S-layers on cell walls of cyanobacteria

The genome of S-PM2, a "photosynthetic" T4-type bacteriophage that infects marine Synechococcus strains

Bacteriophage S-PM2 infects several strains of the abundant and ecologically important marine cyanobacterium Synechococcus. A large lytic phage with an isometric icosahedral head, S-PM2 has a contractile tail and by this criterion is classified as a myovirus (1). The linear, circularly permuted, 196,280-bp double-stranded DNA genome of S-PM2 contains 37.8% G+C residues. It encodes 239 open reading frames (ORFs) and 25 tRNAs. Of these ORFs, 19 appear to encode proteins associated with the cell envelope, including a putative S-layer-associated protein. Twenty additional S-PM2 ORFs have homologues in the genomes of their cyanobacterial hosts. There is a group I self-splicing intron within the gene encoding the D1 protein. A total of 40 ORFs, organized into discrete clusters, encode homologues of T4 proteins involved in virion morphogenesis, nucleotide metabolism, gene regulation, and DNA replication and repair. The S-PM2 genome encodes a few surprisingly large (e.g., 3,779 amino acids) ORFs of unknown function. Our analysis of the S-PM2 genome suggests that many of the unknown S-PM2 functions may be involved in the adaptation of the metabolism of the host cell to the requirements of phage infection. This hypothesis originates from the identification of multiple phage-mediated modifications of the host's photosynthetic apparatus that appear to be essential for maintaining energy production during the lytic cycle.

Classification of hyper-variable Corynebacterium glutamicum surface-layer proteins by sequence analyses and atomic force microscopy

The structural S-layer proteins of 28 different Corynebacterium glutamicum isolates have been analyzed systematically. Treatment of whole C. glutamicum cells with detergents resulted in the isolation of S-layer proteins with different apparent molecular masses, ranging in size from 55 to 66 kDa. The S-layer genes analyzed were characterized by coding regions ranging from 1,473 to 1,533 nucleotides coding for S-layer proteins with a size of 490-510 amino acids. Using PCR techniques, the corresponding S-layer genes of the 28 C. glutamicum isolates were all cloned and sequenced. The deduced amino acid sequences of the S-layer proteins showed identities between 69 and 98% and could be grouped into five phylogenetic classes. Furthermore, sequence analyses indicated that the S-layer proteins of the analyzed C. glutamicum isolates exhibit a mosaic structure of highly conserved and highly variable regions. Several conserved regions were assumed to play a key role in the formation of the C. glutamicum S-layers. Especially the N-terminal signal peptides and the C-terminal anchor sequences of the S-layer proteins showed a nearly perfect amino acid sequence conservation. Analyses by atomic force microscopy revealed a committed hexagonal structure. Morphological diversity of the C. glutamicum S-layers was observed in a class-specific unit cell dimension (ranging from 15.2 to 17.4 nm), which correlates with the sequence similarity-based classification. It could be demonstrated that differences in the primary structure of the S-layer proteins were reflected by the S-layer morphology.

Inactivation of swmA results in the loss of an outer cell layer in a swimming synechococcus strain

The mechanism of nonflagellar swimming of marine unicellular cyanobacteria remains poorly understood. SwmA is an abundant cell surface-associated 130-kDa glycoprotein that is required for the generation of thrust in Synechococcus sp. strain WH8102. Ultrastructural comparisons of wild-type cells to a mutant strain in which the gene encoding SwmA has been insertionally inactivated reveal that the mutant lacks a layer external to the outer membrane. Cryofixation and freeze-substitution are required for the preservation of this external layer. Freeze fracturing and etching reveal that this additional layer is an S-layer. How the S-layer might function in motility remains elusive; however, this work describes an ultrastructural component required for this unique type of swimming. In addition, the work presented here describes the envelope structure of a model swimming cyanobacterium.