Comparative Phenotypic Analysis of Anabaena sp. PCC 7120 Mutants of Porinlike Genes

Abstract

Porins are essential for the viability of Gram-negative bacteria. They ensure the uptake of nutrients, can be involved in the maintenance of outer membrane integrity and define the antibiotic or drug resistance of organisms. The function and structure of porins in proteobacteria is well described, while their function in photoautotrophic cyanobacteria has not been systematically explored. We compared the domain architecture of nine putative porins in the filamentous cyanobacterium Anabaena sp. PCC 7120 and analyzed the seven candidates with predicted OprB-domain. Single recombinant mutants of the seven genes were created and their growth capacity under different conditions was analyzed. Most of the putative porins seem to be involved in the transport of salt and copper, as respective mutants were resistant to elevated concentrations of these substances. In turn, only the mutant of alr2231 was less sensitive to elevated zinc concentrations, while mutants of alr0834 , alr4741 and all4499 were resistant to high manganese concentrations. Notably the mutant of alr4550 shows a high sensitivity against harmful compounds, which is indicative for a function related to the maintenance of outer membrane integrity. Moreover, the mutant of all5191 exhibited a phenotype which suggests either a higher nitrate demand or an inefficient nitrogen fixation. The dependency of porin membrane insertion on Omp85 proteins was tested exemplarily for Alr4550, and an enhanced aggregation of Alr4550 was observed in two omp85 mutants. The comparative analysis of porin mutants suggests that the proteins in parts perform distinct functions related to envelope integrity and solute uptake.

Evolutionary genomic insights into cyanobacterial symbioses in plants

“…Additionally, some mutants of porin-like genes from Anabaena sp. PCC 7120 had altered phenotypes of the outer membrane, affected integration of other porins in the membrane or affected nitrogen demand and/or fixation (Schätzle et al, 2021). Hence, the OprB family appears to have a diversity of roles in bacterial biology; however, whether the role of OprB in sugar uptake is primary or a secondary effect cannot be distinguished because membrane integrity or integration of other proteins into the membrane was not assessed by Ekman et al in 2013. In agreement with the data from Khamar et al (2010), all mutants for the fructose and glucose transporters were able to form hormogonia (Ekman et al, 2013).…”

“…Functional analyses of the genome of the symbiotic N. punctiforme showed that it encodes a functional fructose transporter, a glucose permease and an OprB family porin, which was associated with the uptake of both sugars (Ekman et al, 2013 ). In other cyanobacteria, this porin family has recently been associated with transport of different metals (Qiu et al, 2021 ; Schätzle et al, 2021 ). Additionally, some mutants of porin-like genes from Anabaena sp.…”

FurC (PerR) contributes to the regulation of peptidoglycan remodeling and intercellular molecular transfer in the cyanobacterium Anabaena sp. strain PCC 7120

“…2 ; Table S2). This group includes several porin-like proteins, namely the major outer membrane proteins Alr0834 (OprB-1), Alr4741, Alr7614, Alr4893, All4499, Alr4550, and Alr2269 (Omp85) ( 13 , 32 , 33 ); the outer membrane TolC transporter homolog HgdD (Alr2887) ( 34 ); the N-acetylmuramyl-L-alanine amidases AmiC1, AmiC2, and All4999 ( 35 , 36 ); and LptA (Alr4067), a protein of the lipopolysaccharide export system to the outer membrane ( 37 ), among others. Finally, it is noteworthy the strong decrease in the two-component hybrid sensor and regulator All1178 (−451.68-fold), whose function is unknown, and the FurA paralog ( 38 ) (−87.48-fold).…”

A cobalt concentration sensitive Btu-like system facilitates cobalamin uptake in Anabaena sp. PCC 7120

“…In response to this, different uptake systems and pathways have evolved and their components are encoded in the genomes of cyanobacteria. The transport of solutes involves, for example, porins for salt and other nutrients (e.g., [ 1 – 3 ]). Solutes that exceed the diffusion size of porins or have a very low abundance in the environment are actively transported by specialized systems (e.g., [ 4 ]).…”