Marine Sponge: Sponge-Bacteria Association
Marine Sponges Niche
Overview of Marine Sponges
Marine sponges are natural bath sponges (with living cells removed) that we all are familiar with. They actually are the oldest and simplest animals that have been living on earth for millions of years. There are various types of sponges under Phylum PORIFERA. They grow in every ocean in the world regardless of extreme temperatures. They can be found hundreds of meters under sea level but mostly are found in 5-50 meters deep. Marine sponges are filter-feeding animals because all adult sponges are sessile and can’t move around benthic surface. For approximately 20 centimeters sponge can filter up to 2000 liters of seawater during one day. “As filter feeders, sponges efficiently take up nutrients like organic particles and microorganisms from the seawater, leaving the expelled water essentially sterile.” (3) Marine sponges have no true tissues or organs, just constructed with layers of cells even without nervous system. Inside the sponge, the vibration of ciliates, the special cells circulate seawater through small pores and absorb planktons and small sea organisms. (1)
Marine sponges come in different but striking colors, bright red, purple, yellow, and brown, etc. These colors and some are toxic as well may help them defend from sponge eating invertebrates and some fishes. Some other small marine organisms, fishes, and microscopic organisms often call marine sponges their homes. Sponges often have skeleton of spicules, which protect and give refuge to small invertebrates from other marine scavengers. (2)
Living Conditions/Locations
The optimal growth temperature of the marine sponge in its natural habitat is ranging 8C ~18C. Also, the most of the marine sponges’ optimal pH is around 6.5 because the pH value of the sponge cellular fluid is 6.5. However, some sponges can live in the extreme temperature and pressure. For example, the bright red antarctic sponges, Kirkpatrickia Variolosa (K. Variolosa) are found in deep sea of the isolated Antarctic continent, where Antarctic Circumpolar Current is present. It is a rare type of sponge found only in 0.02% of benthic surface at Cape Armitage site but can be seen typically in other areas as deep as 100-700 meters. (9) Beyond living in the deep sea, K. Variolosa withstand high pressure and freezing temperature below 0 degree Celsius. The sea temperature may vary from -2 to 10 degree Celsius.
Adjacent Communities
The community of K. Variolosa includes spongivorous sea stars, “other sessile and sluggish marine invertebrates, and a sponge feeding nudibranch. However, the main predators of K. Variolosa being the sea stars Perknaster fuscus and Acodontaster conspicus. (10) As a predator-prey interaction, sea stars eat larvae of sponges in order to prevent biomass of sponges on benthic surface. However, as a rare species, K. Variolosa had invented toxin to defend itself from chewing up by the omnivorous sea stars.
No matter how powerful its toxin is, K. Variolosa is beyond help when natural disaster and abiotic factors hit its community. Humongous iceberg and anchor ice can scour the entire community of K. Variolosa. Unpredictable currents and various types of sedimentation also determine the habitat of K. Variolosa. (10)
Type of Sponges
- Location: Caribbean and Mediterranean; shallow rocky substrates exposed to light (1-20m depth)
- Characteristics/Physical conditions:
- - usually sulfur-yellow in color but can be tinged toward green or red
- - sponge fibers made up of laminated,golden-bark and a granular, dark pith
- - can protect large number of bacteria that can take up to 40% of its mass
- - alternate between high water-pumping speed and low water circulation phase
- - produce brominated aromatic mebolites such as bormoindoles, bromophenol(BP), polybrominated diphenyl ethers, and dibromodibenzo p-dioxins (can serve as a chemical defense against predators and biofouling)
- Location: reef environments of Florida and the Caribbean
- Characteristics/Physical conditions:
- - lamellate barrel- or volcano-shaped sponge
- - salmon to purple (presence of cyanobacterial symbionts in the ectosome)
- - produce different kinds of straight-chain actylenic compounds, which have antimicrobial and cytotoxic properties
- Location: Caribbean and Australia
- Characteristics/Physical conditions:
- - color is usually red, orange, or yellow (15)
- - should never exposed to the air because it will block the pathway for planktonic to reach its cells (15)
- - filter feeder (require daily feedings of plankton substitutes and dissolved organic foods (15)
