). The isolated strains were coccoid, Gram-stain-negative, aerobic, oxidase-positive, and catalase-negative. Growth occurred under temperatures of 25–50°C (optimum, 45°C), NaCl levels of 10–30% (optimum, 15%), pH levels of 6.0–8.5 (optimum, 7.0), and MgCl2 concentrations of 0–500 mM (optimum, 100 mM). Digital DNADNA hybridization values between the strains and related genera ranged from 18.3% to 22.7%. The major polar lipids of the strains were phosphatidyl glycerol, phosphatidyl glycerol phosphate methyl ester, and phosphatidyl glycerol sulfate. Genomic, phenotypic, physiological, and biochemical analyses of the isolates revealed that they represent a novel genus and species in the family Halobacteriaceae. The type strain is CBA1133T (= KACC 22148T = JCM 34265T), for which the name Sala cibi gen. nov., sp. nov. is proposed.

Characterization of Marinilongibacter aquaticus gen. nov., sp. nov., a unique marine bacterium harboring four CRISPR-Cas systems in the phylum Bacteroidota: Dao-Feng Zhang , Yu-Fang Yao , Hua-Peng Xue , Zi-Yue Fu , Xiao-Mei Zhang , Zongze Shao; J. Microbiol. 2022;60(9):905-915. Published online August 1, 2022; DOI: https://doi.org/10.1007/s12275-022-2102-3

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Abstract: A novel bacterium, designated YYF0007T, was isolated from an agar-degrading co-culture. The strain was found harboring four CRISPR-Cas systems of two classes in the chromosome and subsequently subjected to a study on polyphasic taxonomy. Pairwise analyses of the 16S rRNA gene sequences indicated that strain YYF0007T had highest 16S rRNA gene sequence similarity (92.2%) to Jiulongibacter sediminis JN- 14-9T. The phylogenomic trees based on the 16S rRNA gene and 269 single-copy orthologous gene clusters (OCs) indicated that strain YYF0007T should be recognized as a novel genus of the family Spirosomaceae. The cells were Gramstain- negative, nonmotile, strictly aerobic, and straight long rods with no flagellum. Optimum growth occurred at 28°C and pH 7.0 with the presence of NaCl concentration 1.0–3.0% (w/v). The strain showed oxidase and catalase activities. The major fatty acids were C16:1ω5c, iso-C15:0 and summed feature 3 (C16:1 ω7c and/or C16:1 ω6c). The predominant isoprenoid quinone was MK-7. The complete genome size was 4.64 Mb with a DNA G + C content of 44.4%. Further typing of CRISPR-Cas systems in the family Spirosomaceae and the phylum Bacteroidota indicated that it was remarkable for strain YYF0007T featured by such a set of CRISPR-Cas systems. This trait highlights the applications of strain YYF- 0007T in studies on the evolutionary dynamics and bacterial autoimmunity of CRISPR-Cas system as a potential model. The name Marinilongibacter aquaticus gen. nov., sp. nov. is proposed, and the type strain is YYF0007T (= MCCC 1K06017T = GDMCC 1.2428T = JCM 34683T).

Complete gammaproteobacterial endosymbiont genome assembly from a seep tubeworm Lamellibrachia satsuma: Ajit Kumar Patra , Yong min Kwon , Youngik Yang; J. Microbiol. 2022;60(9):916-927. Published online August 1, 2022; DOI: https://doi.org/10.1007/s12275-022-2057-4

