Symbiotic Relations of Sediment‐Agglutinating Nematodes and Bacteria in Detrital Habitats: The Enzyme‐Sharing Concept

Abstract

Abstract.A new concept (`enzyme sharing') concerning the interaction of marine nematodes and microbes in the degradation of sedimentary detritus is presented. Elements of this concept are (1) the notorious tendency of many aquatic nematodes to agglutinate detrital particles by mucus secretions, (2) new observations on the stimulation of microbial growth by nematodes in agar plates, and (3) literature data on limited endogenous proteolytic capacities of aquatic nematodes.Observations on nematode-microbe associations in agar plates prompted the conceptual synthesis. In agar medium without the addition of any nutrients a spectacular growth of bacteria was visible on the sinusoidal crawling trails of nematodes only 2±3 days after introduction of the worms (species of Adoncholaimus, Anoplostoma and Sabatieria). Juveniles of Anoplostoma that hatched in the agar cultures left their minute trails in the medium and these were rapidly occupied by bacteria. The nematodes repeatedly visited their bacterial trails, which persisted as a peculiar biotic structure for more than one year and survived the nematodes.In sterile agar preparations containing the fluorogenic methylumbelliferyl-b-glucoside in the presence of the nematode Adoncholaimus, an enhanced fluorescence of the medium was visible, indicating b-glucosidase activity. We therefore assume that oncholaimid nematodes discharge enzymes that alone, or in concert with microbial activities, contribute to the hydrolytic cleavage of refractory polysaccharides containing b-glucosidic bonds such as agar components and cellulose. The sugars thus produced may then be taken up by the nematodes and concomitantly support the conspicuous growth of microbes. Since we did not observe any feeding of the nematodes on the associated microbes in agar plates, we question the nutritive potential of intact microbial cells for a U. S.

Unravelling the environmental drivers of deep-sea nematode biodiversity and its relation with carbon mineralisation along a longitudinal primary productivity gradient

“…Nematodes may influence an important ecosystem function like the bacterial breakdown of organic matter through bioturbation and irrigation (Pike et al, 2001), thereby enhancing nutrient and/or oxygen fluxes (Alkemade et al, 1992;Aller and Aller, 1992), bacterivory (De Mesel et al, 2003) or the provision of optimal growth conditions for bacteria in their mucus trails (Moens et al, 2005;Riemann and Helmke, 2002). Here, we investigated the variation in nematode taxon (genus) and functional diversity along longitudinal (reaching from the Galicia Bank in the Northeast Atlantic to the eastern Mediterranean Basin) and bathymetric (1200-1900-3000 m) gradients within deep-sea sediments.…”

Do nematode mucus secretions affect bacterial growth?

“…Alternatively, Adoncholaimus, and perhaps other nematodes, may produce exo-enzymes, which can start the initial decomposition of complex molecules. This would promote establishment and growth of bacterial populations that take over organic matter decomposition, with both nematodes and bacteria then feeding on the nutritious 'soup' of dissolved (DOM) and small particulate organic matter released from this shared use of enzymes (Riemann & Helmke 2002).…”

“…In addition to benefiting from any exo-enzymatic activity in the mucus (Riemann & Helmke 2002), bacteria may simply use the mucus for attachment or feed on it. The composition -and potential nutritive value for bacteria -of the nematode mucus is poorly known, but it does apparently contain a substantial share of acid mucopolysaccharides (Nehring et al 1990).…”

“…We then introduced nematodes in the centre of the plates and allowed them to move freely. For reasons of comparability with previous work (Riemann & Schrage 1978, Riemann & Helmke 2002, we chose a species of the omnivorous/facultatively predatory nematode genus Adoncholaimus, i.e. A. fuscus, for our experiments.…”

“…Riemann & Schrage (1978) also observed prominent microbial growth on the tracks of marine nematodes and argued that (1) the mucus tracks provide bacteria with optimal growth conditions, and (2) micro-organisms trapped in the mucus serve as food for the nematodes; this is commonly referred to as the mucus-trap hypothesis. Recently, the functional implications of this phenomenon have been re-interpreted against the background of an extensive historical treatment of relevant observations (Riemann & Helmke 2002), but the general fact that nematode tracks -at least in artificial substrates -tend to become heavily colonised with micro-organisms remains.…”