Animal Feed Science and Technology 121 (2005) 191–204 Enrichment, isolation and characterisation of ruminal bacteria that degrade non-protein amino acids from the tropical legume Acacia angustissima C.S. McSweeney a,∗ , L.L. Blackall b , E. Collins b , L.L. Conlan a , R.I. Webb b,c , S.E. Denman a , D.O. Krause a a CSIRO Livestock Industries, Queensland Bioscience Precinct, 306 Carmody Road, St. Lucia, 4067 Qld., Australia b School of Molecular and Microbial Sciences, University of Queensland, St. Lucia, 4072 Qld., Australia c Centre for Microscopy and Microanalysis, University of Queensland, St. Lucia, 4072 Qld., Australia Abstract Acacia angustissima has been proposed as a protein supplement in countries where low quality forages predominate. A number of non-protein amino acids have been identified in the leaves of A. angustissima and these have been linked to toxicity in ruminants. The non-protein amino acid 4-n- acetyl-2,4-diaminobutyric acid (ADAB) has been shown to be the major amino acid in the leaves of A. angustissima. The current study aimed to identify micro-organisms from the rumen envi- ronment capable of degrading ADAB by using a defined rumen-simulating media with an amino acid extract from A. angustissima. A mixed enrichment culture was obtained that exhibited substan- tial ADAB-degrading ability. Attempts to isolate an ADAB-degrading micro-organism were carried out, however no isolates were able to degrade ADAB in pure culture. This enrichment culture was also able to degrade the non-protein amino acids diaminobutyric acid (DABA) and diaminopropi- onic acid (DAPA) which have structural similarities to ADAB. Two isolates were obtained which could degrade DAPA. One isolate is a novel Gram-positive rod (strain LPLR3) which belongs to the Firmicutes and is not closely related to any previously isolated bacterium. The other isolate is strain LPSR1 which belongs to the Gammaproteobacteria and is closely related (99.93% similar) to Klebsiella pneumoniae subsp. ozaenae. The studies demonstrate that the rumen is a potential rich ∗ Corresponding author. Tel.: +61 7 3214 2665; fax: +61 7 3214 2900. E-mail address: chris.mcsweeney@csiro.au (C.S. McSweeney). 0377-8401/$ – see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.anifeedsci.2005.02.018