A novel Clostridium tyrobutyricum strain RPT-4213 was found producing butyrate under strict anaerobic conditions. This strain produced 9.47 g L-1 butyric acid from MRS media (0.48 g/g glucose). RPT-4213 was also used to ferment dilute acid pretreated hydrolysates including wheat straw (WSH), corn fiber (CFH), corn stover (CSH), rice hull (RHH), and switchgrass (SGH). Results indicated that 50% WSH with a Clostridia medium (Ct) produced the most butyric acid (8.06 g L-1, 0.46 g/g glucose), followed by 50% SGH with Ct (6.01 g L-1, 0.44 g/g glucose), however, 50% CSH Ct showed growth inhibition. RPT-4213 was then used in pH-controlled bioreactor fermentations using 60% WSH and SGH, with a dilute (0.5 x) Ct medium, resulting 9.87 g L-1 butyric acid in WSH (yield 0.44 g/g) and 7.05 g L-1 butyric acid in SGH (yield 0.42 g/g). The titer and productivity could be improved through process engineering. Published by Elsevier Ltd.