Straminipilous organisms from fallen mangrove leaves from Panay Island, Philippines

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1 Straminipilous organisms from fallen mangrove leaves from Panay Island, Philippines Eduardo M. Leaiio Aquaculture Department, Southeast Asian Fisheries Development Center, Tigbauan, 5021 Hoilo, Philippines; Leafio, E.M. (2001). Straminipilous organisms from fallen mangrove leaves from Panay Island, Philippines. Fungal Diversity 6: Fallen senescent mangrove leaves from three marine mangrove sites in Panay island, Philippines were collected for observation and isolation of straminipilous organisms. A total of 11 mangrove species were sampled. Halophytophthora species were observed on 7 out of 11 mangrove species sampled, with H. vesicula as the most abundant species observed. Halophytophthora epistomium also occurred abundantly on fallen leaves of Rhizophora apiculata and Sonneratia sp. Thraustochytrids, on the other hand, were observed on all mangrove leaf samples ecept Aegiceras corniculatum. Schizochytrium mangrovei was the most abundant species observed. Their association and ecological role on the degradation of fallen mangrove leaves is discussed. Key words: Halophytophthora, mangrove, thraustochytrids. Introduction Marine straminipilous organisms (oomycetes and thraustochytrids) are associated with decomposition of leaf materials in the aquatic habitats. In the mangrove environment, fallen leaves are colonised by microorganisms, and release abundant organic matter upon degradation. Oomycetes and thraustochytrids are common colonizers of fallen mangrove leaves, and are associated from early to late stages of decay (Bremer, 1995; Nakagiri et al., 1989; Leaiio et al., ]998). They are also reported to play an important role in the food web of estuarine ecosystem (Nakagiri, ] 993) being secondary producers in coastal zones where there is high productivity by vascular plants (Newell, 1996). These straminipilous organisms are ubiquitous in marine and estuarine environments, in tropical and sub-tropical areas (Newell and Fell, 1992). This study was conducted to determine the abundance of oomycetes and thraustochytrids on fallen mangrove leaves from Panay island in the Philippines. 75

2 Materials and methods Sample collection Fallen senescent leaves of 11 mangrove species (Table 1) were collected from three marine (salinity range: %0) mangrove sites in Panay Island: Ibajay and Dumaguit, Aklan; and Banate, Hoilo. At least 10 leaf samples were collected for each mangrove species per sampling (three samplings in Ibajay; two in Banate; and one in Dumaguit). The leaves were placed in plastic bags upon collection and returned to the laboratory for observation and isolation of straminipilous organisms. Table 1. Mangrove species sampled at different sampling sites in Panay island, Philippines. Mangrove species Aegiceras corniculatum (L.) Blanco Avicennia lanata L. A. officinalis L. Bruguiera cylindrica (L.) BI. Camptostemon philippinense (Vidal) Becc. Ceriops decandra (Griff.) Ding Hou Heritiera littora/is Dryand. E. W. Ait. Rhizophora apicu/ata BI. Sonneratia sp. Xylocarpus granatum Roem. X. mekonfiensis Pierre Ib~ Mangrove sites Dumaguit Banate Isolation The leaves were cut into 1 cm2 pieces (5-10 pieces/leaf sample) and washed three times (lh/wash) in sterile natural seawater (NSW) supplemented with antibiotics (ab: 1000 U/mT. of Penicillin G and 500 Jlg/mL Streptomycin sulfate). For thraustochytrids, four leaf pieces were inoculated onto yeast etract-peptone (YEP) agar [composed of 1 gyeast etract (BBL), 1 g mycological peptone (Ooid), 15 g agar (BBL), 1 L NSW] with ab, and flooded with thin layer of sterile NSW with ab. Two YEP plates were prepared per leaf sample. The plates were incubated at room temperature (ca QC) for 2-3 d. Growth of thraustochytrids were monitored daily and selected colonies were picked with fine-tipped forceps. The isolates were purified on YEP agar. For Halophytophthora species, the 2-4 leaf pieces (per leaf sample) were inoculated on sterile NSW at room temperature for 5 d. Zoosporangial production was monitored daily. Individual zoosporangium of selected isolates were picked and inoculated onto peptone-yeast etract-glucose-seawater 76

