Scanning electron microscopy analysis of agedMycobacterium tuberculosiscells

Most electron microscopy studies of Mycobacterium tuberculosis ultrastructure were performed in the 1950s and 1960s and lack high resolution by modern standards. This study was performed to re-evaluate the fine structure of M. tuberculosis using modern scanning electron microscopy. Bacteria were grown in rich medium with a constant supply of oxygen for several weeks. Results show that surface bleb-like structures accumulate as cultures age. The most unusual feature of aging M. tuberculosis cultures is that they develop extracellular fibrils, which could play roles of adhering cells to surfaces and to one another.Key words: Mycobacterium tuberculosis, SEM, stationary phase, surface blebs, extracellular fibrils.

Attachment of Arcobacter butzleri, a New Waterborne Pathogen, to Water Distribution Pipe Surfaces

The capability of Arcobacter butzleri to attach to various water distribution pipe surfaces, such as stainless steel, copper, and plastic, was evaluated using scanning electron microscopy. Our results indicated that Arcobacter cells could easily attach to all surface types and the number of attached cells depended on the length of exposure and temperatures (4 and 20°C). Extracellular fibrils were also observed on the stainless steel surface, especially after 72 h of contact times at both refrigeration and ambient temperatures. In addition, the surface energy value of each material was estimated by contact angle measurements using water, α-bromonaphthalene, and dimethylsulfoxide. The surface energy of A. butzleri was 58.6 mJ·m−2 and the surface energy values of the three surfaces studied showed that plastic had a low energy surface (26.1 mJ·m−2) as did copper (45.8 mJ·m−2) and stainless steel (65.7 mJ·m−2).

Morphogenesis of shell and scutes in the turtle Emydura macquarii

Formation of the scutes and dermis of the embryonic shell of the turtle Emydura macquarii was studied using light and electron microscopy. Shell morphogenesis begins at embryonic stage 15 and the shape of the shell is mostly completed by embryonic stage 19. The carapace anlagen arises as a thickening of the skin in the dorsal part of the mid-trunk region between the anterior and posterior limbs. This thickening extends ventro-laterally to form ridges at the margins of the carapace. Each ridge forms as a thick epidermal placode over a condensation of mesenchymal cells. The epidermis behind the advancing margins of the carapace is cuboidal or columnar but does not form placodes. The margins of the carapace expand rapidly in all directions. The plastron anlagen is derived from epidermal cells localised in the latero-ventral regions between the fore- and hind-limbs. Plastron placodes are present laterally, while the mid-ventral and central epidermis remains cuboidal or columnar but does not form placodes at embryonic stage 16. The plastron thickening rapidly moves from a latero-ventral position to a flat ventral position between embryonic stages 16 and 19. Dermal–epidermal anchoring complexes occur throughout placodes of both the carapace and plastron, but are rare in non-placode areas. The accumulation of a dense mesenchyme beneath the shell epidermis forms a dermal cushion that surrounds the body cavity. The superficial dermis close to the epidermis is made of mesenchymal fibroblasts at embryonic stage 19, although the inner-most areas contain bipolar fibroblasts and extracellular fibrils. Scutes with serrations at their borders form as invaginations of the epidermis into the dermis in the mid-dorsal areas of the embryo at embryonic stages 18–19. Dermal–epidermal anchoring complexes are located around the infoldings that form the scutes of the hinge region. The epidermis of the shell has 2–3 suprabasal cells at embryonic stages 19–22, and lacks keratinisation before embryonic stage 22 when it has 4–6 suprabasal layers with 2–3 external layers made of flat cells. The dermis thickens and has numerous collagen fibrils after embryonic stage 19. The formation of dermal bones begins at embryonic stage 18–19 in the plastron. Only small areas of the carapace near to the bridge have begun to form dermal bone at embryonic stage 19. Calcification begins at embryonic stage 19, but is still incomplete at embryonic stages 24–25.

A Chaperone in the HSP70 Family Controls Production of Extracellular Fibrils in Myxococcus xanthus

ABSTRACT Three independent Tn5-lac insertions in the S1 locus ofMyxococcus xanthus inactivate the sglK gene, which is nonessential for growth but required for social motility and multicellular development. The sequence of sglK reveals that it encodes a homologue of the chaperone HSP70 (DnaK). ThesglK gene is cotranscribed with the upstreamgrpS gene, which encodes a GrpE homologue. UnlikesglK, grpS is not required for social motility or development. Wild-type M. xanthus is encased in extracellular polysaccharide filaments associated with the multimeric fibrillin protein. Mutations in sglK inhibit cell cohesion, the binding of Congo red, and the synthesis or secretion of fibrillin, indicating that sglK mutants do not make fibrils. ThefibR gene, located immediately upstream of thegrpS-sglK operon, encodes a product which is predicted to have a sequence similar to those of the repressors of alginate biosynthesis in Pseudomonas aeruginosa andPseudomonas putida. Inactivation of fibR leads to the overproduction of fibrillin, suggesting that M. xanthus fibril production and Pseudomonas alginate production are regulated in analogous ways. M. xanthus andPseudomonas exopolysaccharides may play similar roles in a mechanism of social motility conserved in these gram-negative bacteria.