- - can be characterized by the presence of terpene metabolites (18)
- Location: Sea of Okhotsk and North Pacific (shallow water)
- Characteristics/Physical conditions:
- - surface smooth shiny; its body shape is irregular: encrusting, pillowy or clotted in form
- - soft and very delicate (can be easily torn)
- - released larvae during the period of temperature maximum (typical for marine hydrobionts in cold waters
Microbes
Diversity
Various microorganisms have been found in sponges. They include a diverse range of green algae, heterotrophic bacteria, cyanobacteria, archaea, cryptophytes, red algae, dinoflagellates and diatoms. The symbiotic microbial community is a highly diverse society. One host sponge can possess diverse symbionts. For example, sponge Theonella swinhoei incorporates unicellular heterotrophic bacteria, unicellular cyanobacteria and filamentous heterotrophic bacteria all at the same time(21). Some of the symbionts inhabit specific sponges while others do not. For example, a species of δ-proteobacteria and the sponge Theonella swinhoei show a specific association(22). Some sponges have a dominant symbiotic microorganism. For example, a species of α-proteobacteria dominates in sponge Rhopaloeides odorabile over various habitats but is not detected in seawater, which is an indication that the symbiont is sponge-specific.
Cyanobacteria are aquatic and photosynthetic, and despite the fact that cyanobacteria and algae are not closely related, cyanobacteria are often called "blue-green algae" because of their common characteristic of being aquatic, photosynthetic, and superficial similarity. Cyanobacteria are usually unicellular, but often they grow in colonies. They are also the oldest known fossil, which is more than three billion years old. Cyanobacteria are considered as the origin of plants because the chloroplast in plant cells that produce food source for themselves is actually a cyanobacterium that live within the plant cells. Because of their ability to photosynthesize, even though cyanobacteria are prokaryotes, they have highly organized and complex system of internal membranes, which can be analogue to eukaryotic thylakoid membranes.
Either biofilm or planktonic form of a gram-negative proteobacteria, Pseudomonas aeruginosa is known to colonize the surfaces of K. Variolosa. Although this bacteria is opportunistic pathogen to human diseases such as urinary infection, respiratory system infections, dermatitis, bone and joint infections, and gastrointestinal infections, it is symbiotically good for K. Variolosa. (11) P. Aeruginosa produces antibiotic compounds such as diketopiperazines and two other phenazine alkaloid antibiotics. These antibiotics inhibit the growth of several gram-positive microorganisms. (12) This bacteria in turn have known to receive acetate and other carbon sources as nutritions from K.Variolosa.
The Chloroflexi line of descent is thought by many to have diverged early in the evolution of the domain Bacteria (1). Chloroflexi- related sequences occupy a wide variety of habitats: geothermal, soil, freshwater, marine, wastewater, and subsurface environments. In addition, Chloroflexi exhibits a diverse range of phenotypes, including anoxygenic photosynthesis (e.g., Oscillochloris and Chloroflexus) (2), thermophilic organotrophy (Thermomicrobium), and chlorinated hydrocarbon reduction (Dehalococcoides ethenogenes). (3)
Sponge-Microbe Association
Microbial Metabolism of Sponges, Mutualism/Commensalism
There is a mutual relationship between cyanobacteria and marine sponge. While Cyanobateria provide nutrients to sponge, sponge provides a shelter for bacteria. For example, sponges that live in tropical regions depend heavily on cyanobacteria for their nutrient source. More that 50% of their energy requirement is fulfilled by photosynthetic metabolism of cyanobacteria. The energy gained from this metabolism are used in various ways, from longetivity of sponges when they are in gametes and larval period, to the rapid growth of the sponges to compete with other organisms such as algae. There was an experiment performed to show how cyanobacteria benefits the sponges. The tropical sponge Lamellodysidea Chlorea, which contains host-specific cyanobacterium Oscillatoria spongeliae, was shaded partly to inhibit illumination. The result showed that shaded part of the sponge lost more than 40% of its initial region, while illuminated region did not have any change. This result indicates that photosynthesis of cyanobacteria has significant effects on growth of sponges.
