Antibacterial and Anti-Diatom Activity of Hong Kong Sponges
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AQUATIC MICROBIAL ECOLOGY Vol. 38: 191–201, 2005 Published February 9 Aquat Microb Ecol Antibacterial and anti-diatom activity of Hong Kong sponges Sergey Dobretsov, Hans-Uwe Dahms, Pei-Yuan Qian* Marine Coastal Laboratory and Department of Biology, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, China ABSTRACT: In this study, we link laboratory results with field evidence of microbial settlement responses to crude extracts of several sponge species from Hong Kong waters, including Cally- spongia sp. 1, Callyspongia sp. 2, C. pulvinata, Mycale adhaerens, Haliclona cymaeformis var. 1, H. cymaeformis var. 2 and Halichondria sp. (Porifera: Demospongiae). Laboratory experiments showed that 6 out of 7 sponge extracts inhibited growth and caused mortality of the pennate diatom Nitzschia paleacea at tissue-level concentration. In disk-diffusion bioassays, extracts of the sponge Halichon- dria sp. inhibited the growth of 4 bacterial strains out of 11 isolated from inanimate substrata; other sponge extracts inhibited growth of only 1 or 2 bacterial strains. For field experiments, sponge metabolites were immobilized in a Phytagel® matrix and exposed to natural microbial communities. After 2 d of exposure, bacterial densities on the gels with sponge extracts were lower than on control gels. Terminal restriction fragment length polymorphism (TRFLP) analysis of PCR-amplified bacter- ial community 16S rRNA genes obtained from these gels demonstrated that the communities were different between the sponge extracts and control gels. After 7 d of exposure, 6 (86%) extracts suppressed the recruitment of pennate diatoms and 3 (43%) sponge extracts suppressed the recruit- ment of bacteria. These results suggest that sponge extracts can modify the structure of bacterial communities and decrease the density of bacteria and diatoms in microfouling communities. KEY WORDS: Sponge allelochemistry · Secondary metabolites · Bacteria · Diatoms · Microbial community · TRFLP · South China Sea Resale or republication not permitted without written consent of the publisher INTRODUCTION of bioactive metabolites produced either by the host itself or by symbiotic organisms (Wahl 1997, Kelly et al. Inanimate and animate surfaces in the marine envi- 2003). ronment are continuously exposed to, and colonized Sponges are a rich source of unique and diverse by, microorganisms and propagules of metacellular bioactive metabolites (Sera et al. 1999, Faulkner 2000, organisms. Bacteria and diatoms are among the first Blunt et al. 2003). Antibiotics, such as plakortin from organisms that attach to surfaces (ZoBell 1939, Plakortis halichondroides (Higgs & Faulkner 1978), Characklis & Cooksey 1983) and form natural biofilms manoalide from Luffariella variabilis (De Silva & that are highly variable over time and heterogeneous Scheuer 1980), furospongin-1 from Spongia officinalis in composition. Development of a biofilm on the sur- (Anderson et al. 1994) and aerothionin from Aplysina face of living organisms can provide advantages to the gerardogreeni (Encarnacion-Dimayuga et al. 2003) host and/or cause damage, inhibit growth, or even lead have been isolated from marine sponges. These and to necrosis and death of these organisms (Mitchell & other antibiotics isolated from marine sponges are Chet 1975, Dixon et al. 1981, Walls et al. 1993). In active against human pathogens and other bacteria invertebrates, such as sponges, the extent of microbial that are not found in the living environment of colonization is possibly influenced by chemical effects sponges. Only a few investigations, however, have *Corresponding author. Email: [email protected] © Inter-Research 2005 · www.int-res.com 192 Aquat Microb Ecol 38: 191–201, 2005 examined the antibacterial activity of secondary MATERIALS AND METHODS metabolites of sponges against bacteria isolated from marine waters (Kelman et al. 2001, Kelly et al. 2003). Collection of sponges. Specimens of the sponges Until now, there has been no experimental field Callyspongia (Cladochalina) sp. 1 (ZMAPOR 17596), evidence regarding the specific physiological effects Callyspongia (Cladochalina) sp. 2 (ZMAPOR 17598), of sponge-derived metabolic compounds on micro- Mycale adhaerens (ZMAPOR 17597), Haliclona (Gel- organisms occurring on external and internal surfaces lius) cymaeformis var. 1 (ZMAPOR 17599), H. cymae- or in the tissues of sponge. formis var. 2 (ZMAPOR 17602), Halichondria sp. In the present study, we collected 7 species of (ZMAPOR 17603) and C. pulvinata (ZMAPOR 17601) sponges from the Class Demospongiae that are com- were collected from Hong Kong coastal waters at monly found in Hong Kong coastal waters, and stud- depths of 1 to 3 m, either near