Browsing Masters Theses by Issue Date

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    • Isolation, purification and characterization of extracullular vibriolytic factors from Pseudomonas species 

      Dalisay, Doralyn ORCID (1999-04)
      Pseudomonas spp. P. aeruginosa JP4, P. aeruginosa CD2 and P. fluorescens isolated from aquatic environments produce extracellular vibriolytic factors when grown in nutrient broth. Production of vibriolytic factors was noted during the logarithmic phase of bacterial growth. Vibriolytic activity was examined based on the decrease in the optical density of a standard suspension of Vibrio harveyi, a causative agent of luminescent vibriosis in shrimp pond and hatchery systems. Five extracellular vibriolytic factors of Pseudomonas aeruginosa JP4 were isolated and partially purified by ammonium sulfate fractionation, followed by a combination of column chromatography with DEAE-Cellulose and gel filtration in Sephadex G-100. The molecular weights of the vibriolytic factors were estimated to be 27, 90, 98, 120 and 135 kDa by gel filtration column chromatography. Two of the five vibriolytic factors possessed proteolytic activity. This is the first report of vibrioytic factors of Pseudomonas aeruginosa JP4 that possess proteolytic activity at the same time. Vibriolytic activity was optimum at 30°C and pH 7.0. The vibriolytic factors were unstable to heat, and were completely inactivated when exposed to pH<4 and pH>8. The study reveals that the Pseudomonas species can possibly exert their probiotic activity by having a battery of vibriolytic factors which target V. harveyi. This provides a better understanding of the mechanism of the lytic action of Pseudomonas spp. against V. harveyi, which eventually lead to possible measures to control V harveyi infection in shrimp hatchery and pond systems.

    • Resiliency of Gracilariopsis heteroclada (Zhang et. Xia) carpospores at different salinity and temperature levels 

      Mateo, Jonalyn ORCID (2019-07)
      Environmental factors like temperature and salinity play an important role in the growth and reproduction of aquatic organisms. The change in these two factors will be a major challenge in the future. Development of different culture techniques for Gracilariopsis heteroclada (Zhang et. Xia), a species usually found in the Philippines are being undertaken due to its increasing demand, however, there is a rapid depletion of natural populations. This study tested the resiliency of Gp. heteroclada to different water temperatures and salinities. Diploid spores from mature cystocarpic thalli of Gp. heteroclada were shed and grown at different temperatures and salinities under laboratory condition. Higher germination rate was obtained at 20°C (152.21 ± 69.88 carpospores) and 30°C (155.58 ± 66 carpospores) than at 40°C (7.56±6.54 carpospores) and 10°C (no spores were shed). Carpospores shed at 40°C degraded after 3 days. Growth rates of carpospores cultured on slides at 20 °C ranged from 2.37 to 5.92% day-1 while carpospores at 30°C ranged from 2.02 to 3.44% day-1. When carpospores were transferred to aerated vessels, growth rates decreased. At 20 °C, growth rates ranged from 0.84 to 2.96 % day-1 while at 30°C, growth rates ranged from 1.65 to 2.56 % day-1. Development rates had a wide range from 0.51 to 27.27% at 20 °C while at 30 °C, development rates ranged from 1.27 to 30 %. These results showed that Gp. heteroclada can shed carpospores at a range of 20-40 °C and 20-40 ppt. However, carpospores cannot fully develop at 40 °C. Optimum temperature for growth was at 20 °C and can grow at a wide range of salinity (20-40 ppt).