Abstract
Large amounts of straw accumulate as a by-product of paddy cultivation. However, proper management of bulky straw has
become a concern worldwide. We therefore explored potential bacterial isolate(s) for rice straw bioconversion. A study
comprising several experiments was conducted at Composting Unit and Laboratory of Food Crops of Universiti Putra Malaysia
under controlled condition. In total, 33 bacterial isolates were obtained from various sources of decomposed rice straw, such
as composts or soil. The results showed that isolates UPMB7, UPMB8, UPMB10, UPMB17, and UPMB25, tested on ricestraw-powder amended media, exhibited optimum lignocellulolytic activities. UPMB7 and UPMB25 were further screened for
rice straw bioconversion. Finally, the most optimal lignocellulolytic bacterial isolate, UPMB25, was identified as Bacillus
subtilis using 16S rRNA sequencing and tested for in vivo rice straw bioconversion. UPMB 25 (B. subtilis) decomposed rice
straw at a significantly higher rate than the control, with respect to both in-vitro and in-vivo bioconversion. At day 7, UPMB
25-inoculated compost showed optimum lignin peroxidase (LiP) activity of 6.06 μmol veratraldehyde•min-1
•g-1
, endoglucanase
activity of 7.37 CMC•g-1
, exoglucanase activity of 3.79 FPA•g-1
, and fluorescein diacetate (FDA) hydrolysis activity of 1428.8
µg fluorescein•min-30•g-1
at day 14. After 4 weeks, the germination index of tomato seeds was found to be 80%, indicating the
potential of UPMB25, B. subtilis, to be used as an efficient lignocellulolytic bacterium for large scale composting of rice straw.
