عنوان مقاله [English]
Introduction: There is a shortage of animal feed and water resources in many countries around the world. Numerous agricultural by-products are produced annually in all countries, thus their proper use is often a useful means of overcoming this problem. Large proportions of these materials are important feeds for ruminant animals and can be used as a potentially significant source of energy. However, the use of these materials as ruminant feed is limited because of their complex structure, low protein and high lignin content. Different physical and chemical methods have been used to increase the nutritive value of such by-products. Although these methods have advantages, they are costly, relatively ineffective and environmentally unfriendly and require the application of technology. Recently, biological processing of lignocellulosic biomass has been considered as an alternative approach. Three groups of organisms are able to biodegrade lignin namely, white rot fungi, some soil microbes and termites. In recent years, increased attention has been given to the role of bacteria in lignin degradation in agricultural by-products. Insects that utilize wood as a food source are beetles, cockroaches and termites. Termites are especially well known for their ability to break down the lignin barrier and digest carbohydrate polymers. Researcher has isolated 3 bacterial species from the Anacanthotermes vagans termite gut, including Bacillus sp., Enterobacter sp., and Ochrobacterium sp. These bacteria could grow on different media containing lignin and lignocellulosic materials prepared from water extracted wheat straw and sawdust as a sole source of carbon and energy. In another study three bacteria include Bacillus licheniformis, Ochrobactrum intermedium and Microbacterium paludicola were isolated by culturing the gut contents of the termite Microcerotermes diversus on different media containing lignin and lignocellulose as a sole source of carbon and energy. Isolates could partially change the chemical composition of the wheat straw and date leaves, while nutrient digestibility increased. However, Zeuzera pyrina L. is also another insect which degrade lignocellulose. Larval tunnels in the wood and girdling burrows under the bark are visible at the ends of broken stems. Numerous partly broken branches with dead brown foliage hanging in tree crowns are characteristic of heavy infestations. In our knowledge, little work has been done on the isolation of lignin and lignocellulose-degrading bacteria from gut of Zeuzera pyrina. Therefore, the aim of the present study was to isolate and identify symbiotic lignocellulosic degrading bacteria from the Zeuzera pyrina L. gut, and to investigate their effects on the nutritive value of wheat straw and sugarcane tops as ruminant feed.
Material and Methods: This experiment was conducted in animal house and laboratories of Lorestan University. Two Lori cows (about five years old) with permanent rumen fistula were used as rumen liquor donor in present study. A two-week diet adaptation period was followed by collection of the rumen contents from each cow before the morning feeding. The aim of the present study was investigate nutritive value of wheat straw (WS) and sugarcane tops (ST) treated with bacteria isolated from gut of Zeuzera pyrina. For this purpose, first, based on 16S rDNA sequence analysis, 3 bacteria including Enterobacter cloacae, Staphylococcus sciuri and Brevibacterium sp., with lignin and lignocellulose-degrading potential were isolated from gut of this insect. Thereafter, each of WS or ST were processed with these isolated individually or with mix of them (totally 4 treatment group for each substrate) in liquid medium. Chemical composition, in vitro gas production (IVGP) and fermentation parameters of these two processed by-product were determined compared to control treatment.
Results and Discussion: Results showed that highest amount of dry matter (DM) loss, crude protein, in vitro DM digestibility and metabolizable energy was observed in both substrates (i.e., WS and ST) treated with bacterial mixture of Zeuzera pyrina compared to control. Highest volume of IVGP and potential of GP (b) were observed after processing by bacterial mixture of Zeuzera pyrina compared to control treatment (P>0.05). Highest volatile fatty acid (VFA) concentration, acetate, acetate to propionate ratio and ammonia-N concentration were observed in substrates inoculated with bacterial mixture in comparison with control treatment (P<0.05).
Conclusion: In this experiment, we isolated three bacteria including Enterobacter cloacae, Staphylococcus sciuri and Brevibacterium sp., with lignin and lignocellulose-degrading potential from the gut of Zeuzera pyrina. Processing WS and ST with these individual bacteria, especially media containing their mixture improved their nutritive value as ruminant feed via increasing DM digestibility and VFA production.
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