GROWTH AND DEVELOPMENT OF THE MYXOMYCETE PERICHAENA VERMICULARIS. I. CULTIVATION AND VEGETATIVE NUCLEAR DIVISIONS

The isolation and successful two-membered culture of the homothallic myxomycete Perichaena vermicularis (order Trichiales) is reported for the first time. Comparisons of mitosis in amoebae, zygotes and plasmodia as seen with phase contrast microscopy are made anid distinguishirng features of the different kinds of nuclear behavior are discussed. IN RECENT YEARS several investigators have made use of plasmodial slime molds in developmental, physiological, cytological, and genetical studies (Guttes, Guttes, and Rusch, 1961; Alexopoulos, 1963; Collins,1963; Ross and Sunshine, 1965; Aldrich, 1967). Much of the work has been done on the same few species, such as Physarum polycephalum, other species of Physarum, and various Didymium species, mainly because these species are among the few that have .been successfully cultured in the laboratory. The reports of Alexopoulos (1960), Wollman and Alexopoulos (1964), and McManus (1961, 1962) of the cultivation of various slime molds belonging to different orders indicate that other Myxomycetes may be cultured under the appropriate conditions. In many cases, however, laboratory cultures of such species have been reported to die out or be very difficult to maintain. Furthermore, it has become evident from the investigations mentioned above that Myxomycetes are quite variable not only among species and genera, but also among different isolates of the same species and among clonal cultures grown under different conditions. It is important, therefore, not only to continue to isolate and attempt to cultivate other species, but also to follow such species throughout their life cycles so that patterns of variability may eventually be established. Lacking such a foundation experimental results may be liable to misinterpretation, and apparent conflicting evidence may lead to unnecessary controversy. The isolation and successful cultivation through many generatio'ns of Perichaena vermiculdtris (order Trichiales) in the laboratory, together with details of the nuclear behavior in the vegetative stages of the life cycle, are therefore presented. Details of the nuclear cycle and 1 Received for publication July 20, 1966. Supported by grant GB-4396 from the National Science Foundation. The technical assistance of Mrs. Frances Shrader is gratefully acknowledged. of sporulation will be reported in a subsequent paper. 1MJATERIALS AND METHODs-Plasmodiocarps of Perichaena vermicularis (Schw.) Rost. were found in moist chambers of unidentified tree bark sent to me from AMiami, Fla. Spores from these plasmodiocarps were sown oni BBIJ corn meal agar and flooded with water. Subsequent cultures from plasmodiocarps which formed oni the corn meal agar were made on a steer dung-oatmeal extract agar (DOA) with Escher-ichia coli as food. The plates were kept very moist with a distinct film of water covering the agar. Amoebal populations were larger, plasmodia more vigorous and sporulation more uniform on the DOA than -on the corn meal agar. Observations on amoebae and small plasmodia were made in polyethylene ring microcultures described previously (Ross, 1967). Chromosome counts were made from amoebae killed in 65%o acetic acid and heat-dried on slides before mounting in aceto-orcein (Ross, in press). Photographs were made through a Zeiss WL microscope equipped with phase contrast optics on Kodak High Contrast Copy film using a Leitz Mikroblitz electronic flash as illumination. OBSERVATIONS AND DISCUSSION-Spore to spore cultivation-On DOA the life cycle of P. vermicularis from spore to spore is completed in 5-7 days. Spore germination begins 40-70 min after the spores have been sown on flooded agar, microscopic plasmodia (i.e., Fig. 20) are visible after 24 hr and macroscopic plasmodia (Fig. 2) are evident in 48-72 hr. Sporulation occurs 3-4 days after the large plasmodia have formed. This cycle has been maintained through 15 generations under the normal fluctuations of laboratory light and temperature (19-22 C) without gross variation. Spores have remained viable for at least 3 months, with germination ranging from 70-95%, the higher percentages being