Origins and fate of fungi and bacteria in the gut of Lumbricus terrestris L. studied by image analysis

Abstract

The effect of the passage through the gut of the earthworm Lumbricus terrestris L. on fungi and bacteria ingested with decomposing leaves of Taraxacum officinale and with soil was quantified using image analysis tools. Both leaf and soil material were labeled with fluorescent latex microbeads to allow a quantification of the food sources in the fore-, mid-, and hindgut of the earthworms. The content of leaf material in the gut varied in a range between 4 and 59% of the total gut content in different earthworms and the different parts of the intestine of individual animals. Filamentous fungi in the gut compartments were found to originate mainly from leaf material (7700 þ 1800 Wg (g leaf (dry wt.)) 3I ), however, the major part was disrupted before arriving in the intestine. Remaining hyphae in the foregut with a biomass of up to 900 þ 150 Wg (g gut content (dry wt.)) 3I were completely digested during passage through the earthworm gut. Spores of fungi were not detected in our studies. Bacterial cell numbers in the gut compartments ranged from 63 þ 5U10V to 327 þ 16U10 V (g gut content (dry wt.)) 3I and were significantly higher than the numbers found in the soil (50 þ 1U10V cells (g soil (dry wt.)) 3I ). Cell numbers usually increased from fore-to hindgut. This increase was not correlated to contents of organic material and only partially due to a multiplication of bacterial cells. Numbers of dividing cells accounted in total for approximately 12% of all bacteria, increasing significantly from fore-to hindgut, counts were from 10 þ 1U10V to 25 þ 2U10 V (g gut content (dry wt.)) 3I , respectively. Average cell volumes of bacteria calculated from cell size distributions in leaf and soil material differed significantly, being 0.197 and 0.063 Wm Q , respectively. In the gut compartments, average cell volumes ranged from 0.043 to 0.070 Wm Q , which may indicate the disruption of large cells originating from the leaves before arriving in the foregut. z

The Serendipitous Value of Soil Fauna in Ecosystem Functioning: The Unexplained Explained

“…Both mesofauna (microarthropods) and macrofauna (earthworms) are known to carry cells, spores and mycelium attached to their bodies and in their guts and then released out again via egestion in their feces. While phoresy will help transported microorganisms in colonizing new areas, gut passage could result in either activation or destruction of the microbial cells (e.g., Schoënholzer et al, 1999;Renker et al, 2005;Buse et al, 2014). In other cases, although spore/propagule viability is retained, germination might be delayed (Talbot, 1952).…”

The predatory soil flagellate Heteromita globosa stimulates toluene biodegradation by a Pseudomonas sp.

“…Hence, numbers of bacteria required to produce one £agellate division were calculated from 1/Y cell . The carbon conversion e¤ciency (CCE) for £agel-lates was estimated using published data [3] Biovolumes of bacteria and £agellates were measured using a method described previously [16]. Biovolumes of bacteria measured using DAPI were 2.2 times smaller than their bright ¢eld equivalents and were corrected accordingly (Scho « nholzer, personal communication).…”