Morpho-Histology of Gut and Microbiological Study on Gut Content of Earthworms of Rajshahi University Campus

Abstract

Earthworm plays an important role on economy and society of Bangladesh which is based on agriculture. A fertile and productive soil is the fundamental resource for sustainable Agriculture. Earthworm can play a variety of important roles in fertility and productivity of soil by providing shelter to the beneficial microbes in their gut and by activating soil microbial activity through the excretion and casting. Many microorganisms in the soil remain in the dormant stage, awaiting suitable habitat for the vigorous multiplication. Earthworm gut is suitable habitat for many microorganisms, but not for all. Many microorganisms may be digested in gut. Therefore, present investigation was done to find out the morpho-histological and microbiological variation in gut of different earthworm species. Then, investigation was done to ascertain the correlation between morpho-histological variation and microbial variation of gut of different earthworm species. Rajshahi University campus was the study area of the present research work. Three types of habituates i.e., shady land, crop land and drainage of residential hall were selected for study from September, 2004 to August, 2005. The fortnightly sampling dates were fixed on 14th day for first sampling and 28th day for 2nd sampling each month. Quadrate sampling and Hand sorting methods were used to collect earthworm. Collected earthworms were identified with an identification key. Data on weather were collected from Regional Weather Office of Rajshahi. For morphological study, earthworms were dissected and cleaned to separate the gut. Permanent slides of gizzard, stomach and intestine of the gut were prepared and then observed by advanced biological microscope for histological study. Bacterial load of gut of earthworm was studied by serial dilution method and spread plate technique on nutrient agar plate. Finally, pure culture of bacteria isolated from the different parts of gut of earthworms were tested for Gram character, morphology, motility, catalase and oxidase reactions, citrate utilization and coagulase test. The isolates were then identified with Bergey's manual of systematic bacteriology. Six species of earthworm i.e., Metaphire posthuma, Eutyphoeus orientalist, Eutyphoeus Nicholson, Eutyphoeus incommodious, Lampito Mauritia and Drawida lime/la were identified from three studied habitats. Earthworm diversity was present in the studied habitats. The number of earthworms also varied with month. In most cases, higher number of earthworms was recorded on July, August and September. On the other hand, lower number of earthworms was recorded from November to April. Morphological study of gut of earthworm revealed that number, length and position of different parts of gut of all studied earthworm species were not same. Result of histological study showed that same layers of muscle and cuticle were presence in gut of all studied species of earthworm, but some species ways variation were found in the width of the different layers of the gut. Result of bacterial load study showed that bacterial load of gut varies with part of the gut, species of earthworm and season or month of the year. But species ways variation of bacterial load was not statistically significant. Analysis of correlation indicates that bacterial load of one part gut is correlated with that of other parts of gut and also with the components of weather. The highest bacterial load of gizzard was recorded in D. lime/la on September while the lowest load was recorded in E. Nicholson on January. Bacterial load of stomach of E. oriental it was higher than that of the other species from January to May, but that of E. Nicholson was higher than that of the other species from June to December. Bacterial load of stomach of D. lime/la was lower than that of the other species from December to July. But miscellaneous result was found on lower bacterial load from August to November. The highest bacterial load of intestine was recorded in E. Nicholson on September while the lowest load was recorded in E. incommodious on December. Five genera of bacteria were identified from six species of earthworm. These were Bacillus, Pseudomonas, Klebsiella, Streptococcus and Acinetobacter. No remarkable variation of bacterial fauna was found in studied species of earthworm. In other ward, these five types of bacteria were found in all studied species of earthworm. It can be concluded that there is morpho-histological variation in gut of different earthworm species. But morphological variation was more prominent than the histological variation of gut of earthworm. One other hand, insignificant species ways variation of bacterial load and uniform types of gut bacteria reveal that there is no species-specific bacterial profile for gut of different earthworm. Therefore, form the data of this study it is not possible to establish a method for identification of an earthworm species depending on their bacterial profile of gut.