On the other hand, however, due to its high photosynthetic rate, cyanobacteria in marine sponge can overwhelm the host tissues if they are grown without control. Thus, the host sponges are believed to have a few mechanisms of controlling the growth of cyanobacteria such as stealing photosynthate from them and starving the symbiont.
Cyanobacteria not only perform photosynthesis to provide energy, but also are capable of nitrogen fixation. The activity of nitrogenase, which is the catalyst for microbial nitrogen fixation, was only found in the sponges that contained cyanobacteria. In addition, the activity of nitrogenase was higher in the region that was illuminated than in the region that did not get enough light. This fact indicates that the activity of nitrogenase is mainly dependent upon the presence of cyanobacteria. Taken all together, the metabolism of photosynthesis and activity of nitrogenase are the key sources that allow marine sponges with cyanobacteria to live in a nutrient deficit region, such as in the tropical reefs.
Mutualistic organism lives within K. Variolosa is diatoms. The outer coverings of diatoms are made up of silica. K. Variolosa absorb and digest silica for its spicules and in return provides shelter for diatoms from other predators.
The Chloroflexi, also known as green nonsulfur bacteria, are typically filamentous, gram negative bacteria, which move via bacterial gliding. With the characteristic of aerobic, they produce energy through photosynthesis but do not produce oxygen and have different carbon fixation method (photoheterotrophy). For example, they use light for energy, but cannot use carbon dioxide as their carbon source, so they use carbons from other bacteria or host organism. Therefore, Chloroflexi use compounds such as carbohydrates, fatty acids and alcohols for the organic food. Also, they use hydrogen as the sole electron donor instead of water and carbon dioxide the sole electron acceptor for photoautotrophic growth. (4) Furthermore, Chloroflexi grows by fermentation of sugars such as sucrose, yielding acetate and hydrogen as the main end products. (5) Through the fermentation Chloroflexi produces ATP through the fermentation to use as an energy source for biosynthesis and reproduction.
A benefit of Chloroflexi living on the marine sponge especially in Spongilla lacustris, is the mere protection by the sponge and escape from the grazing pressure in the environment. This holds true only when a balance exists between bacterial growth and digestion by the sponge. Also, Chloroflexi gets most of the sugars (sucrose) by the marine sponge host, and use that carbon source for both photosynthesis and fermentation. Benefit for the marine sponge is that Chloroflexi provides energy to the marine sponge to grow.
Pathogens/Parasites
Some of the deleterious effects of microbes on sponges may be direct(parasitism and pathogenesis) or indirect(surface fouling promoted by biofilm). As an example of a pathogenic effect of microbe, alphaproteobacterium was studied from an infected individual of the Great Barrier Reef sponge Rhopaloeides odorabile (16) was shown to infect and kill healthy sponge tissues. The mechanism used by the pathogen was to degrade collagenous spongin fibers, with almost the entire sponge surface subject to tissue necrosis. This pathogenesis occured not only in marine sponges, but also corals and other epibenthic organisms in 1999 when these organisms experienced massive mortalities(17). This outbreak of the disease coincided with rise in water temperature around the region, suggesting that protozoan and fungi also were involved. Other reports of diseases in sponges include the Aplysina red band syndrome, cyanobacterial overgrowth of Geodia papyracea, and repeated observations of diseased sponges on a Panamanian coral reef.
Parasitism of sponges by diatoms were found in several Antarctic species. Degradation of sponge internal tissue occured in areas of dense diatom aggregations. The diatoms in "S. joubini" appeared to enter the host either through the ostia (inhalant openings) or via active incorporation by the sponge pinacoderm(dermal membrane). Reseason why sponges incorporate these potentially harmful diatoms is not yet clarified. A plausible explanation is that sponges consume diatoms as a food source.