3 (PYGS) agar [composed of 1.25 g mycological peptone, 1.25 g yeast etract, 3 g glucose (Aja), 12 g agar, IL NSW] supplemented with ab. The isolates were purified on fresh PYGS agar. Identification Thraustochytrid isolates were identified using the pine-pollen culture and based on cell and zoosporangial characteristics described by Booth and Miller (1968), Raghukumar (1988), and Honda et al. (1998). Halophytophthora species were identified based on zoosporangial characteristics using the identification scheme by Ho et al. (1991). Results and discussion Straminipilous oomycetes and thraustochytrids are widely distributed in many mangrove habitats in tropical and sub-tropical areas. This include Japan (Nakagiri et al., 1989), Bahama islands (Newell and Fell, 1992), Taiwan (Ho et al., 1991), India (Raghukumar, 1988), Malaysia (Bremer, 1995), and Hong Kong (Leafio et al., 1998) among others. This study is the first report on the occurrence of Halophytophthora species and thraustochytrids from the Philippines. Table 2 shows the abundance of Halophytophthora species and thraustochytrids observed on fallen leaves from Panay island mangroves. Halophytophthora species were observed on 7 out of 11 mangrove species sampled. Halophytophthora vesicula (Anast. and Church!.) H.H. Ho and Jong (Figure 1) was the most dominant species observed with frequencies of occurrence from 85 to 100%. Halophytophthora epistomium (Fell and Master) H.R Ho and Jong was observed abundantly on fallen leaves of Rhizophora apiculata (77%) and Sonneratia sp. (60%). Other species observed were H. kandeliae H.H. Ho, RS. Chang and S.Y. Hsieh on leaves of Avicennia lanata, R. apiculata and Sonneratia sp., H. spinosa var. lobata (Fell and Master) H.H. Ho and Jong on Xylocarpus mekongensis, and H. bahamensis (Fell and Master) RH. Ho and Jong and an unidentified species on A.lanata. Halophytophthora species are pythiaceous oomycetes that inhabit marine and brackish water environments (Nakagiri, 1998). They are the primary group involved in the colonization of detached and submerged mangrove leaves (Newell and Fell, 1992). Several reports show that H. vesicula is the most dominant species observed on several mangrove species (Nakagiri et al., 1989; Newell and Fell, 1992). The dominance of this species over other fungal species was attributed to: (i) abundant zoospore production (Nakagiri et al., 1989); (ii) wide tolerance to salinity and temperature (Nakagiri, 1993; Leafio, et al., 1998); (iii) ability to compete against higher fungi in colonizing mangrove leaves (Newell and Fell, 1997); and, (iv) the ability of the zoospores 77

4 to attach firmly on the substrata surface for successful germination and colonization (Leafio et al., 2000). Moreoever, H. vesicula was found to produce enzymes (e.g. cellulase, pectic lyase, polygalacturonase) necessary for the degradation of a wide variety of organic compounds present in mangrove leaves (Raghukumar et al., 1994). Among the thraustochytrids, all leaf samples collected ecept Aegiceras corniculatum yielded few to abundant colonies (Table 2). Schizochytrium mangrovei Raghuk. (Figure 2) was the most abundant species observed with frequencies of occurrence ranging from 40 to 100%. Thraustochytrium sp. was also observed on leaves of X. granatum (abundant) and R. apiculata (few). Table 2. Abundance of Halophytophthora and thraustochytrids on fallen mangrove leaves from Panay island, Philippines. Mangrove species Aegiceras corniculatum Avicennia lanata A. officinalis Bruguiera cylindrica Camptostemon philippinense Ceriops decandra Heritiera littoralis Rhizophora apiculata Sonneratia sp. Xylocarpus granatum X. moluccensis Frequency of Occurrence (%)* Halophytophthora Thraustochytrids H. vesicula (94) H. kandeliae (28) H. bahamensis (12) Halophytophthora sp. (5) H. vesicula (loo) H. vesicula (95) H. vesicula (100) H. epistomium (77) H. kandeliae (15) H. vesicula (85) H. epistomium (60) H. kandeliae (25) H. vesicula (loo) H. epistomium (20) H. vesicula (100) H. spinosa var. lobata (5) Schizochytrium (100) mangrovei S. mangrovei (83) Schizochytrium sp. (l0) Schizochytrium sp. (15) S. mangrovei (75) S. mangrovei (loo) Schizochytrium sp. (7) Thraustochytrium sp. (15) Schizochytrium sp. (5) S. mangrovei (90) Schizochytrium sp. (20) Thraustochytrium sp. (70) S. mangrovei (65) S. mangrovei (40) * Number of specific straminipilous organism observed Total number ofleaf samples collected (per mangrove species) 100% Thraustochytrids are widely distributed in saline lakes, as well as marine and estuarine waters (Naganuma et al., 1998). They are reported to be associated with mangrove swamps (Ulken, 1981), seawater (Honda et al., 1998), marine sediments (Raghukumar, 1980), and littoral algae and seaweeds 78