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Abstract: Siboglinid tubeworms thrive in hydrothermal vent and seep habitats via a symbiotic relationship with chemosynthetic bacteria. Difficulties in culturing tubeworms and their symbionts in a laboratory setting have hindered the study of host-microbe interactions. Therefore, released symbiont genomes are fragmented, thereby limiting the data available on the genome that affect subsequent analyses. Here, we present a complete genome of gammaproteobacterial endosymbiont from the tubeworm Lamellibrachia satsuma collected from a seep in Kagoshima Bay, assembled using a hybrid approach that combines sequences generated from the Illumina and Oxford Nanopore platforms. The genome consists of a single circular chromosome with an assembly size of 4,323,754 bp and a GC content of 53.9% with 3,624 protein-coding genes. The genome is of high quality and contains no assembly gaps, while the completeness and contamination are 99.33% and 2.73%, respectively. Comparative genome analysis revealed a total of 1,724 gene clusters shared in the vent and seep tubeworm symbionts, while 294 genes were found exclusively in L. satsuma symbionts such as transposons, genes for defense mechanisms, and inorganic ion transportations. The addition of this complete endosymbiont genome assembly would be valuable for comparative studies particularly with tubeworm symbiont genomes as well as with other chemosynthetic microbial communities.

Characterization of transcriptional activities at a divergent promoter of the type VI secretion system in enterohemorrhagic Escherichia coli O157:H7: Se Kye Kim , Jun Bong Lee , Jang Won Yoon; J. Microbiol. 2022;60(9):928-934. Published online August 19, 2022; DOI: https://doi.org/10.1007/s12275-022-2109-9

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Abstract: The type VI secretion system (T6SS) is a novel secretion system found in many Gram-negative bacteria that plays a role in bacterial competition, virulence, and host immune evasion. The enterohemorrhagic Escherichia coli (EHEC) O157:H7 strain EDL933 has a single functional T6SS gene cluster. In this study, we attempted to characterize the transcriptional pattern of the T6SS effector gene Z0264 in EDL933. Transcriptional analyses showed that Z0264 and other T6SS genes were transcribed in vitro in a growth-phase-dependent manner, but Z0264 was not secreted in the rich medium. Using adapter- and radioactivity-free transcription start site analysis, we identified an overlapping divergent promoter between Z0264 and Z0265. A β-galactosidase assay with truncated promoter regions showed that the divergent promoter is functional. In addition, we demonstrated the role of H-NS as a repressor in the transcription of Z0264. Notably, the cDNA PCR assay showed that the mRNA transcript from the Z0264 promoter did not include the entire main T6SS cluster, suggesting segmented gene expression by multiple promoters in the T6SS cluster. In conclusion, we identified a divergent promoter for Z0264 located in the T6SS cluster of EDL933 and characterized its in vitro transcriptional activity during growth. Our findings provide insights and a preliminary understanding of the regulatory mechanisms underlying T6SS transcription.

Activation of the SigE-SigB signaling pathway by inhibition of the respiratory electron transport chain and its effect on rifampicin resistance in Mycobacterium smegmatis: Yuna Oh , Hye-In Lee , Ji-A Jeong , Seonghan Kim , Jeong-Il Oh; J. Microbiol. 2022;60(9):935-947. Published online August 1, 2022; DOI: https://doi.org/10.1007/s12275-022-2202-0

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Abstract: Using a mutant of Mycobacterium smegmatis lacking the major aa3 cytochrome c oxidase of the electron transport chain (Δaa3), we demonstrated that inhibition of the respiratory electron transport chain led to an increase in antibiotic resistance of M. smegmatis to isoniazid, rifampicin, ethambutol, and tetracycline. The alternative sigma factors SigB and SigE were shown to be involved in an increase in rifampicin resistance of M. smegmatis induced under respiration-inhibitory conditions. As in Mycobacterium tuberculosis, SigE and SigB form a hierarchical regulatory pathway in M. smegmatis through SigE-dependent transcription of sigB. Expression of sigB and sigE was demonstrated to increase in the Δaa3 mutant, leading to upregulation of the SigB-dependent genes in the mutant. The phoU2 (MSMEG_1605) gene implicated in a phosphatesignaling pathway and the MSMEG_1097 gene encoding a putative glycosyltransferase were identified to be involved in the SigB-dependent enhancement of rifampicin resistance observed for the Δaa3 mutant of M. smegmatis. The significance of this study is that the direct link between the functionality of the respiratory electron transport chain and antibiotic resistance in mycobacteria was demonstrated for the first time using an electron transport chain mutant rather than inhibitors of electron transport chain.

