Abstract
The growing demand for wood has resulted in large volumes of wood wastes that are daily released to the soil from the activities of sawmills in South-Western Nigeria. In an attempt to setup a bioremediation model for sawdust, this study therefore aimed at evaluating microbial diversity, and the level of digestive enzymes in the gut of earthworms (Eudrilus eugeniae, Libyodrilus violaceous and Hyperiodrilus africanus) of sawmill origin. Four major sawmills located in Abeokuta (7°9'12" N- 3°19'35" E), namely Lafenwa, Sapon, Isale-Ake and Kotopo sawmills were used for this study. The arboretum of the Federal University of Agriculture, Abeokuta was used as control. Gut microbial analysis was carried out using the pour-plate method while digestive enzyme activities in the earthworm guts were done by the spectrophotometric method. Higher microbial counts (28.5 ± 0.1 x 10(3)-97.0 ± 0.1 x 10(3) cfu for bacteria and 7.0 ± 0.1x 10(3)-96.0 ± 0.1 x 10(3) cfu for fungi) and microbial diversity were recorded in the gut of earthworms of the sawmill locations than those of the control site (17.5 ± 0.1 x10(3) cfu for bacteria and 4.5 ± 0.1 x 10(3) cfu for fungi). Streptococcus mutans and Proteus spp. were common in the gut of E. eugeniae, and L. violaceous from the study sawmills, while Streptococcus mutans were also identified in H. africanus, but absent in the gut of E. eugeniae from the control site. Cellulase (48.67 ± 0.02 mg/g) and lipase (1.81 ± 0.01 mg/g) activities were significantly higher (p < 0.05) in the gut of earthworms from the control site than those of the study sawmills. Furthermore, amylase (α and β) activity was highest in the gut of earthworms from the sawmills. Variations observed in the gut microbial and digestive enzyme activities of earthworms from the study sawmills as compared to the control site suggests that earthworms, especially E. eugeniae, could be a better organism for use as bioremediator of wood wastes.
Highlights
Sawmilling is a major enterprise providing direct and indirect employment for thousands of people in the tropical rain forest region of Nigeria where there is abundance of trees (Ihekwaba, Nwafor, & Adienbo, 2009)
Hornor & Mitchell (1981) suggested that the ingested microbial populations play a key role in earthworm nutrition by helping in the breakdown of organic matter, the components that the earthworms cannot utilize in their natural state
Microbial Count: Microbial load count in the gut of the earthworm samples showed that the gut of E. eugeniae from sawmills had higher microbial count compared to those from the control site (Table 1)
Summary
Sawmilling is a major enterprise providing direct and indirect employment for thousands of people in the tropical rain forest region of Nigeria where there is abundance of trees (Ihekwaba, Nwafor, & Adienbo, 2009). It is well established that earthworms (Class Oligochaetae; Phylum Annelida), play important roles in the terrestrial ecosystem (Debasmita, Mishra, & Mohapatra, 2011) Some of these roles include soil aeration (Olayinka et al, 2011; Owa, Dedeke, & Yeye, 2002), humus formation (Renu, Pandey, Bisht, Kandpal, & Kausha, 2006) and organic matter recycling (Satchell, 1967). Earthworms transform organic waste constituents into more useful forms by grinding and digesting with the aid of aerobic and anaerobic microflora (Maboeta & Van Rensberg, 2003) This biological decomposition of organic matter has been described to be mediated by a variety of biochemical processes in which enzymes play a key role (Garcia, Hernandez, Costa, Ceccanti, & Ciardi, 1992; Vuorinen, 1999). Sawmills are a very common industry in the South-Western part of Nigeria These industries release high volumes of sawdust which have cellulose, hemicelluloses and lignin as its major constituent. The sawdust produced are usually spread over the sawmill soils
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