Zoospores of Undaria pinnatifida: their efficiency to attach under different water velocities and conjugation behavior during attachment

In the invading course of Undaria pinnatifida, zoospore attachment in a dynamically changed subtidal water environment is crucial for the establishment of a potential population in alien waters. Among many abiotic factors that may interfere with the attachment process, water velocity is the most important one. In this investigation, the effect of water velocity on zoospore attachment of U. pinnatifida was investigated in an artificially designed system. It was found that freshly released zoospores that were transported by water flowing at 0 similar to 16 cm/s showed no difficulty in attaching the smooth surface. Zoospore attachment decreased at elevated water flowing rates. At 70 cm/s no spore attachment occurred. Spores that have settled on glass slide for up to I h could not be stripped away by flowing water at a rate of 129 cm/s, the same was true of the 20 d old filamentous gametophytes. It was found that more than 70% of free-swimming zoospores tended to settle down adjacent to the settled spores and formed conjugated clusters from two up to a few hundred cells in still culture.

Use of a New Tetrazolium-Based Assay to Study the Production of Superoxide Radicals by Tobacco Cell Cultures Challenged with Avirulent Zoospores of Phytophthora parasitica var nicotianae1

The relationship between the production of reactive oxygen species and the hypersensitive response (HR) of tobacco (Nicotiana tabacum L.) toward an incompatible race of the Oomycete Phytophthora parasitica var nicotianae has been investigated. A new assay for superoxide radical (O2−) production based on reduction of the tetrazolium dye sodium,3′-(1-[phenylamino-carbonyl]-3,4-tetrazolium)-bis(4-methoxy-6-nitro) benzene-sulfonic acid hydrate (XTT) has enabled the quantitative estimation of perhydroxyl/superoxide radical acid-base pair (HO2·/O2−) production during the resistant response. Tobacco suspension cells were inoculated with zoospores from compatible or incompatible races of the pathogen. Subsequent HO2·/O2− production was monitored by following the formation of XTT formazan. In the incompatible interaction only, HO2·/O2− was produced in a minor burst between 0 and 2 h and then in a major burst between 8 and 10 h postinoculation. During this second burst, rates of XTT reduction equivalent to a radical flux of 9.9 × 10−15 mol min−1 cell−1 were observed. The HO2·/O2− scavengers O2− dismutase and Mn(III)desferal each inhibited dye reduction. An HR was observed in challenged, resistant cells immediately following the second burst of radical production. Both scavengers inhibited the HR when added prior to the occurrence of either radical burst, indicating that O2− production is a necessary precursor to the HR.

Influence of environmental factors on zoospores of Saprolegnia diclina

The numbers of zoospores produced by a pathogenic strain of Saprolegnia diclina and their behaviour are markedly influenced by a variety of environmental variables including temperature, pH, oxygen tension and the presence of biocides. The use of the latter is not recommended, as fish readily succumb to equivalent concentrations of biocides. Analysis of the pattern of distribution of resulting zoospore cysts demonstrates that zoospores become dispersed by random movement even while in the proximity of the parent colony’s nutrient source. However, the presence of amino acids, in particular aspartic and glutamic acid, at concentrations which occur in fish tissue promotes the directed movement of zoospores towards the nutrient source thereby encouraging the colonization of fresh sites.

Mobilization of Pollutant-Degrading Bacteria by Eukaryotic Zoospores

Peer reviewed

Screening bacterial metabolites for inhibitory effects against Batrachochytrium dendrobatidis using a spectrophotometric assay

Certain bacteria present on frog skin can prevent infection by the pathogenic fungus Batrachochytrium dendrobatidis (Bd), conferring disease resistance. Previous studies have used agar-based in vitro challenge assays to screen bacteria for Bd-inhibitory activity and to identify candidates for bacterial supplementation trials. However, agar-based assays can be difficult to set up and to replicate reliably. To overcome these difficulties, we developed a semi-quantitative spectrophotometric challenge assay technique. Cell-free supernatants were prepared from filtered bacterial cultures and added to 96-well plates in replicated wells containing Bd zoospores suspended in tryptone-gelatin hydrolysate-lactose (TGhL) broth medium. Plates were then read daily on a spectrophotometer until positive controls reached maximum growth in order to determine growth curves for Bd. We tested the technique by screening skin bacteria from the Australian green-eyed tree frog Litoria serrata. Of bacteria tested, 31% showed some degree of Bd inhibition, while some may have promoted Bd growth, a previously unknown effect. Our cell-free supernatant challenge assay technique is an effective in vitro method for screening bacterial isolates for strong Bd-inhibitory activity. It contributes to the expanding field of bioaugmentation research, which could play a significant role in mitigating the effects of chytridiomycosis on amphibians around the world.