the fish farm next to the ied their antibacterial and anti-diatom activity in Wong Shek Pier (22° 25’ N, 114° 20’ E), or at the fish laboratory and field experiments. Bacterial communi- farm in Port Shelter (22° 22’ N, 114° 16’ E). The sponges ties developing on gel surfaces with sponge crude were carefully retrieved to the water surface, trans- extracts were compared by the culture-independent, ferred to large buckets, and brought to the laboratory. polymerase chain reaction (PCR)-based molecular fin- The wet weight was measured at the fish farm and the gerprinting technique of terminal restriction fragment tissue volume was determined by water displacement. length polymorphism (TRFLP) (Liu et al. 1997, Harder Reference samples were stored in 96% ethanol for et al. 2004). The rationale for this approach was to subsequent taxonomic identification. Samples are held overcome the disadvantages associated with culture- in the type collection in the Zoological Museum, dependent techniques and to reveal the effects of University of Amsterdam and have the collection sponge metabolites on the formation of bacterial com- acronyms used above, i.e. ZMAPOR. munities under natural conditions. This approach Chemical extraction of sponges. In the laboratory, combines restriction fragment analysis of a phyloge- sponge tissues were extracted twice in 1:1 dichloro- netic marker with automated sequencing gel technol- methane:methanol for 8 h with gentle agitation. The ogy and permits the rapid profiling of a bacterial combined extracts were filtered through Whatman No. community. Briefly, 16S rRNA genes are PCR ampli- 1 paper filter and reduced by rotary evaporation to a fied from community DNA being directly extracted concentration that was volumetrically equivalent to from the bacterial communities developed in the 10% of the original sample tissue. Tissue-level concen- presence of sponge extracts. One primer is labeled at trations were adjusted prior to experiments. the 5' terminus with a fluorescent dye that allows the Laboratory experiments. Diatom culture: The investigator to track only the terminal fragment of a diatom Nitzschia paleacea was isolated from a natural restriction digest. As a general rule, a single species biofilm developed on microscopic slides exposed to will contribute a uniquely sized terminal fragment fouling for 5 d at the fish farm in Port Shelter. The although several species may have terminal frag- isolation was performed according to Harder et al. ments of identical size. The TRFLP method has been (2002). The diatoms were cultivated in aerated 400 ml used successfully for the characterization of bacterial Erlenmeyer flasks at 24°C with overhead fluorescent communities in marine samples (Moesender et al. illumination (0.3 × 1016 quanta s–1 cm–1). When a visible 1999, Harder et al. 2003, Qian et al. 2003, Lee & Qian film developed in the culture flask, diatom suspensions 2004) and has certain advantages over denaturing were prepared by brushing the culture flask with a gradient gel electrophoresis (DGGE) and 16S rRNA sterile paint brush. This algal suspension was then (DNA) gene cloning in terms of its effectiveness, sen- used in the following experiments. sitivity and consistency in differentiating microbial Anti-diatom bioassay: Anti-diatom activity of the communities (Moesender et al. 1999, Brodie et al. sponge extracts was tested according to a protocol 2002, Fuhrman et al. 2002). developed by Dobretsov & Qian (2002). Prior to the In this study, we proposed to determine whether (1) experiment, the sponge extracts were dried by rotary the sponge extracts affected the growth of bacteria and evaporation and re-dissolved in dimethylsulfoxide diatoms isolated from the natural environment in labo- (DMSO) to a concentration that was volumetrically ratory experiments; (2) the sponge extracts affected equivalent to 10% of the original sample tissue. the density of bacteria and diatom communities in the Extracts were tested at tissue-level concentrations. field experiments; (3) the sponge extracts affected the Three hundred µl of the extract solution were added structure of bacterial communities and the species to Petri dishes (in 8 replicates) containing 2.7 ml of composition in the field experiments; (4) the results of algal suspension of the diatom Nitzschia paleacea the laboratory experiments correspond with findings of (about 12 × 104 cells ml–1). After an incubation period the field experiments. of 2 d at 25 ± 1°C at a light:dark cycle of 15:9 h, the Dobretsov et al.: Chemical activity of sponge extracts 193 numbers of dead and living diatoms were counted on did not differ from inhibition zones of non-heated ex- 5 replicates of each plate under a light microscope tracts. A control was prepared accordingly with pure (Axiophot, Zeiss; magnification