Journal of Microbiology

Volume 58(7); July 2020

Review

[MINIREVIEW]Bacterial bug-out bags: outer membrane vesicles and their proteins and functions: Kesavan Dineshkumar , Vasudevan Aparna , Liang Wu , Jie Wan , Mohamod Hamed Abdelaziz , Zhaoliang Su , Shengjun Wang , Huaxi Xu; J. Microbiol. 2020;58(7):531-542. Published online June 10, 2020; DOI: https://doi.org/10.1007/s12275-020-0026-3

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Abstract: Among the major bacterial secretions, outer membrane vesicles (OMVs) are significant and highly functional. The proteins and other biomolecules identified within OMVs provide new insights into the possible functions of OMVs in bacteria. OMVs are rich in proteins, nucleic acids, toxins and virulence factors that play a critical role in bacteria-host interactions. In this review, we discuss some proteins with multifunctional features from bacterial OMVs and their role involving the mechanisms of bacterial survival and defence. Proteins with moonlighting activities in OMVs are discussed based on their functions in bacteria. OMVs harbour many other proteins that are important, such as proteins involved in virulence, defence, and competition. Overall, OMVs are a power-packed aid for bacteria, harbouring many defensive and moonlighting proteins and acting as a survival kit in
case
of an emergency or as a defence weapon. In summary, OMVs can be defined as bug-out bags for bacterial defence and, therefore, survival.

Journal Articles

Azohydromonas aeria sp. nov., isolated from air: Han Xue , Chun-gen Piao , Dan-ran Bian , Min-wei Guo , Yong Li; J. Microbiol. 2020;58(7):543-549. Published online June 27, 2020; DOI: https://doi.org/10.1007/s12275-020-9423-x

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Abstract: A grey pink colored bacterium, strain t3-1-3T, was isolated from the air at the foot of the Xiangshan Mountain in Beijing, China. The cells are aerobic, Gram-stain-negative, non-sporeforming, motile and coccoid-rod shaped (0.9–1.2 × 1.9–2.1 μm). Strain t3-1-3T was catalase-positive and oxidase-negative and this strain grew at 4–42°C (optimum 28°C), a pH of 4.0–9.0 (optimum pH 7.0) and under 0–2% (w/v) NaCl (optimum 0–1% NaCl). A phylogenetic analysis based on 16S rRNA gene sequences revealed that strain t3-1-3T was closely related to Azohydromonas riparia UCM-11T (97.4% similarity), followed by Azohydromonas australica G1-2T (96.8%) and Azohydromonas ureilytica UCM-80T (96.7%). The genome of strain t3-1-3T contains 6,895 predicted protein-encoding genes, 8 rRNA genes, 62 tRNA genes and one sRNA gene, as well as five potential biosynthetic gene clusters, including clusters of genes coding for non-ribosomal peptide synthetase (NRPS), bacteriocin and arylpolyene and two clusters of genes for terpene. The predominant cellular fatty acids (> 10.0% of the total) in strain t3-1-3T were summed feature 3 (C16:1ω7c and/or C16:1ω6c, 37.8%), summed feature 8 (C18:1ω7c and/or C18:1ω6c, 29.7%) and C16:0 (17.3%). Strain t3-1-3T contained ubiquinone-8 (Q-8) as the predominant respiratory quinone. The polar lipids of strain t3-1-3T comprised phosphatidyl ethanolamine (PE), phosphatidyl glycerol (PG), diphosphatidyl glycerol (DPG), an unidentified glycolipid (GL), an unidentified aminophospholipid (APL), two unidentified phospholipid (PL1-2) and five unidentified lipid (L1-5). The DNA G + C content of the type strain is 70.3%. The broader range of growth temperature, assimilation of malic acid and trisodium citrate, presence of C18:3ω6c and an unidentified glycolipid and absence of C12:0 2-OH and C16:0iso differentiate strain t3-1-3T from related species. Based on the taxonomic data presented in this study, we suggest that strain t3-1-3T represents a novel species within the genus Azohydromonas, for which the name Azohydromonas aeria sp. nov. is proposed. The type strain of Azohydromonas aeria is t3-1-3T (= CFCC 13393T = LMG 30135T).