On new or insufficiently-known Chytridinae [Translation from: Archiv fur Protistenkunde 54 168-173 + pl.9, 1926]

This partial translation of a larger paper provides taxonomic descriptions of 5 fungal zoospores species: Olpidium vampyrellae, 0. pseudosporearum, 0. leptophrydis, Rhizophidium leptophrydis and Chytridium lateoperculatum.

In-vitro effect of fungicides on hyphal growth and sporogenesis of Lagenidium sp. isolated from Penaeus monodon larvae and Scylla serrata eggs

The sensitivity of Lagenidium, isolated from Penaeus monodon, Scylla serrata , to 34 antimycotics was determined. Effects on the development of vesicles, zoospores and mycelial growth were evaluated. Although mycoidal levels of the chemicals tested will be ideal for lethal treatment on control of the fungus, the high dose required may be lethal to the host, thus the use of mycostatic concentrations is more practical. Treatments of rearing water containing larvae, adult shrimps or crabs should be done only after preliminary tolerance experiments using at least the mycostatic dose prove to be safe for the hosts. Mycocidal doses can be used for determining disinfection doses of equipment and facilities used in rearing procedures as well as for destroying batches of infected larvae.

Breaking seasonal limitation: year-round sporogenesis in the brown alga Laminaria saccharina by blocking the transport of putative sporulation inhibitors

Year-round induction of sporogenesis of Laminaria saccharina was performed by mechanically blocking the transport of the putative sporulation inhibitors produced by the blade meristem and culturing the plants in constant short days. Sporogenesis was successfully induced by removal of the blade meristem, either by cultivating distal blade fragments or by performing a transverse cut in the frond. The earliest sorus formation after artificial induction was 10 days. The age of the sporophytes used for induction was 6-11 months or 2 years in tank-grown or field-collected sporophytes, respectively. Zoospores were successfully released in all cases. Thus, by year-round artificial induction of sporogenesis, (1) sporeling production of L. saccharina and thereafter sporophyte cultivation could be achieved without seasonal limitation, and (2) the life cycle of L. saccharina (from spore to spore) could be completed within 8 months under controlled conditions. (C) 2004 Elsevier B.V. All rights reserved.

A new method of Laminaria japonica strain selection and sporeling raising by the use of gametophyte clones

One-celled female and male gametophytes of three Laminaria japonica strains were isolated, cultured and gametophyte clones were formed. A technique combining strain selection with sporeling raising by the use of these female and male gametophyte clones was studied. Experiments on 9 different crossing combinations was conducted in November of 1997 in Qingdao, P. R. China. The main economic characteristics, frond length and fresh weight, of sporophytes of different crossing combinations were measured. F-1 sporophytes of No. 2 showed a higher fresh weight and longer length, therefore, No. 2 (Wh860 + x Lid) was selected as a good combination. Its parental female and male gametophyte clones are being mass cultured for sporeling production. By this method, the time needed for strain selection was shortened from 5-6 to 2 years. As compared with the routine method of sporeling raising by the collection of zoospores, the time of sporeling raising of this method decrease by 50%, and the production cost is also reduced by 50%. It is believed that this method will be labour and time saving and a more economic way for strain selection and sporeling raising in L. japonica cultivation industry.

Early development of Costaria costata (C. Agardh) Saunders and cultivation trials

Costaria costata (C. Agardh) Saunders is one of common kelps distributed in many coastal areas worldwide; however, in China, no reports have been made on cultivation of the genus. To investigate potential cultivation of the species in the northern part of China, trials on isolation and preservation of the gametophytes were conducted using C. costata from Korea; growth and development of the gametophytes were observed. We showed that at 10 +/- 1A degrees C, 60 mu mol m(-2)s(-1) and 12:12 h (L:D), freshly released zoospores settled down within 1 hour, and then developed into the primary cell during the following 2 days. After a vegetative growth phase lasting 6-8 days, female gametophytes became 3-4 times larger in diameter than that of the primary cell, but still remained at a unicellular stage, while male gametophytes divided into 4-10 cells with only a slight change in size. Fertilization occurred within 10 days after the zoospores were released from the sporangia, and the apical and basal tissues of the juvenile sporophyte divided and differentiated into the blade and stipe. Temperature and irradiance influenced gametophytic vegetative growth and developmental patterns. Generally, low irradiance (15 mu mol m(-2)s(-1) and 30 mu mol m(-2)s(-1)) was unfavorable to the induction of fertility, but it enhanced female gametophyte division. The optimal conditions for vegetative growth were 15A degrees C and 30 mu mol m(-2)s(-1). After transplantation of the juvenile seedlings and after eight months cultivation, the harvested mature blade reached 194 cm in length and 32.7 cm in width. Our study proves that it is feasible to implement propagation and large scale cultivation of C. costata in northern China.