Some of the non-harmful bacteria can also harm the sponge in an indirect-manner. Microbes form colonies on the surface of the sponge by microbial fouling. This fouling can act as a precursor to colonization of macrofouling organisms, such as, invertebrates and macroalgae, which can potentially affect sponge's nutrition intake by blocking the feeding channel or cause dislodgement of the sponge from the substratum by increasing the hydrodynamic drag.
Interactions with Other Organisms
The relationship between marine sponges and other organisms can be summarized in to three different categories, which are competition, predation, and symbiosis. First, competition between sponges and other organisms are likely to be influenced by chemical factors. For example, allelochemicals help sponges to outgrow bryozoan by inhibiting its metabolism. Invertebrate species such as crustaceans and asteroid are the predators of marine sponges in temperate water. These species prefer to consume tissues with cyanobacteria, thus they are likely to consume sponges in shallow water, which contain a lot of cyanobacteria. Lastly, the sponges have symbiotic relationship with other organisms. For example, sponges living on scallops provide protection from starfish predators, and prevent damages in scallop shell, while the sponges gain favorable living space.
K. Variolosa, a sponge, is a filter feeding animal and basically immobile. They generally rely on cyanobacteria, autotrophs, which synthesize complex carbon compound using light energy. When there are long days without sun light in South pole Antarctica, the sponge has to rely on filtering any type of organic debris passed by. It is also observed that some other sponge family has evolved into heterotrophy and developed to move other places to feed.
Current Research
1. ITS-2 and 18S rRNA Gene Phylogeny of Aplysinidae (Verongida,Demospngiae), 2004
In order to identify the genus-level for sponges(Porifera) taxonomy, the researchers have been using their characteristics such as spicules and sponging fibers. However, it became noticeable that having a precise taxonomical classification of the Porifera was difficult especially if sponges were being identify only by using their morphological features. Therefore, this research was conducted to investigate if there is any other way to have a get a clear genus-level of different sponges. It revealed that matching up 18S ribosomal DNA and internal transcribed spacer 2 (ITS-2) full length sequences to certain marine sponge sequence can be used to build phylogenetic trees to arrange based on secondary structure. For this experiment, different sponges were analyzed such as eleven Aplysina sponges and three additional sponges (Cerongula gigantean, Aiolochroia crassa, Smenospongia aurea) from different location such as tropical and sub-tropical oceans. The results concluded that Aplysinais from a single common ancestor and stands at a basal position in both 18S and ITS-2 trees. The problem with this method is that the molecular data come out differently from the current taxonomy that was structured based on morphological characteristics. Therefore, the future research is to reevaluate the sponges as more 18S sequences become available. (7)
2. Biodegradation, 2003
Halogenated compounds are one of the biggest environmental pollutants on earth. In order to degrade these harmful bio-reactive materials, naturally occurring biodegradable compounds are needed. Marine sponges naturally produce brominated organic compounds for chemical defense against predators and biofouling. A bright yellow sponge family, Aplysina aerophoba constitutes 7-12% of bromine-containing metabolites in its dry weight. (4) They are abundantly found in subtropical and tropical waters of the Mediterranean Sea and Pacific and Atlantic oceans. The major secondary metabolites of this sponge are bromophenolic metabolites derived from dibromotyrosine. Interestingly, A. aerophoba is also a host to diverse microorganisms, which constitute 40% of its biomass. While the brominated compounds released by A. aerophoba are harmful to others but not to these microbial community is an inspired research for scientists.
The scientists are working on sponge-associated microorganisms that might have the ability to dehalogenate and degrade brominated compounds. They have isolated “a conserved reductive dehalogenase gene motif in the dehalorespiring bacteria D. ethenogenes, Dehalospirillum multivorans, and Desulfitobacterium dehalogenans.” (4) These dehalogenating bacteria debrominate the brominated compounds by anaerobic reductive activities. They are anaerobic because “most sponges alternate between periods of high water-pumping velocity and periods of low water circulation. It is possible that oxygen becomes limited during periods of low water circulation because of active respiration by the large number of bacteria present in the mesohyl, sponge’s gut.” (4) The diversity of genes motifs isolated from these bacteria is valuable for environmental biodegrading. Therefore, marine sponges along with dehalogenating bacteria serve as cues for scientific community to explore more about marine sponge and its valuable natural biodegrading compounds.
