Symposium on bacterial spores: 8. The diversity of bacterial spores

Development and evaluation of a method for the quantification of airborne Thermoactinomyces vulgaris by real-time PCR

Actinomycetes are ubiquitous and some can be potentially pathogenic for humans when present in the air of some working areas. It's notably the case for Thermoactinomyces vulgaris in composting facilities where aerial concentrations can reach high values of more than 10(7) CFU·m(-3). Workers exposure to these inhalable bioaerosols can be the source of various diseases. The literature reveals a lack of knowledge about risk assessment: there is neither dose-effects relationship for most agents, or threshold limit value. The objectives of this study were to develop and standardize a method to quantify workers exposure to bioaerosols. We have developed and evaluated a method to quantify airborne T. vulgaris based on DNA extraction of aerial microbial communities and qPCR. Four DNA extraction protocols were compared, and primers and a hydrolysis probe were designed for specific amplification of the target species (gyrB gene). This method was compared to traditional methods based on viable or cultivable counting by epifluorescence microscopy or plating on selective media. The method was applied on environmental bioaerosols sampled under real exposure conditions in composting plants. We demonstrate that the method to quantify T. vulgaris in bioaerosols is specific, sensitive and repeatable. We demonstrate the occurrence and quantified T. vulgaris in the atmosphere of composting facilities with concentrations ranging from 3×10(2) to 3×10(6)×m(-3).

Application of sucrose-gradient centrifugation for selective isolation of Nocardia spp. from soil

AIMS

To devise and evaluate a method for selective isolation of the less abundant actinomycetes, Nocardia spp. in soil.

METHODS AND RESULTS

This newly developed method is based on differentiating Nocardia from other actinomycete taxa by centrifugation. A water suspension of air-dried soil is centrifuged through a gradient consisting of 10, 20, 30, 40 and 50% sucrose at 240 x g for 30 min. The 20% sucrose layer, which is enriched with Nocardia spp., is then diluted and plated on humic acid-vitamin agar supplemented with antibacterial agents. The proposed method consistently achieved selective isolation of Nocardia spp. in all 14 soil samples tested, which accounted for 5-89% of the total microbial population recovered. Tentative taxonomic characterization based on a restriction fragment length polymorphism (RFLP) analysis of the 16S ribosomal DNA suggested that many of the soil isolates could belong to N. asteroides, N. salmonicida or N. uniformis.

CONCLUSIONS

Differential centrifugation can successfully and efficiently isolate soil Nocardia populations that are suppressed by conventional dilution plating approaches.

SIGNIFICANCE AND IMPACT OF THE STUDY

The development and application of new methodologies with which to isolate less-explored actinomycete taxa is important for improving our knowledge about their taxonomy, ecology and industrial applications.

Bacterial parasite of a plant nematode: morphology and ultrastructure

The life cycle of a bacterial endoparasite of the plant-parasitic nematode Meloidogyne incognita was examined by scanning and transmission electron microscopy. The infective stage begins with the attachment of an endospore to the surface of the nematode. A germ tube then penetrates the cuticle, and mycelil colonies form in the pseudocoelom. Sporulation is initiated when terminal cells of the mycelium enlarge to form sporangia. A septum within each sporangium divides the forespore from the basal or parasporal portion of the cell. The forespore becomes enclosed by several laminar coats. The parasporal cell remains attached to the forespore and forms the parasporal microfibers. After the newly formed spores are released into the soil, these microfibers apparently enable a mature spore to attach to the nematode. These results indicate that the endoparasite is a procaryotic organism having structural features that are more common to members of Actinomycetales and to the bacterium Pasteuria ramosa than to the sporozoans or to the family Bacillaceae, as previous investigatios have concluded.

Ultrastructural studies of sporulation in Streptomyces

This is the first study of sporogenesis in Streptomyces carried out on a relatively high number of species (seven) which allows us, using also previously published results, to establish a general picture of this process. In the sporogenesis of Streptomyces two basic stages can be considered: the sporulation septum synthesis and the arthrospore maturation. Our ultrastructural study of the sporulation septum formation suggests the existance within this genus of three basic types. Type I is distinguished because the septum is formed from the beginning by two separate cross walls. Within this type we include Streptomyces erythraeus, Streptomyces albus, and Streptomyces aureofaciens and also include Streptomyces venezuelae, Streptomyces griseus, and Streptomyces osteogriseus. Type II is distinguished because there is a deposit of material previous to the synthesis of the double annulus which completes the septum. This type can be divided into two subtypes. In the first the deposits are wedge-shaped and the double annulus is clearly visible, and to this group belong Streptomyces flaveolus, Streptomyces ambofaciens, and Streptomyces coelicolor. In the second the deposits, which have a different shape and are very well developed, constitute almost entirely the sporulation septum in which the double annulus is barely visible; Streptomyces antibioticus and also Streptomyces viridochromogenes belong to this group. Type III, represented by Streptomyces cinnamonensis, is distinguished because the septum is formed by a single cross wall.