Deletion of lacD gene affected stress tolerance and virulence of Streptococcus suis serotype 2: Xiaowu Jiang , Lexin Zhu , Dongbo Zhan; J. Microbiol. 2022;60(9):948-959. Published online August 19, 2022; DOI: https://doi.org/10.1007/s12275-022-2146-4

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Abstract: Streptococcus suis type 2 (S. suis type 2, SS2), an infectious pathogen which is zoonotic and can induce severely public health concern. Our previous research identified a newly differential secreted effector of tagatose-bisphosphate aldolase (LacD) mediated by VirD4 factor within the putative type IV secretion system of SS2, whereas the functional basis and roles in virulence of LacD remain elusive. Here in this study, the LacD was found enzymatic and can be activated to express under oxidative stress. Gene mutant and its complemental strain (ΔlacD and cΔlacD) were constructed to analyze the phenotypes, virulence and transcriptomic profiles as compared with the parental strain. The lacD gene deletion showed no effect on growth capability and cells morphology of SS2. However, reduced tolerance to oxidative and heat stress conditions, increased antimicrobial susceptibility to ciprofloxacin and kanamycin were found in ΔlacD strain. Further, the LacD deficiency led to weakened invasion and attenuated virulence since an easier phagocytosed and more prone to be cleared of SS2 in macrophages were shown in ΔlacD mutant. Distinctive transcriptional profiling in ΔlacD strain and typical downregulated genes with significant mRNA changes including alcohol dehydrogenase, GTPase, integrative and conjugative elements, and iron ABC transporters which were mainly involved in cell division, stress response, antimicrobial susceptibility and virulence regulation, were examined and confirmed by RNA sequencing and real time qPCR. In summary, the
results
demonstrated for the first time that LacD was a pluripotent protein mediated the metabolic, stress and virulent effect of SS2.

Enhancement of the solubility of recombinant proteins by fusion with a short-disordered peptide: Jun Ren , Suhee Hwang , Junhao Shen , Hyeongwoo Kim , Hyunjoo Kim , Jieun Kim , Soyoung Ahn , Min-gyun Kim , Seung Ho Lee , Dokyun Na; J. Microbiol. 2022;60(9):960-967. Published online July 14, 2022; DOI: https://doi.org/10.1007/s12275-022-2122-z

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Abstract: In protein biotechnology, large soluble fusion partners are widely utilized for increased yield and solubility of recombinant proteins. However, the production of additional large fusion partners poses an additional burden to the host, leading to a decreased protein yield. In this study, we identified two highly disordered short peptides that were able to increase the solubility of an artificially engineered aggregationprone protein, GFP-GFIL4, from 0.6% to 61% (D3-DP00592) and 46% (D4-DP01038) selected from DisProt database. For further confirmation, the peptides were applied to two insoluble E. coli proteins (YagA and YdiU). The peptides also enhanced solubility from 52% to 90% (YagA) and from 27% to 93% (YdiU). Their ability to solubilize recombinant proteins was comparable with strong solubilizing tags, maltosebinding protein (40 kDa) and TrxA (12 kDa), but much smaller (< 7 kDa) in size. For practical application, the two peptides were fused with a restriction enzyme, I-SceI, and they increased I-SceI solubility from 24% up to 75%. The highly disordered peptides did not affect the activity of I-SceI while I-SceI fused with MBP or TrxA displayed no restriction activity. Despite the small size, the highly disordered peptides were able to solubilize recombinant proteins as efficiently as conventional fusion tags and did not interfere with the function of recombinant proteins. Consequently, the identified two highly disordered peptides would have practical utility in protein biotechnology and industry.

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