Zygospore

Abstract: The Rhizopus oryzae species complex is a group of zygomycete fungi that are common, cosmopolitan saprotrophs. Some strains are used beneficially for production of Asian fermented foods but they can also act as opportunistic human pathogens. Although R. oryzae reportedly has a heterothallic (+/2) mating system, most strains have not been observed to undergo sexual reproduction and the genetic structure of its mating locus has not been characterized. Here we report on the mating behavior and genetic structure of the mating locus for 54 isolates of the R. oryzae complex. All 54 strains have a mating locus similar in overall organization to Phycomyces blakesleeanus and Mucor circinelloides (Mucoromycotina, Zygomycota). In all of these fungi, the minus (2) allele features the SexM high mobility group (HMG) gene flanked by an RNA helicase gene and a TP transporter gene (TPT). Within the R. oryzae complex, the plus (+) mating allele includes an inserted region that codes for a BTB/POZ domain gene and the SexP HMG gene. Phylogenetic analyses of multiple genes, including the mating loci (HMG, TPT, RNA helicase), ITS1-5.8S-ITS2 rDNA, RPB2, and LDH genes, identified two distinct groups of strains. These correspond to previously described sibling species R. oryzae sensu stricto and R. delemar. Within each species, discordant gene phylogenies among multiple loci suggest an outcrossing population structure. The hypothesis of random-mating is also supported by a 50:50 ratio of plus and minus mating types in both cryptic species. When crossed with tester strains of the opposite mating type, most isolates of R. delemar failed to produce zygospores, while isolates of R. oryzae produced sterile zygospores. In spite of the reluctance of most strains to mate in vitro, the conserved sex locus structure and evidence for outcrossing suggest that a normal sexual cycle occurs in both species.

Abstract: This review surveys on the influence of different environmental factors like light (intensity, quality, photoperiod), temperature, season, nutrients (inorganic, organic), biotic factors (algal extracellular products, bacterial association, animals grazing), osmotic stress, pH of the medium, wave motion and mechanical shock, pollution, and radiations (UV, X-rays, gamma radiation) on the induction (or inhibition) of algal reproduction like cell division in unicellular algae, and formation of zoospores, aplanospores, akinetes, cysts, antheridia, oogonia, zygospores, etc.

Abstract: Certain species of the Mucorineae, or black mold group of fungi, are composed of two distinct strains, either of which is capable of living by itself and of producing asexual spores, but neither is able alone to produce the zygospores or sexual stage. When the two strains are together, however, and the environment is suitable, the sexual spores are produced abundantly. In the formation of the zygospores, one gamete is produced by one strain and the other gamete by the other strain. In this group of fungi, the strains are very similar; in most cases it being impossible to differentiate between them from a macroscopic or microscopic examination. While these two are without doubt sexual strains, their similarity has made it seem advisable to Blakeslee, who has made a study of many of the forms, to use the indefinite terms, plus and minus, in preference to male and female Outside of the Mucorineae sexual strains in fungi are either very rare or else have not been recognized and it would seem that they are very rare as many unsuccessful attempts have been made to find them. However in the genus Glomerella, which is the perithecial stage of certain species in the form genera, Gloeosporium and Colletotrichum, a condition exists which approaches that found in the Mucorineae. The ascogenous stages of many of the Gloeosporiums and Colletotrichums have been known for a number of years. In some of the forms, as for example the one causing the bitter rot disease of apples, the perithecial stage is rather'common, while in others its development seems to be rare. Yet with all of the forms the perithecia develop very erratically sometimes present in abundance and other times entirely absent. While working on these fungi during the past several years and trying to find out some of the reasons of the erratic development of the perithecia, the writer has constantly had in mind the possibility of sexual strains. Until about three or four years ago, nothing developed which would in the least show that more than one 244

Abstract: The information available regarding the survival of freshwater algae during dry periods is somewhat meagre. Text-books (Fritsch 1935; Smith 1938, 1951; West & Fritsch 1927) refer to 'resting cells', 'cysts', 'akinetes' and 'resistant stages' but with some exceptions little appears to be known in detail about the droughtsurvival value of these stages. Physiologically, a cell or a group of cells in which growth has ceased, temporarily at least, and in which the metabolic processes are at a minimum may be said to be a resting stage. This is a wide definition and includes such structures as resting oospores, zygospores, hypnospores and akinetes. For each algal species one or more of these stages might assist in the survival of the species during dry conditions. Str0m (1924), referring to the overwintering of algae, said that the importance of zygospores and other resting spores had been greatly exaggerated and also pointed out that it is incorrect to generalize, as species of a genus may differ widely in their reactions to any particular condition. Bristol (1920) found that algae surviving in old stored soils (26-73 years old) included members of the Cyanophyceae, the Chlorophyceae and one diatom, Nitzschia palea. Certain terrestrial algae have been investigated with regard to the survival of vegetative stages during drought by Fritsch (1922) and Fritsch & Haines (1923). Various references have been made to the accumulation of granular bodies or oil globules in organisms exposed to periods of desiccation (Denffer 1949; Fritsch 1916, 1944; Heide 1939; Kahn 1949; Petersen 1935; Piercy 1917; Salah 1952). Rao (1953) carried out some work on the algae of a pond which eventually dried up but he found no resting stages. Lund (1942) observed an immediate decrease in the algal flora of exposed pond-bottom deposits when the surface of the mud areas began to dry, but found no stages of the normally aquatic algae which he could