Burkholderia thailandensis outer membrane vesicles exert antimicrobial activity against drug-resistant and competitor microbial species: Yihui Wang , Joseph P. Hoffmann , Chau-Wen Chou , Kerstin Höner zu Bentrup , Joseph A. Fuselier , Jacob P. Bitoun , William C. Wimley , Lisa A. Morici; J. Microbiol. 2020;58(7):550-562. Published online April 11, 2020; DOI: https://doi.org/10.1007/s12275-020-0028-1

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37 Citations

Abstract: Gram-negative bacteria secrete outer membrane vesicles (OMVs) that play critical roles in intraspecies, interspecies, and bacteria-environment interactions. Some OMVs, such as those produced by Pseudomonas aeruginosa, have previously been shown to possess antimicrobial activity against competitor species. In the current study, we demonstrate that OMVs from Burkholderia thailandensis inhibit the growth of drug-sensitive and drug-resistant bacteria and fungi. We show that a number of antimicrobial compounds, including peptidoglycan hydrolases, 4-hydroxy-3-methyl-2-(2-nonenyl)- quinoline (HMNQ) and long-chain rhamnolipid are present in or tightly associate with B. thailandensis OMVs. Furthermore, we demonstrate that HMNQ and rhamnolipid possess antimicrobial and antibiofilm properties against methicillin- resistant Staphylococcus aureus (MRSA). These findings indicate that B. thailandensis secretes antimicrobial OMVs that may impart a survival advantage by eliminating competition. In addition, bacterial OMVs may represent an untapped resource of novel therapeutics effective against biofilm- forming and multidrug-resistant organisms.

Long-term continuously monocropped peanut significantly disturbed the balance of soil fungal communities: Mingna Chen , Jiancheng Zhang , Hu Liu , Mian Wang , LiJuan Pan , Na Chen , Tong Wang , Yu Jing , Xiaoyuan Chi , Binghai Du; J. Microbiol. 2020;58(7):563-573. Published online April 22, 2020; DOI: https://doi.org/10.1007/s12275-020-9573-x

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Abstract: Balancing soil microbial diversity and abundance is critical to sustaining soil health, and understanding the dynamics of soil microbes in a monocropping system can help determine how continuous monocropping practices induce soil sickness mediated by microorganisms. This study used previously constructed gradient continuous monocropping plots and four varieties with different monocropping responses were investigated. The feedback responses of their soil fungal communities to short-term and long-term continuous monocropping were tracked using high-throughput sequencing techniques. The analyses indicated that soil samples from 1 and 2 year monocropped plots were grouped into one class, and samples from the 11 and 12 year plots were grouped into another, regardless of variety. At the species level, the F. solani, Fusarium oxysporum, Neocosmospora striata, Acrophialophora levis, Aspergillus niger, Aspergillus corrugatus, Thielavia hyrcaniae, Emericellopsis minima, and Scedosporium aurantiacum taxa showed significantly increased abundances in the long-term monocropping libraries compared to the short-term cropping libraries. In contrast, Talaromyces flavus, Talaromyces purpureogenus, Mortierella alpina, Paranamyces uniporus, and Volutella citrinella decreased in the long-term monocropping libraries compared to the shortterm libraries. This study, combined with our previous study, showed that fungal community structure was significantly affected by the length of the monocropping period, but peanut variety and growth stages were less important. The increase in pathogen abundances and the decrease in beneficial fungi abundances seem to be the main cause for the yield decline and poor growth of long-term monocultured peanut. Simplification of fungal community diversity could also contribute to peanut soil sickness under long-term monocropping. Additionally, the different responses of peanut varieties to monocropping may be related to variations in their microbial community structure.

The putative C2H2 transcription factor RocA is a novel regulator of development and secondary metabolism in Aspergillus nidulans: Dong Chan Won , Yong Jin Kim , Da Hye Kim , Hee-Moon Park , Pil Jae Maeng; J. Microbiol. 2020;58(7):574-587. Published online April 22, 2020; DOI: https://doi.org/10.1007/s12275-020-0083-7

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Abstract: Multiple transcriptional regulators play important roles in the coordination of developmental processes, including asexual and sexual development, and secondary metabolism in the filamentous fungus Aspergillus nidulans. In the present study, we characterized a novel putative C2H2-type transcription factor (TF), RocA, in relation to development and secondary metabolism. Deletion of rocA increased conidiation and caused defective sexual development. In contrast, the overexpression of rocA exerted opposite effects on both phenotypes. Additionally, nullifying rocA resulted in enhanced brlA expression and reduced nsdC expression, whereas its overexpression exerted the opposite effects. These results suggest that RocA functions as a negative regulator of asexual development by repressing the expression of brlA encoding a key asexual development activator, but as a positive regulator of sexual development by enhancing the expression of nsdC encoding a pivotal sexual development activator. Deletion of rocA increased the production of sterigmatocystin (ST), as well as the expression of its biosynthetic genes, aflR and stcU. Additionally, the expression of the biosynthetic genes for penicillin (PN), ipnA and acvA, and for terrequinone (TQ), tdiB and tdiE, was increased by rocA deletion. Thus, it appears that RocA functions as a negative transcriptional modulator of the secondary metabolic genes involved in ST, PN, and TQ biosynthesis. Taken together, we propose that RocA is a novel transcriptional regulator that may act either positively or negatively at multiple target genes necessary for asexual and sexual development and secondary metabolism.

