Improving acid resistance of Escherichia coli base on the CfaS-mediated membrane engineering strategy derived from extreme acidophile.

Industrial microorganisms used for the production of organic acids often face challenges such as inhibited cell growth and reduced production efficiency due to the accumulation of acidic metabolites. One promising way for improving the acid resistance of microbial cells is to reconstruct their membranes. Herein, the overexpression of cfa2 from extreme acidophile endowed E. coli with high-performance on resistance to the acid stress. The engineered strain M1-93-Accfa2, constructed by CRISPR/Cas9-mediated chromosome integration, also exhibited a significantly higher resistance to severe acid stress. The analysis of fatty acid profiles indicated that the proportion of Cy-19:0 in the cell membrane of M1-93-Accfa2 increased by 5.26 times compared with the control, while the proportion of C18:1w9c decreased by 5.81 times. Correspondingly, the permeability and fluidity of the membrane decreased significantly. HPLC analysis demonstrated that the contents of intracellular glutamic acid, arginine, methionine and aspartic acid of M1-93-Accfa2 were 2.59, 2.04, 22.07 and 2.65 times that of the control after environmental acidification, respectively. Meanwhile, transmission electron microscopy observation indicated that M1-93-Accfa2 could maintain a plumper cell morphology after acid stimulation. M1-93-Accfa2 also exhibited higher-performance on the resistance to organic acids, especially succinic acid stress. These results together demonstrated the great potential of M1-93-Accfa2 constructed here in the production of organic acids.

Co-occurrence of chromophytic phytoplankton and the Vibrio community during Phaeocystis globosa blooms in the Beibu Gulf.

Accumulating research evidence has revealed that harmful algal blooms (HABs) can substantially affect the community structures of phytoplankton and heterotrophic bacteria in marine ecosystems. However, little is known about their species-specific interactions between phytoplankton and heterotrophic bacteria during the HABs period and about their interaction shifts in response to blooms. From this perspective, we investigated the co-occurrence of chromophytic phytoplankton and Vibrio during Phaeocystis globosa blooms in the Beibu Gulf. The results showed that Vibrio communities were distinct during the blooms, and P. globosa blooms resulted in a decline in phytoplankton alpha diversity, revealing that the blooms could affect their community compositions. The regression lines between the Shannon indices and Bray-Curtis distances of phytoplankton and Vibrio showed positive correlations with each other (p < 0.001), suggesting that they may have intrageneric symbiotic interactions overall. In addition, network analysis further demonstrated that relationships between phytoplankton and Vibrio were dominated by positive correlations, and more interaction modules were observed during the blooms, revealing that the blooms intensified synergistic association and mutual symbiotic interactions between them. Environmental factors (SiO32-, NH4+, NO3- and TN,) and P. globosa density more deeply affected network interactions between phytoplankton and Vibrio during the periods of P. globosa blooms than those before the blooms and after the blooms. This study provided new insight to elucidate community structure and interaction relationships between phytoplankton and Vibrio in response to P. globosa blooms and their ecological effects in marine ecosystems.