Determination of optimum temperature and pH for lignocellulosic materials-degrading bacteria isolated from termite gut and their effect on the digestibility and in vitro fermentation parameters of some agricultural by-products

There is a shortage of animal feed and water resources in several developing countries. Thus, proper use of agro industrial by products is a useful means to overcome this problem. Agricultural by products can use as animal feeds, but because of high lignin and low protein content, their digestibility and palatability is low. Several processing method has been used to improving nutritive value of such materials (Rahal et al. 1997 and Fazaeli et al. 2004). Recently, biological delignification of lignocellulosic material has been considered as an alternative approach (Fazaeli et al. 2004). Termites gut contains different kinds of lignocellulose degrading microbes, which the possibility of their use in improving the nutritive value of agricultural by-products is a major step in compensation of animal feed shortage.
Material and The present study was conducted to determine the optimum temperature and pH for growth of symbiont bacteria degrading lignocellulosic material isolated from termite gut, and to investigate their effects on the digestibility and in vitro fermentation parameters of wheat straw (WS) and date leaf (DL). For this purpose, three bacteria including Bacillus licheniformis, Ochrobactrum intermedium and Microbacterium paludicola were used, which isolated by culture of termite guts contents in mediums containing different types of lignin and lignocellulosic materials. Sterile basal media was used as a medium for isolation process and contained the following ingredients per litre: 7.0 g K2HPO4, 3.0 g KH2PO4, 1.0 g (NH4)2SO4, 0.1 g MgSO4·7H2O (Borji 2003). Growth curves of isolated bacteria for optimum temperature and pH were obtained using nutrient broth medium. Three temperatures of 30, 37 and 40 oC and four pH of 5, 6, 7 and 8 were evaluated. After that, WS and DL were processed with these isolates in media 9 (M9) medium with following composition (per litre): 6.2 g Na2HPO4, 3.0 g KH2PO4, 0.5 g NaCl, 1.0 g NH4Cl (Kato et al. 1998). After processing, residues were collected, dried and used for in vitro gas production experiment according to Makkar (2010). For this purpose, rumen liquor was collected from two ruminally fistulated cows. Animals were maintained on a 60% hay and 40% concentrate diet according to their requirements for two weeks. Rumen contents were collected from the ventral sac of rumen before morning feeding. A completely randomized design was used to determine the optimum temperature and pH for bacterial growth as well as effects of different bacteria on in vitro gas production and fermentation parameters of treated substrates. Data were analyzed by General Linear Model (GLM) procedures of SAS (SAS Institute, 2001),
All of isolates were capable of grow at all of examined temperatures (i.e., 30, 37 and 40 oC). The optimum growth of B. licheniformis occurred at 40 oC, but the optimum growth of O. intermedium and M. paludicola was observed at 37 oC. All of isolates grew at different pH ranges (i.e., 5, 6, 7 and 8) and their optimum growth was observed at neutral pH of 7.0. At this neutral pH, highest growth for B. licheniformis, O. intermedium and M. paludicola was obtainedafter 30, 34 and 36 h of incubation, respectively. After processing, in both WS and DL, highest and lowest gas production and organic matter (OM) digestibility were observed by B. licheniformis and control treatment, respectively (P Results of present study showed that optimum growth for Ochrobactrum intermedium and Microbacterium paludicola isolated from termite gut was observed at 37 oC while it was 40 oC for Bacillus licheniformis. Optimum pH for growth of all of isolates was 7. Processing wheat straw and date leaf with bacteria, especially B. licheniformis improved rumen fermentation parameters in vitro. Research for upgrading the nutritive value of by products with ligninolytic bacteria isolated from termite gut is in infancy. Thus, further works in this field of study is needed.