Achlya bisexualis (Achlyaceae, Saprolegniales, Oomycota) – A new record for India

In the present report, Achlya bisexualis Coker and Couch is isolated, described and illustrated based on morpho-physiological characteristics and molecular analysis. The oogonial thallus of this dioecious (heterothallic) species is mainly recognized by the presence of predominantly spherical or pyriform gemmae and spherical or obpyriform oogonia with non-maturing oospores. The isolated specimen was identified by sequences comparison of the D1/D2 domains of the LSU and ITS-rDNA. To the best of our knowledge, this is the first confirmed record in India of Achlya bisexualis, known in the literature as a parasite or necrotroph. Besides, neither any species of genus Achlya has previously been subjected to molecular evaluation from India.

ĐẶC ĐIỂM SINH HỌC CỦA VI NẤM Achlya bisexualis NHIỄM TRÊN CÁ NUÔI THÂM CANH

Nghiên cứu được thực hiện nhằm xác định đặc điểm sinh học của vi nấm Achlya bisexualis gây bệnh trên cá nuôi thâm canh. Tổng cộng 6 chủng Achlya bisexualis được phân lập từ cá tra (Pangasianodon hypophthalmus), cá lóc (Channa striata) và cá điêu hồng (Oreochromis sp.). Kết quả cho thấy A. bisexualis phát triển tốt trong khoảng nhiệt độ 28 - 33oC. Vi nấm có thể phát triển nhanh ở pH 6-8. Các chủng có thể phát triển đến độ mặn 1,5%. Vi nấm sử dụng carbohydrat gồm glucose, maltose, mannose, sucrose và arabinose. A. bisexualis cho phản ứng với nitrite 5mM nhưng không phản ứng với nitrite 43 mM.

An investigation into plasmolysis in the oomycete Achlya bisexualis reveals that membrane–wall attachment points are sensitive to peptides containing the sequence RGD and that cell wall deposition can occur despite retraction of the protoplast

The structure and function of membrane–wall attachment sites in walled cells, and how these relate to animal focal adhesions, is an area that is poorly understood. In view of this, we investigated how membrane–wall attachments that form upon plasmolysis, respond to peptides that disrupt animal focal adhesions. The degree of cytoplasmic disruption during plasmolysis was also investigated. Upon hyperosmotic challenge, the protoplast in hyphae of the oomycete Achlya bisexualis typically retracted incompletely due to membrane–wall attachments. The inclusion, in the plasmolysing solution, of peptides containing the sequence RGD disrupted these attachments in a dose-dependent manner. In some hyphae, protoplast retraction stopped temporarily at attachment points — upon resumption of retraction, material was left that traced the outline of the static protoplast. Staining of this material with fluorescence brightener indicated the presence of cellulose, which suggests that wall deposition was able to occur despite plasmolysis. The F-actin cytoskeleton was disrupted during plasmolysis; peripheral F-actin staining was observed, but there was no distinct F-actin cap; staining was more diffuse; and there were fewer plaques compared with nonplasmolysed hyphae. Our data indicate that membrane–wall attachment points are sensitive to RGD-containing peptides and that wall deposition continues despite protoplast retraction and F-actin disruption.