5 Figs Dominant species ofstraminipilous organisms from fallen mangrove leaves in Panay island, Philippines. 1. Halophytophthora vesicula. 2. Schizochytrium mangrovei (c = mature cell; t = tetrad; 0 = octad). Bars: 1 = 20 IJm, 2 = 10 IJm. (Miller and lones, 1983). Unlike Halophytophthora species, however, few reports are available on their association on fallen mangrove leaves. Raghukumar (1988) reported the presence of S. mangrovei on fallen leaves of R. mucronata Lam. and A. officinalis. Thraustochytrids were also found colonizing fallen senescent leaves of Sonneratia and Rhizophora (Bremer, 1995). Results from this study show that thraustochytrid species can also colonize a wide variety of mangrove leaf species once fallen into the water (Table 2). Thraustochytrids play an important role in the aquatic food web through their degradative activities (Ulken, 1981). Raghukumar et al. (1994) reported that S. mangrovei secretes high amounts of degradative enzymes including amylase, cellulase and polygalacturonase. In addition, many species of Schizochytrium and Thraustochytrium are efficient producers of polyunsaturated fatty acids including decosaheaenoic acid (DHA) and eicosapentaenoic acid (EPA) (Yaguchi et al., 1997). In general, oomycetes and thraustochytrids as detrital microbes, play a major role in altering the chemistry of detritus (Raghukumar et al., 1994) especially fallen leaves in mangrove environments. As early colonizers, they degrade a wide variety of organic compounds (Raghukumar et al., 1994) thus 79

6 enriching the nutrient of the leaves with their biomass (Nakagiri, 1998). This process changes the plant debris into a nutritious form for consumption of organisms in higher trophic levels. Therefore, the degradation and enrichment of fallen mangrove leaves by these microorganisms contribute significantly on the nutrition of many bottom-feeding and filter-feeding organisms, making mangroves as ecellent nursery grounds for many fish and crustacean species. Acknowledgements This study was funded by SEAFDEC/AQD under study code Nr-05-F99T. The author wishes to thank K.W. Fan of City University of Hong Kong for assistance in the identification of thraustochytrid isolates. References Booth, T. and Miller, C.E. (1968). Comparative morphologic and taonomic studies in the genus Thraustochytrium. Mycologia 60: Bremer, G.B. (1995). Lower marine fungi (Labyrinthulomycetes) and decay of mangrove leaf litter. Hydrobiologia 295: Ho, H.H., Chang, H.S. and Hsieh, S.Y. (1991). Halophytophthora kandeliae, a new marine fungus from Taiwan. Mycologia 83: Honda, D., Yakochi, T., Nakahara, T., Erata, M. and Higashihara, T. (1998). Schizochytrium limacinum sp. nov., a new thraustochytrid from a mangrove area in the West Pacific ocean. Mycological Research 102: Leafio, E.M., Jones, E.B.G. and Vrijmoed, L.L.P. (2000). Why are Halophytophthora species well adapted to mangrove habitats? In: Aquatic Mycology Across the Millenium (eds K.D. Hyde, W.H. Ho and S.B. Pointing). Fungal Diversity 5: Leafio, E.M., Vrijmoed, L.L.P. and Jones, E.B.G. (1998). Physiological studies on Halophytophthora vesicula (straminipilous fungi) isolated from fallen mangrove leaves from Mai Po, Hong Kong. Botanica Marina 41: Miller, J.D. and Jones, E.B.G. (1983). Observations on the association of thraustochytrid marine fungi with decaying seaweed. Botanica Marina 26: Naganuma, T., Takasugi, H. and Kimura, H. (1998). Abundance of thraustochytrids in coastal plankton. Marine Ecology Progress Series 162: Nakagiri, A. (1998). Diversity of halophytophthoras in subtropical mangroves and factors affecting their distribution. Proceedings of the Asia-Pacific Mycological Conference on Biodiversity and Biotechnology. Hua Hin, Prachuapkhirikhan, Thailand: Nakagiri, A. (1993). Growth and reproduction of Halophytophthora species. Transactions of the Mycological Society of Japan 34: Nakagiri, A., Tokumasu, S., Araki, H., Koreeda, S. and Tubaki, K. (1989). Succession of fungi in decaying mangrove leaves in Japan. In: Recent Advances in Microbial Ecology (eds T. Hattori, Y. Ishida, Y. Moruyama, K. Morita and A. Uchida). Japan Scientific Society Press, Tokyo: Newell, S.Y. (1996). Established and potential impacts of eukaryotic mycelial decomposers in marine/estuarine ecotones. Journal of Eperimental Marine Biology and Ecology 200:

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