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- Iron interferes with quorum sensing-mediated cooperation in Pseudomonas aeruginosa by affecting the expression of ppyR and mexT, in addition to rhlR
- Feng Sun , Na Li , Lijia Wang , Huajun Feng , Dongsheng Shen , Meizhen Wang
- J. Microbiol. 2020;58(11):938-944. Published online October 30, 2020
- DOI: https://doi.org/10.1007/s12275-020-0264-4
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- 4 Citations
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Abstract
- The stabilization of quorum sensing (QS) is vital for bacterial survival in various environments. Although the mechanisms of QS stabilization in certain conditions have been well studied, the impact of environmental factors has received much less attention. In this study, we show that the supplementation of 25 μM iron in competition experiments and 50 μM in evolution experiments to casein growth cultures significantly increased the possibility of population collapse by affecting elastase production. However, the expression of lasI and lasR remained constant regardless of iron concentration and hence this effect was not through interference with the LasIR circuit, which mainly regulates the secretion of elastase in Pseudomonas aeruginosa. However, the expression of rhlR was significantly inhibited by iron treatment, which could affect the production of elastase. Further, based on both reverse transcription quantitative polymerase chain reaction and gene knock-out assays, we show that iron inhibits the transcription of ppyR and enhances the expression of mexT, both of which decrease elastase production and correspondingly interfere with QS stabilization. Our findings show that environmental factors can affect the genes of QS circuits, interfering with QS stabilization. These findings are not only beneficial in understanding the mechanistic effect of iron on QS stabilization, but also demonstrate the complexity of QS stabilization by linking non-QS-related genes with QS traits.
- The effects of deletion of cellobiohydrolase genes on carbon source-dependent growth and enzymatic lignocellulose hydrolysis in Trichoderma reesei
- Meibin Ren , Yifan Wang , Guoxin Liu , Bin Zuo , Yuancheng Zhang , Yunhe Wang , Weifeng Liu , Xiangmei Liu , Yaohua Zhong
- J. Microbiol. 2020;58(8):687-695. Published online June 10, 2020
- DOI: https://doi.org/10.1007/s12275-020-9630-5
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- 7 Citations
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Abstract
- The saprophytic fungus Trichoderma reesei has long been used as a model to study microbial degradation of lignocellulosic biomass. The major cellulolytic enzymes of T. reesei are the cellobiohydrolases CBH1 and CBH2, which constitute more than 70% of total proteins secreted by the fungus. However, their physiological functions and effects on enzymatic hydrolysis of cellulose substrates are not sufficiently elucidated. Here, the cellobiohydrolase-encoding genes cbh1 and cbh2 were deleted, individually or combinatively, by using an auxotrophic marker-recycling technique in T. reesei. When cultured on media with different soluble carbon sources, all three deletion strains (Δcbh1, Δcbh2, and Δcbh1Δcbh2) exhibited no dramatic variation in morphological phenotypes, but their growth rates increased apparently when cultured on soluble cellulase-inducing carbon sources. In addition, Δcbh1 showed dramatically reduced growth and Δcbh1Δcbh2 could hardly grew on microcrystalline cellulose (MCC), whereas all strains grew equally on sodium carboxymethyl cellulose (CMC-Na), suggesting that the influence of the CBHs on growth was carbon source-dependent. Moreover, five representative cellulose substrates were used to analyse the influence of the absence of CBHs on saccharification efficiency. CBH1 deficiency significantly affected the enzymatic hydrolysis rates of various cellulose substrates, where acid pre-treated corn stover (PCS) was influenced the least. CBH2 deficiency reduced the hydrolysis of MCC, PCS, and acid pre-treated and delignified corncob but improved the hydrolysis ability of filter paper. These results demonstrate the specific contributions of CBHs to the hydrolysis of different types of biomass, which could facilitate the development of tailor-made strains with highly efficient hydrolysis enzymes for certain biomass types in the biofuel industry.
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