N-174. Investigating the Microbial Communities Associated with Xylophagy in the Gastrointestinal Tract of Panaque nigrolineatus

D. Smoot¹, N. M. Mohamed², J. A. Nelson¹, H. J. Schreier², J. E. M. Watts¹;
¹Towson Univ., Towson, MD, ²Univ. of Maryland, Baltimore, MD.

Panaque nigrolineatus is a species of armored catfish found in Brazil and other tropical areas that is capable of survival using a xylophagous lifestyle. While little is known about the nature of xylophagy, the ability to thrive on a wood-only diet, it is likely that microbial communities associated with the intestinal tract provide the mechanisms for cellulose decomposition and nitrogen fixation. Thus, an understanding of microbial communities associated with xylophagy may yield novel metabolic pathways for cellulose degradation and nitrogen fixation with important applied implications. The microbial communities present in P. nigrolineatus was examined using molecular tools. DNA extractions were performed on select regions of the GI tract including the foregut, midgut, hindgut, and auxillary lobe and microbial DNA was subjected to universal 16S rRNA PCR amplification and examined by denaturing gradient gel electrophoresis (DGGE). Rapid fingerprints were obtained from the different regions of the GI tract, allowing comparison of each community. Microbial species diversity appeared to be highest in the hindgut region of the GI tract, and distinct differences could be observed in each of the other regions. An analysis of clone libraries of the 16S rRNA gene obtained from each region revealed the presence of a number of cellulolytic species with high sequence similarity to Clostridium cellulovorans, Clostridium cellulose, Streptomyces cellulosae and Streptomyces cellostaticus, which are likely to play a role in xylophagy. In addition, the use of degenerate nifH32/nifH623 and nifH1/nifH2 PCR primer sets applied to total intestinal DNA preparations resulted in the amplification of internal nitrogenase nifH gene fragments, which were cloned and examined. At least three nifH groups were identified, two having high sequence similarity to Sinorhizobium sp. and Ideonella sp. of the alpha-proteobacteria and a third that was highly similar to Azotobacter sp. of the gamma-proteobacteria, indicating a role for nitrogen-fixing bacteria in xylophagous lifestyle of these fish.