Melatonin attenuates microbiota dysbiosis of jejunum in short-term sleep deprived mice: Ting Gao , Zixu Wang , Jing Cao , Yulan Dong , Yaoxing Chen; J. Microbiol. 2020;58(7):588-597. Published online May 18, 2020; DOI: https://doi.org/10.1007/s12275-020-0094-4

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27 Citations

Abstract: Our study demonstrated that sleep deprivation resulted in homeostasis disorder of colon. Our study goes deeper into the positive effects of melatonin on small intestinal microbiota disorder caused by sleep deprivation. We successfully established a multiplatform 72 h sleep deprivation mouse model with or without melatonin supplementation, and analyzed the change of small intestinal microbiota using high-throughput sequencing of the 16S rRNA. We found melatonin supplementation suppressed the decrease of plasma melatonin level in sleep deprivation mice. Meanwhile, melatonin supplementation improved significantly the reduction in OTU numbers and the diversity and richness of jejunal microbiota and the abundance of Bacteroidaeae and Prevotellaceae, as well as an increase in the Firmicutes-to-Bacteroidetes ratio and the content of Moraxellaceae and Aeromonadaceae in the jejunum of sleep deprived-mice. Moreover, melatonin supplementation reversed the change of metabolic pathway in sleep deprived-mice, including metabolism, signal transduction mechanisms and transcription etc, which were related to intestinal health. Furthermore, melatonin supplementation inverted the sleep deprivation-induced a decline of anti-inflammatory cytokines (IL-22) and an increase of the ROS and proinflammatory cytokines (IL-17) in jejunum. These findings suggested that melatonin, similar to a probiotics agent, can reverse sleep deprivation-induced small intestinal microbiota disorder by suppressing oxidative stress and inflammation response.

Phenotypic characterization of a conserved inner membrane protein YhcB in Escherichia coli: Chul Gi Sung , Umji Choi , Chang-Ro Lee; J. Microbiol. 2020;58(7):598-605. Published online April 22, 2020; DOI: https://doi.org/10.1007/s12275-020-0078-4

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Abstract: Although bacteria have diverse membrane proteins, the function of many of them remains unknown or uncertain even in Escherichia coli. In this study, to investigate the function of hypothetical membrane proteins, genome-wide analysis of phenotypes of hypothetical membrane proteins was performed under various envelope stresses. Several genes responsible for adaptation to envelope stresses were identified. Among them, deletion of YhcB, a conserved inner membrane protein of unknown function, caused high sensitivities to various envelope stresses and increased membrane permeability, and caused growth defect under normal growth conditions. Furthermore, yhcB deletion resulted in morphological aberration, such as branched shape, and cell division defects, such as filamentous growth and the generation of chromosome- less cells. The analysis of antibiotic susceptibility showed that the yhcB mutant was highly susceptible to various anti-folate antibiotics. Notably, all phenotypes of the yhcB mutant were completely or significantly restored by YhcB without the transmembrane domain, indicating that the localization of YhcB on the inner membrane is dispensable for its function. Taken together, our results demonstrate that YhcB is involved in cell morphology and cell division in a membrane localization-independent manner.

Structural and sequence comparisons of bacterial enoyl-CoA isomerase and enoyl-CoA hydratase: Jisub Hwang , Chang-Sook Jeong , Chang Woo Lee , Seung Chul Shin , Han-Woo Kim , Sung Gu Lee , Ui Joung Youn , Chang Sup Lee , Tae-Jin Oh , Hak Jun Kim , Hyun Park , Hyun Ho Park , Jun Hyuck Lee; J. Microbiol. 2020;58(7):606-613. Published online April 22, 2020; DOI: https://doi.org/10.1007/s12275-020-0089-1