3. Vertical Transmission, 2007
Marine sponges are hosts to plenty of microbial organisms in their inner lining, mesohyl. These micro bacteria are sponge-specific and have been passed on generations after generations. In addition, microbial biomass in marine sponges contributes up to 40% to 60% of sponge’s biomass. (3) “No other animal phylum tolerates such amounts of internal, freely dispersed microorganisms.” (3) Since marine sponges do not have physical barriers, such as tissues or organs, different types of microorganisms living within the marine sponge are important to study “cospeciation” between the host and many symbiotic lineages. In ball-shaped sponge, Ircinia felix, vertical transmission of microorganisms were observed in larvae form of the sponge. Vertical transmission is “a passage of microbial symbionts to the next host generation through the reproductive cell lines.” (3)
In I. felix, vertically transmitted phylotypes are “defined as monophyletic clusters of two or more sequences that were recovered from both the adult sponge and offspring. Altogether, 13 monophyletic sequence clusters were identified, which belonged to four different bacterial phyla and one additional lineage of uncertain affiliation.” (3) Interestingly, the scientists found out that the vertical transmission of bacterial community in adult I. felix was similar to those well-studied symbionts of sponge-associated bacteria such as Proteobacteria (Alphaproteobacteria, Gammaproteobacteria, and Deltaproteobacteria), Acidobacteria, Actinobacteria, Bacteroidetes, Chloroflexi, and Cyanobacteria. However, it is still a wonder and extremely complex for scientific community to find out how this “unique and apparently stable sponge-microbe associations are established and maintained over time.” (3) If we can find out the clues, we will have another way to hypothesize how life originated on earth.
4. Anti-Cancer Drugs
K. Variolosa, the colorful bright red sponge, has known to produce anti-cancer drugs. The rare coloration of this sponge is not only to camouflage itself from predators and defending itself by showing off its angry-looking color, the pigment is useful in human medicine. Pigments from the colored sponges are bioactive and cause sea star tube-foot retraction. A anti-cancer drug, a compound Variolin-B (VAR-B), is isolated and “prevents the cancer cells from entering S-phase, blocking cells in G1 and cause an accumulation of cells in G2. It inhibits CDKs and induces apoptosis. This drug is also useful for anti-tumor and antiviral activity. (13)
5. Anti-HIV products
A marine sponge, Monanchora unguifera, produces anti-HIV products derived from alkaloids, Batzelladine alkaloids. Batzelladines interfere with protein-protein interactions including HIV-1 gp120-human CD4. “The process of HIV-1 infection is initiated by attachment of HIV-1 to cells through a high affinity interactions between viral envelope gp120 and CD4 receptor on the surface of a T cell.” [19] The derivatives of Batzelladine alkaloids deter the binding of gp120 to CD4; therefore, blocking the entry of viral DNA and inhibiting the replication inside the host cells.
Another synthetic analogs of Batzellidine are guanidines, which “inhibit the Nef-ligand interactions with IC50 values in the low micromolar range.” [20] The hydrophobic rings surrounding the planar guanidine are able to disrupt the large and flat surfaces of protein-protein interactions. However, current treatments do not target all HIV proteins and a large number of active compounds have yet to be identified. [20]
Summary
The marine sponges belong to the Phylum Porifera in which is located in every ocean. They have similar function but are identified in different genus level by different colors and structures. These morphological features are being shown due to the different bacteria such as proteobacteria, cyanobacteria, chloroflexi, and etc. Therefore, these bacteria will give necessary characteristics and functions to the sponges and in a return; they will get a shelter to reproduce. It is not only bacteria that occupy the marine sponge but also fishes, fungi, corals, and etc in which help sponges’ activities. The marine sponges are known as species in the ocean but recently researchers are discovering that it can be anti-cancer drugs.
References
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Edited by Thomas Kim, Woo Lee, Jessica Na, Francis Wong, Sungjun Yoon (Students of Dr. Rachel Larsen - UCSD Summer Session II 2008)
