Zhizhuo Shao,Menglin Guo,Hong Wang,Wenhui Gu,Xiujun Xie,Guangce Wang
Pyropia yezoensis is an important intertidal economic macroalgae, which is periodically affected by various stresses, such as the limitation of inorganic carbon (C i ) deficiency. Under such environment, the redox homeostasis within the cells of Pyropia yezoensis is seriously affected, and the reactive oxygen species (ROS) signal transduction system would be activated to regulate the photosynthetic activity. Therefore, how P. yezoensis manage ROS to maintain effective photosynthetic carbon fixation has aroused great interest. Here, we characterize transformants overexpressing respiratory burst oxidase homolog ( Rboh ), an important gene that can actively produce ROS, at the levels of cellular physiology, biochemistry, and transcriptomics. Our data indicated the expression of Rboh significantly increased, accompanied by a significant upregulated expression of alpha-type carbonic anhydrase 3 (α CA3 ) and increased extracellular carbonic anhydrase activity in the Rboh overexpressing strains. Interestingly, compared with the wild type, the photosynthetic activity of transgenic strains was significantly higher under the low C i and high light condition, implying that the ROS signal triggered by overexpression of Rboh was involved in regulating the C i absorption and utilization in P. yezoensis when the C i source was limited. In summary, this study provided evidence supporting the correlation between the ROS production and the Ci utilization under stress environments in P. yezoensis .
The secretion of ligninolytic enzyme provides a competitive advantage for microbial survival. These enzymes are commonly transported to the extracellular milieu via signal peptides for the catabolism of lignin, which cannot be translocated through the cell membrane. However, some bacterial ligninolytic enzymes lack signal peptides, yet they can still be secreted. It remains unclear how these unconventional proteins cross the cell membrane. Here, we reveal a secretion mechanism for the unconventional B-type dye-decolorizing peroxidase (DypB) in Pseudomonas putida A514. Type VI secretion system (T6SS) mediates the inner membrane channel, where interaction of DypB with the T6SS components VgrG and Hcp accounts for periplasmic delivery. Once in the periplasm, DypB is allocated into outer membrane vesicles (OMVs) and released to the extracellular space. The crosslinked translocation model for DypB delivery represents an ingenious mechanism by which bacteria harness extant systems to thrive in a nutrient-poor environment. Moreover, we develop an OMV-surface display platform to improve DypB secretion and further enhance lignin utilization, exemplifying the applicability of OMVs as a lignin biocatalytic nanoreactor. Our study demonstrates the previously unrecognized crosslinking of T6SS and OMVs for the secretion of unconventional ligninolytic peroxidase and provides new perspectives on its biotechnological applications.
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