Three xylanase producing alkaliphilic bacterial strains designated AR-009, AR-135 andrnAR-22-1, were isolated from Lake Arenguadie, an alkaline soda lake in Ethiopia. AR-rn009 and AR-135 were identified as strains of the genus Bacillus and Micrococcus,rnrespectively, while AR-22-1 remains unidentified. The enzyme from all the 3 strainsrnwere purified following standard protein purification procedures, and the molecularrnweight of each enzyme was estimated using SDS-PAGE.rnTwo xylanases designated as xylA and xylB, having molecular weights of 23 and 48rnkD, respectively, were purified from the cell free culture supernatant of Bacillus sp.rnAR-009. XylA was optimally active at pH 9 while xylB showed optimum activity inrnthe pH range of 9 to 10 and stable from pH 5 to 11. The optimum temperature for thernactivity of xylA was 70Â°C at pH 8 and 60Â°C at pH 9. On the other hand xylB wasrnoptiImilly active at 70Â°C at pH 8 and 75Â°C at pH 9. Both enzymes showed goodrnstability at 60Â°C and at a pH of 8 and 9.rnAR-135 xylanase was optimally active at 55Â°C and a pH of 7.5 - 9.0. Over 60% ofrnthe maximum activity was displayed at pH 11. Its thermal stability above 40Â°C wasrnvery low. The optimum temperature and pH for the activity of AR-22-1 xylanase wasrn70Â°C and 8.0 to 9.5, respectively. The enzyme was stable in a broad pH range andrnshowed good stability up to 60Â°C at pH 8 and 9rnAgar immobilized cells of Bacillus sp. AR-009 were used for xylanase production withrna view of finding cheap ways of enzyme production. In a batch culture maximumrnenzyme production was observed after 48 h and remained high up to 72 h. In repeatedrnbatch cultivation immobilized cells produced appreciable level of xylanase activity in 7rnconsecutive batches with out any significant decline in productivity. For continuousrnxylanase production immobilized cells were packed in a jacketed glass coluIlUl andrnsterile medium was continuously pumped. A stable continuous production of xylanasernwas observed over a period of one month. The volumetric productivity of therncontinuous culture was 17 fold higher than the batch culture using free cells.rnAnother method of enzyme production investigated was the use of solid staternfennentation. Bacillus sp. AR-009 produced high level of xylanase activity whenrngrown using solid state fermentation (SSF) with wheat bran serving as a substrate.rnXylanase production was highest at a wheat bran to moisture ratio of between 1:0.5 torn1: 1.5 and a Na2COJ concentration of 10% (w/w). No significant effect was observedrnon xylanase production when wheat bran is supplemented with peptone, try one, andrnyeast extract, thus avoiding the need to supplement wheat bran with expensive media.rnThe ability of the organism to produce high titre xylanase activity at alkaline pH andrnlower wheat bran to moisture ratio could have a potential advantage in minimising thernrisk of contamination. In addition, because the enzyme can be extracted usingrnminimum volume of liquid, the cost of down stream processing during productrnupgrading and the cost of waste treatment steps can be greatly reduced. The use of SSFrnfor the production of xylanase by Bacillus sp. AR-009 could therefore lead tornsubstantial reduction in the over all cost of enzyme production.