The outer membrane of a heterocyst‐forming cyanobacterium is a permeability barrier for uptake of metabolites that are exchanged between cells

Abstract

The multicellular Anabaena sp. strain PCC 7120 is a filamentous cyanobacterium that can fix N(2) in differentiated cells called heterocysts, which exchange nutritional and regulatory compounds with the neighbour photosynthetic vegetative cells. The outer membrane of this bacterium is continuous along the filament defining a continuous periplasmic space. The Anabaena alr0075, alr2269 and alr4893 gene products were characterized as Omp85-like proteins, which are generally involved in outer membrane protein biogenesis. Open reading frame alr2269 is the first gene of an operon that also carries genes for lipopolysaccharide lipid A biosynthesis including alr2270 (an lpxC homologue). Strains carrying inactivating alr2269 or alr2270 constructs showed enhanced sensitivity to erythromycin, SDS, lysozyme and proteinase K suggesting that they produce an outer membrane with increased permeability. These strains further exhibited increased uptake of sucrose, glutamate and, to a lesser extent, a few other amino acids. Increased uptake of the same metabolites was obtained by mechanical fragmentation of wild-type Anabaena filaments. These results document that the outer membrane is a permeability barrier for metabolites such as sucrose and glutamate, which are subjected to intercellular exchange in the diazotrophic filament of heterocyst-forming cyanobacteria.

Structure and Conservation of the Periplasmic Targeting Factor Tic22 Protein from Plants and Cyanobacteria

“…Generation, Growth, and handling of Anabaena StrainsPlasmids (Table 1) or Anabaena strains (Table 2) were described or generated as established (22)(23)(24). For cloning of alr0114 (anatic22), PCR was performed on genomic DNA of Anabaena sp.…”

The TolC-like Protein HgdD of the Cyanobacterium Anabaena sp. PCC 7120 Is Involved in Secondary Metabolite Export and Antibiotic Resistance

“…Furthermore, the mutants of the other two Omp85-like genes (alr0075 and alr4893) (54,57,58) do not show an overlapping phenotype with the hgdD mutant (59) with respect to heterocyst development (5) or the sensitivity of AFS-I-hgdD to 30 mM lysozyme (59). A function of Alr0075 in HgdD insertion and assembly is further unlikely because this Omp85-like protein only exists in vegetative cells (54), whereas the expression of hgdD is enhanced in heterocysts (5). This could suggest that in Anabaena sp., the function of the Omp85 is not required for the assembly of HgdD, which, however, has to be further investigated.…”

“…Additionally, we used AFS-I-anaOmp85, in which the outer membrane protein assembly was most likely affected (53,54). However, it has to be mentioned that this mutant is not fully segregated, although a drastic phenotype can be observed (54).…”

Relative Orientation of POTRA Domains from Cyanobacterial Omp85 Studied by Pulsed EPR Spectroscopy

“…Although Anabaena sp. contains three open reading frames coding for distinct Omp85 proteins (17), the one encoded by alr2269 (hereafter referred to as anaOmp85) is considered the most abundant Omp85 protein in the outer membrane (18) and is the subject of this study. anaOmp85 contains three POTRA domains (anaP1, anaP2, and anaP3), which were found to regulate the pore gating of the b-barrel (5,15,19).…”