Presence of Culturable Bacteria in Cocoons of the Earthworm Eisenia fetida

Abstract

Viable bacteria were found to coexist with developing embryos in egg capsules (cocoons) of the earthworm Eiseniafetida. Earthworms were reared under standardized conditions, and bacterial densities were measured in distinct batches of cocoons collected weekly for 10 weeks. Cocoons weighing 12 mg contained a mean viable bacterial population of approximately 108 CFU/g of cocoons. No difference was found in viable counts obtained from cocoons incubated at 15°C and cocoons incubated at 24°C. Viable bacterial numbers increased with cocoon age, while acridine orange direct counts of microbial cells were stable at approximately 109 cells per g of cocoons. Bacteria isolated from cocoons were used to develop antisera in rabbits for the production of strain-specific fluorescent antibodies. Fluorescent antibody and selective plating techniques were used to monitor populations of these bacteria in earthworm bedding and to determine whether cocoons acquire bacteria from the environment in which they are formed. Cocoon isolates were readily recovered from cocoons formed in inoculated bedding at densities of 108 CFU/g of cocoons. Bradyrhizobiumjaponicum USDA 110 and UMR 161 added to bedding were also recovered from cocoons, but at lower densities than cocoon isolates. Escherichia coli K-12(pJP4) inoculum was recovered from bedding but not from cocoons. The bacterial complement ofEiseniafetida cocoons is affected by inoculation of selected bacterial isolates in the worm growth environment.

Earthworm Egg Capsules as Vectors for the Environmental Introduction of Biodegradative Bacteria

“…This age was chosen since viability can easily be assessed by observing either embryo movement or blood circulation. In addition, studies have shown bacterial numbers to increase with increasing cocoon age (8,32). Therefore, an age range of 12 to 19 days provides for an accurate prediction of the bacterial numbers which will be released upon cocoon hatching, which usually begins around an age of 24 days but may take as long as 45 days for complete development.…”

“…Attempts to identify several of the morphologically diverse cocoon isolates were inconclusive. In addition, Zachmann and Molina (32) determined that cocoons may acquire bacteria from the environment from which they are formed; however, the location and function of the bacteria within the cocoon were not ad-dressed in that study. Recently, Daane et al (8), using scanning electron microscopy, determined the location of bacteria within the developing earthworm cocoon.…”

“…Several studies have shown that microorganisms are associated with earthworm egg capsules (cocoons) (8,18,32). Morgan and Burrows (18) reported that the internal fluid of Eisenia fetida cocoons contained bacteria of the genera Nocardia, Pseudomonas, and Alcaligenes.…”

“…Morgan and Burrows (18) reported that the internal fluid of Eisenia fetida cocoons contained bacteria of the genera Nocardia, Pseudomonas, and Alcaligenes. Zachmann and Molina (32) were the first to quantify the bacteria present in egg capsules of E. fetida, with up to 10 8 CFU g Ϫ1 of cocoon. Attempts to identify several of the morphologically diverse cocoon isolates were inconclusive.…”

Pontoscolex corethrurus:a Homeless Invasive Tropical Earthworm?

“…The hologenome (sum of the genetic information of the host and its microorganisms) theory of evolution is based on four generalization: a) all animals and plants establish symbiosis with microorganims; b) microorganisms can be transmitted between generations with fidelity; c) symbiosis affects the fitness of holobionts in their environment; d) genetic variation in holobionts can be enhanced by incorporating different symbiont populations and can change rapidly under enviromental stress (Zilber-Rosenberg and Rosenberg 2008). Earthworms harbor symbiotic microbiomes that are essential for their life history in the gut, nephridia (excretory organs), and cocoons, but the evolutionary relationship in tropical species such as P. corethrurus is poorly understood(Zachmann and Molina 1993;Schramm et al 2003;Daane et al 1999;Lund et al 2010a and2010b;Aira et al 2018); for instance, the microbiome is known to improve the nutritional status of low-quality diets(Lund et al 2010b;Aira et al 2018). Our findings showed that P. corethrurus and B. pearsei differ in their diet preference (M. pruriens, corn stubble, and 13 control), i.e., the invasive species displayed a faster growth than the native species when nutritional quality improved.…”