The life cycles of two species of Myxomycetes in Physarales, Physarum rigidum and Didymium squamulosum.

Myxomycetes are eukaryotic microorganisms containing characteristics akin to both fungi and amoebae. They can complete their whole life cycles while being cultured on agar media, and under-laboratory conditions, which favors taxonomic, phylogenetic, and cytological researches. Here, we describe the life cycles of two such species: Didymium squamulosum collected from the field and Physarum rigidum cultured from moist chamber both belonging to the Order Physarales. Three per cent oat-agar media (OAM) was used to culture the plasmodia until they aggregated and were almost starved. Natural light was then applied to the plasmodia to induce fructification. Their life cycles share the same common stages, namely: spore, myxamoebae, swarm cell, plasmodia, and sporulation. In this study, we describe the morphogenesis from spore to spore of two species by differential interference contrast (DIC) and stereoscopic microscopies, as well as discuss the differences between the development of both species and interspecies. We found that the spore germination method of both species was the same. However, there were differences noted in time taken and fruiting body formation. Unlike P. rigidum, the species D. squamulosum did not require natural light stimulation. Moreover, the maturation process of both species had similar color transitions but exhibited distinct morphology in each developmental stage except during the swarm cell stage.

Mycetozoal bloom in a hydroponic culture of garden cress (Lepidium sativum L.).

The role and importance of the true slime moulds (mycetozoans, Mycetozoa, formerly Myxomycetes) for agriculture and food industry are poorly documented, most probably because of a low popularity of these "macroscopic microorganisms" among researchers in the past. Here we report probably for the first time the massive occurrence of true slime moulds in their vegetative, plasmodial form in a product intended for direct consumption, i.e. in a household hydroponic culture of garden cress (Lepidium sativum L.). The plasmodia gradually produced numerous, stalked or sessile sporangia and plasmodiocarps, which made it possible to identify them as Didymium species complex (the stalked sporangia) and Didymium difforme (Pers.) Gray (the sessile sporangia and plasmodiocarps). The mycetozoans were transferred to in vitro culture where they were maintained for several weeks on oat flour. We briefly discuss the importance of this observation from the point of view of biochemical interactions between the plant and the true slime moulds in a general context of slime mould biology. Our observation indicates that the presence of mycetozoan material in food products may be frequent, while its influence on food safety and quality remains unknown.

Description and culture of a new succulenticolous Didymium (Myxomycetes).

A new succulenticolous Myxomycete species, Didymium wildpretii, found on decaying remains of various species of cacti, is described from two arid zones of the world. This species was collected from central Mexico, at the southern limit of the Chihuahuan Desert, and from the Canary Islands (Spain). The new species has small, pale yellow sporocarps, 0.1-0.7 mm high, that are sessile or have short, orange-yellow, calcareous stalks and small, uniformly warted spores. The stability of the taxonomic characters of the species was confirmed with both moist chamber cultures and spore-to-spore culture on agar. Life cycle events are described from germination to sporulation. Myxomycete specimens were examined with scanning electron microscopy and light microscopy, and micrographs of relevant morphological details are included.

Mitochondrial inheritance patterns in Didymium iridis are not influenced by stage of mating competency.

To test whether the timing of transition to mating competency affected mitochondrial transmission patterns in D. iridis. Reciprocal crosses were made by combining mating compatible strains that differed in their competency to mate. The results were compared to crosses where both mating strains were competent at the time of combining and crosses where somatic fusion of plasmodia was allowed. The results show that the mating competency of the parental strains at the time of confronting a compatible mate does not affect mitochondrial transmission patterns, mating efficiency or the likelihood of biparental inheritance. However the timing of plasmodial formation is delayed when precompetent and competent strains are mated compared to when both strains are competent at the time of mixing. We also observed that somatic fusion of plasmodia did not appreciably increase the incidence of biparental inheritance compared to crosses where individual plasmodia were isolated. These results provide additional evidence of the variable nature of mitochondrial inheritance in D. iridis within crosses and between mating trials.