Why are rod-shaped bacteria rod shaped?

Generally speaking, bacteria grow and divide indefinitely, and as long as the growth conditions are maintained they retain constant dimensions and shapes with little variation. How they do this is a question that I have been considering for three decades. Here, I discuss two hypothetical mechanisms, one for Gram-positive rods and the other for Gram-negative rods. These mechanisms are consistent with what is known, but make some unproven assumptions.

[Electron microscope investigation of bacteria associated with the tegument of the tapeworm species Eubothrium rugosum, a parasite of the intestine of burbot].

Bacteria associated with the tegument of the tapeworm species Eubothrium rugosum (Cestoda, Pseudophyllidea) parasitizing the intestine of burbot (Lota lota) were studied using transmission and scanning electron microscopy. Three morphological types of the bacteria were revealed. Bacteria of the first type are localized between microtrichia and fit to them closely. Bacteria of the second (gram-positive) and third (gram-negative) types are localized over microtrichia of the tegument and do not attach to the surface. Physiological functions of the bacteria are discussed.

Structure of the Na+-driven flagellum from the homoacetogenic bacterium Acetobacterium woodii.

The Na+-dependent flagellum of Acetobacterium woodii was characterised. Flagellin and whole flagella were purified and analysed by SDS-PAGE and electron microscopy. The structure and dimensions of the filament and the hook-basal body, as revealed by electron microscopy, resemble those of H+-dependent flagella from gram-positive bacteria. Intramembrane particle rings were present at the cell pole in freeze-fractured A. woodii cells, which might correspond to the mot complex.

Ultrastructural analysis of an infected collagen-coated vascular graft.

The incidence of infection following arterial reconstruction using synthetic graft materials varies from less than 1 to 5%. One of three mechanisms is thought to be responsible: 1. intraoperative contamination, 2. extension from adjacent infected or colonized tissue, or 3. hematogenous or lymphogenous seeding. We present ultrastructural data of a patient with a polymicrobial graft infection due to a prostheto-enteric fistula 16 years after reconstruction of an aortobifemoral graft. The polymer surface showed signs of biodegradation and was completely covered with a layer of plasma proteins. Disrupted fibroblasts on the intersegmental graft surface were surrounded by bundles of collagen. Gram-negative rods and grampositive cocci were embedded in an extracellular EPS matrix. Bacterial culture confirmed growth of Eikenella corrodens, Fusobacterium nucleatum and Peptostreptococcus species. Fibrin and granulation tissue from the neoadventitia started to mark off the inflammatory process. Transmission electron microscopy is a valuable tool for the investigation of alloplastic arterial devices. After 16 years of implantation the graft shows different signs of biodegradation.

Catarrhal proventriculitis associated with a filamentous organism in pet birds.

Catarrhal proventriculitis due to infection by an unidentified organism was diagnosed in 79 of 534 pet birds examined histologically. It was more prevalent in domestic birds (70 cases) than in imported ones (9 cases). A high incidence of the disease was encountered in budgerigars (Melopsittacus undulatus) and it was occasionally found in finches (Poephila gouldiae gouldiae), parakeets (Psittacula Krameri manillensis), Amazona parrots (Amazona aestiva aestiva) and cockatiels (Nymphicus hollandicus). The agent was a large filamentous rod, and was stained positively with Gram, GMS and PAS methods. Histologically, it induced a mild to moderate exudative or proliferative inflammation in the proventriculus. All the cases had an erosion in the gizzard. Ultrastructurally, the organism had a eukaryotic nucleus and three cell-wall layers. Concurrent infections were very common, including adenoviruses (37 cases), giardiasis (31 cases), candidiasis (13 cases), papovaviruses (11 cases) and knemidocoptic mites (11 cases).

Caldalkalibacillus thermarum gen. nov., sp. nov., a novel alkalithermophilic bacterium from a hot spring in China.

A thermophilic, alkaliphilic and catalase-positive bacterium, designated strain HA6(T), was isolated from a hot spring in China. The strain was aerobic and chemo-organotrophic and grew optimally at 60 degrees C, pH 8.5 and 1.5 % (w/v) NaCl. The cells were Gram-positive rods, forming single terminal endospores. The predominant cellular fatty acids were iso-C(15 : 0) and iso-C(17 : 0). The cell-wall peptidoglycan contained meso-diaminopimelic acid. The genomic DNA G+C content was 45.2 mol%. Phylogenetic analysis based on the 16S rRNA gene sequence revealed that strain HA6(T) formed a distinct lineage within the family Bacillaceae and was most closely related to Bacillus horti K13(T) and Bacillus smithii DSM 4216(T), with sequence similarities of 91.8 and 93.1 %, respectively. On the basis of its physiological and molecular properties, strain HA6(T) should be placed in a novel genus and species, for which the name Caldalkalibacillus thermarum gen. nov., sp. nov. is proposed. The type strain of Caldalkalibacillus thermarum is strain HA6(T) (=CGMCC 1.4242(T)=JCM 13486(T)).

Roseburia intestinalis sp. nov., a novel saccharolytic, butyrate-producing bacterium from human faeces.

Five strains of butyrate-producing, anaerobic, gram-positive bacteria were isolated from human faecal material. These strains were slightly curved rods that showed motility by means of multiple subterminal flagella. The DNA G + C content of the strains was 29-31 mol%. A detailed investigation of the phenotypic and phylogenetic characteristics of the strains revealed that they represent a novel species of anaerobic, low-G+C-content, butyrate-producing bacterium that shows net acetate utilization during growth on media containing carbohydrates and short-chain fatty acids. The 16S rRNA gene sequences of the five isolates were determined and they confirmed that these strains were closely related to each other. Phylogenetic analysis indicated that the most closely related species are Eubacterium rectale, Eubacterium oxidoreducens and Roseburia cecicola, members of cluster XIVa of the Clostridium subphylum of gram-positive bacteria, although they share less than 95% sequence identity with the novel strains. It is proposed that a novel species, Roseburia intestinalis sp. nov., be created, with strain L1-82T (= DSM 14610T = NCIMB 13810T) as the type strain.