Zoospore production and motility of mangrove thraustochytrids from Hong Kong under various salinities

Abstract

We investigated the effects of salinity on the zoospore production of four mangrove thraustochytrid isolates, Schizochytrium sp. KF1, Aurantiochytrium mangrovei KF6, Thraustochytrium striatum KF9 and Ulkenia sp. KF13. The zoospore motilities, which were based on curvilinear velocity (VCL) and straight-line velocity (VSL), were monitored using the Computer-Assisted Sperm Motility Analysis (CASA) Software system. The zoospore production of four isolates was suppressed at salinity above 15%. Schizochytrium sp. produced the greatest number of zoospores at 15%, while Aurantiochytrium mangrovei and Ulkenia sp. produced abundant zoospores in diluted sea water ranging from 7.5 to 15%. Thraustochytrium striatum performed relatively poorly under all salinities. Salinity and exposure time, as well as their interactions, had significant impacts on most zoospore velocity measurements. The optimal velocities of zoospore motility also varied among isolates. Zoospores of Schizochytrium sp. and A. mangrovei had similar responses to salinity, with the highest motility at 7.3%, followed by a decrease in velocities with increasing salinity. In contrast, the zoospore of T. striatum had optimal motility at 12% and remained highly motile from 15 to 20%. The velocities of zoospores of Ulkenia sp. were the lowest among the tested thraustochytrids and had optimal motility at 12%. Zoospores of all the isolates remained active after 4 h of exposure to aqueous medium, but the optimal salinity for each mode of swimming changed. The ecological significance of these data are discussed.

A Re-Visit to the Evolution and Ecophysiology of the Labyrinthulomycetes

“…fatty acids -Fan et al, 2001-Fan et al, , 2007squalene -Li et al, 2009). In the following paragraphs, a review of some ecophysiological investigations of thraustochytrids isolated from decaying mangrove leaves in subtropical mangroves is presented (Fan et al, 2002a, b, Tsui et al 2011, Wong et al, 2005.…”

“…A series of ecological and physiological investigations have been undertaken on various isolates of thraustochytrids isolated from the subtropical mangroves where salinity levels could vary between 5 and 34 ‰ in summer and winter in Hong Kong respectively (Fan et al, 2002a, b, Tsui et al, 2011, Wong et al 2005. Some of these species were isolated from low saline waters (ca.…”

“…The zoospore production capacity and their motility profile are also highly influenced by salinity (Tsui et al, 2011). A summary of the zoospore features at various salinities of Schizochytrium sp.KF1, Aurantiochytrium mangrovei KF-6, Thraustochytrium striatum KF-9 and Ulkenia KF-13.…”

“…Their VSL and VSL were high which compensate the moderate zoospore production amount and the average motility % within a 4h period. These are the probable reasons for their dominance in the subtropical mangroves in Hong Kong (Tsui et al, 2011 a The motility of zoospores was recorded using the image analysis system consisting of a phase contrast microscope with a lens at 20x10 magnification (Olympics BX50 Japan) equipped with a progressive scan charged-coupled device (CCD) camera (Basler Scout, SCA640-70FM, Ahrensburg, Germany). b Zoospores were induced from 2-day old cultures in yeast extract peptone plates flooded separately with distilled water, and artificial seawater at 7.5, 15, 22.5 and 30‰.…”

“…Table 1. A summary of zoospore profile of mangrove thraustochytrids (adapted from Tsui et al, 2011).…”