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Abstract: Crystal structures of enoyl-coenzyme A (CoA) isomerase from Bosea sp. PAMC 26642 (BoECI) and enoyl-CoA hydratase from Hymenobacter sp. PAMC 26628 (HyECH) were determined at 2.35 and 2.70 Å resolution, respectively. BoECI and HyECH are members of the crotonase superfamily and are enzymes known to be involved in fatty acid degradation. Structurally, these enzymes are highly similar except for the orientation of their C-terminal helix domain. Analytical ultracentrifugation was performed to determine the oligomerization states of BoECI and HyECH revealing they exist as trimers in solution. However, their putative ligand-binding sites and active site residue compositions are dissimilar. Comparative sequence and structural analysis revealed that the active site of BoECI had one glutamate residue (Glu135), this site is occupied by an aspartate in some ECIs, and the active sites of HyECH had two highly conserved glutamate residues (Glu118 and Glu138). Moreover, HyECH possesses a salt bridge interaction between Glu98 and Arg152 near the active site. This interaction may allow the catalytic Glu118 residue to have a specific conformation for the ECH enzyme reaction. This salt bridge interaction is highly conserved in known bacterial ECH structures and ECI enzymes do not have this type of interaction. Collectively, our comparative sequential and structural studies have provided useful information to distinguish and classify two similar bacterial crotonase superfamily enzymes.

Endophytic bacterial and fungal microbiota in different cultivars of cassava (Manihot esculenta Crantz): Hong Li , Chengliang Yan , Yanqiong Tang , Xiang Ma , Yinhua Chen , Songbi Chen , Min Lin , Zhu Liu; J. Microbiol. 2020;58(7):614-623. Published online May 18, 2020; DOI: https://doi.org/10.1007/s12275-020-9565-x

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Abstract: Endophytes colonize tissues of healthy host plants and play a crucial role in plant growth and development. However, little attention has been paid to the endophytes of tuber crops such as cassava, which is used as a staple food by approximately 800 million people worldwide. This study aimed to elucidate the diversity and composition of endophytic bacterial and fungal communities in different cassava cultivars using high-throughput sequencing. Although no significant differences in richness or diversity were observed among the different cassava cultivars, the community compositions were diverse. Two cultivars (SC124 and SC205) tolerant to root rot exhibited similar community compositions, while two other cultivars (SC10 and SC5), which are moderately and highly susceptible to root rot, respectively, harboured similar community compositions. Proteobacteria, Firmicutes, and Ascomycota dominated the endophyte assemblages, with Weissella, Serratia, Lasiodiplodia, Fusarium, and Diaporthe being the predominant genera. The differentially abundant taxonomic clades between the tolerant and susceptible cultivars were mainly rare taxa, such as Lachnoclostridium_5, Rhizobium, Lampropedia, and Stenotrophomonas. These seemed to be key genera that affected the susceptibility of cassava to root rot. Moreover, the comparison of KEGG functional profiles revealed that ‘Environmental adaptation’ category was significantly enriched in the tolerant cultivars, while ‘Infectious diseases: Parasitic’ category was significantly enriched in the susceptible cultivars. The present findings open opportunities for further studies on the roles of endophytes in the susceptibility of plants to diseases.

Phosphorylation of tegument protein pp28 contributes to trafficking to the assembly compartment in human cytomegalovirus infection: Jun-Young Seo , Jin Ah Heo , William J. Britt; J. Microbiol. 2020;58(7):624-631. Published online June 27, 2020; DOI: https://doi.org/10.1007/s12275-020-0263-5

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Abstract: Human cytomegalovirus (HCMV) UL99 encodes a late tegument protein pp28 that is essential for envelopment and production of infectious virus. This protein is localized to the endoplasmic reticulum-Golgi intermediate compartment (ERGIC) in transfected cells but it localizes to the cytoplasmic assembly compartment (AC) in HCMV-infected cells. Trafficking of pp28 to the AC is required for the assembly of infectious virus. The N-terminal domain (aa 1-61) of pp28 is sufficient for trafficking and function of the wild type protein during viral infection. However, residues required for authentic pp28 trafficking with the exception of the acidic cluster in the N-terminal domain of pp28 remain undefined. Monitoring protein migration on SDS-PAGE, we found that pp28 is phosphorylated in the virus-infected cells and dephosphorylated in the viral particles. By generating substitution mutants of pp28, we showed that three serine residues (aa 41–43) and a tyrosine residue (aa 34) account for its phosphorylation. The mutant forms of pp28 were localized to the plasma membrane as well as the ERGIC in transfected cells. Likewise, these mutant proteins were localized to the plasma membrane as well as the AC in virus-infected cells. These results suggested that phosphorylation of pp28 contributes to its intracellular trafficking and efficient viral assembly and incorporation.

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