Journal of Microbiology

Journal Articles

Gene deletion and constitutive expression of the pectate lyase gene 1 (MoPL1) lead to diminished virulence of Magnaporthe oryzae: Alex Wegner , Florencia Casanova , Marco Loehrer , Angelina Jordine , Stefan Bohnert , Xinyu Liu , Zhengguang Zhang , Ulrich Schaffrath; J. Microbiol. 2022;60(1):79-88. Published online December 29, 2021; DOI: https://doi.org/10.1007/s12275-022-1074-7

Abstract: Phytopathogenic fungi are known to secrete specific proteins which act as virulence factors and promote host colonization. Some of them are enzymes with plant cell wall degradation capability, like pectate lyases (Pls). In this work, we examined the involvement of Pls in the infection process of Magnaporthe oryzae, the causal agent of rice blast disease. From three Plgenes annotated in the M. oryzae genome, only transcripts of MoPL1 considerably accumulated during the infection process with a peak at 72 h post inoculation. Both, gene deletion and a constitutive expression of MoPL1 in M. oryzae led to a significant reduction in virulence. By contrast, mutants that constitutively expressed an enzymatic inactive version of MoPl1 did not differ in virulence compared to the wild type isolate. This indicates that the enzymatic activity of MoPl1 is responsible for diminished virulence, which is presumably due to degradation products recognized as danger associated molecular patterns (DAMPs), which strengthen the plant immune response. Microscopic analysis of infection sites pointed to an increased plant defense response. Additionally, MoPl1 tagged with mRFP, and not the enzymatic inactive version, focally accumulated in attacked plant cells beneath appressoria and at sites where fungal hyphae transverse from one to another cell. These findings shed new light on the role of pectate lyases during tissue colonization in the necrotrophic stage of M. oryzae's life cycle.

Influences of genetically perturbing synthesis of the typical yellow pigment on conidiation, cell wall integrity, stress tolerance, and cellulase production in Trichoderma reesei: Weixin Zhang , Ning An , Junqi Guo , Zhixing Wang , Xiangfeng Meng , Weifeng Liu; J. Microbiol. 2021;59(4):426-434. Published online January 26, 2021; DOI: https://doi.org/10.1007/s12275-021-0433-0

Abstract: The prominent protein producing workhorse Trichoderma reesei secretes a typical yellow pigment that is synthesized by a gene cluster including two polyketide synthase encoding genes sor1 and sor2. Two transcription factors (YPR1 and YPR2) that are encoded in the same cluster have been shown to regulate the expression of the sor genes. However, the physiological relevance of the yellow pigment synthesis in T. reesei is not completely clear. In this study, a yellow pigment hyper-producer OEypr1 and three yellow pigment non-producers, OEypr1-sor1, Δypr1, and OEypr2, were constructed. Their phenotypic features in mycelial growth, conidiation, cell wall integrity, stress tolerance, and cellulase production were determined. Whereas hyperproduction of the yellow pigment caused significant defects in all the physiological aspects tested, the non-producers showed similar colony growth, but improved conidiation, maintenance of cell wall integrity, and stress tolerance compared to the control strain. Moreover, in contrast to the severely compromised extracellular cellobiohydrolase production in the yellow pigment hyperproducer, loss of the yellow pigment hardly affected induced cellulase gene expression. Our results demonstrate that interfering with the yellow pigment synthesis constitutes an engineering strategy to endow T. reesei with preferred features for industrial application.

Mutants defective in the production of encapsulin show a tan-phaselocked phenotype in Myxococcus xanthus: Dohee Kim , Juo Choi , Sunjin Lee , Hyesook Hyun , Kyoung Lee , Kyungyun Cho; J. Microbiol. 2019;57(9):795-802. Published online June 11, 2019; DOI: https://doi.org/10.1007/s12275-019-8683-9

Abstract: Myxococcus xanthus, a myxobacterium, displays phase variation between yellow phase and tan phase. We found that deletion of the encA gene encoding encapsulin and the encF gene encoding a metalloprotease causes formation of tan colonies that never transform into yellow colonies. The encA and encF mutants were defective in the production of DKxanthene and myxovirescin. They did not produce extracellular polysaccharides; hence, the cells did not aggregate in liquid and showed reduced swarming on agar plates. The mutants had defective sporulation, but were rescued extracellularly by wild type cells. All these traits indicate that the encA and encF mutants are likely to be tan-phase-locked, and encapsulin has a close relationship with phase variation in M. xanthus. The encA and encF genes are localized in the same gene cluster, encBAEFG (MXAN_3557~MXAN_3553). Unlike the encA and encF genes, deletion of other genes in the cluster did not show tan-phase-locked phenotype.

Research Support, Non-U.S. Gov't

Effects of Exopolysaccharide Production on Liquid Vegetative Growth, Stress Survival, and Stationary Phase Recovery in Myxococcus xanthus: Wei Hu , Jing Wang , Ian McHardy , Renate Lux , Zhe Yang , Yuezhong Li , Wenyuan Shi; J. Microbiol. 2012;50(2):241-248. Published online April 27, 2012; DOI: https://doi.org/10.1007/s12275-012-1349-5

Abstract: Exopolysaccharide (EPS) of Myxococcus xanthus is a wellregulated cell surface component. In addition to its known functions for social motility and fruiting body formation on solid surfaces, EPS has also been proposed to play a role in multi-cellular clumping in liquid medium, though this phenomenon has not been well studied. In this report, we confirmed that M. xanthus clumps formed in liquid were correlated with EPS levels and demonstrated that the EPS encased cell clumps exhibited biofilm-like structures. The clumps protected the cells at physiologically relevant EPS concentrations, while cells lacking EPS exhibited significant reduction in long-term viability and resistance to stressful conditions. However, excess EPS production was counterproductive to vegetative growth and viable cell recovery declined in extended late stationary phase as cells became trapped in the matrix of clumps. Therefore, optimal EPS production by M. xanthus is important for normal physiological functions in liquid.

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