Screening Of Low Temperature Degrading Bacteria And Its Degradation Performance From Rice Straw

Rice straw is one of the world’s major lignocellulosic wastes,rich in resources and a raw material for the production of biofuels and chemicals.At present,the main treatment is to return straw to the field,which not only reduces air pollution and health hazards caused by in situ burning,but also increases straw utilization and improves soil properties.However,direct return of straw to the field without timely decomposition will aggravate the occurrence of pests and affect the growth of the next crop.Especially in northern China,where the winter is long and the temperature continues to be low,the activity of microorganisms is reduced,so that straw is not easy to degrade.Therefore,it is very critical to screen rice straw low temperature degradation bacteria to improve the rate of straw degradation under low temperature conditions.In this experiment,the following work was done to screen rice straw low temperature degrading bacteria and study its straw degradation effect.（1）The source consortium of the screened strains degraded at 20℃for 14 d with a weight loss rate of 46.65±1.33%.Four strains L1,W118,W59 and L16 with good disintegrating effect were obtained from soil of different cold habitats by screening and eliminating the strains with no straw degradation ability.Two strains W118 and L1 were cultured at 4℃,and strain W118 was obtained.The strain L1 was identified as Acinetobacter lwoffii,strain W59 was identified as Acinetobacter johnsonii and strain L16 was identified as Gemmobacter sp.by 16S r DNA sequence analysis.Combined with physiological and biochemical characteristics,strain W118 was identified as Bacillus cereus.（2）The growth characteristics of strain W118 were determined,and the results showed that the optimum growth temperature was 20℃,and the optimum growth p H was 6.5.The OD_600nm could reach 7.12±0.07 after 30 h of growth under the optimum conditions.The ligninase activity and urea amidehydrolase activity of strain W118 were measured,and the results showed that the activity of carboxymethyl cellulase was 3.16±0.02 U/m L,the activity of filter paper enzyme was 5.66±0.07 U/m L,the activity ofβ-glucosidase was 2.07±0.08U/m L,and the activity of lignin peroxidase was 0.20±0.01 U/m L.Laccase activity was 0.30±0.02 U/m L and urea amidehydrolase activity was 1.66±0.08 U/m L.（3）The activity characteristics of carboxymethyl cellulase of strain W118 were explored.The results showed that the optimum fermentation temperature was 20℃,the optimum fermentation initial p H was 7.0,the optimum reaction temperature was 30℃and the optimum reaction p H was 8.0.（4）The degradation efficiency of strain W118 was measured.And the weight loss rate of rice straw was 27.00±0.02%at the temperature of 20℃for 14 d,using 2%of the bacterial solution as inoculum.The weight loss rate of rice straw at 4℃for 14 days was 23.70±0.04%,and that at 25 days was 50.71±0.02%.（5）The straw was pretreated with sodium hydroxide/urea and electrohydrolysis.SEM,XRD and FTIR analysis showed that both pretreatments could effectively destroy the lignin structure of the rice straw and improve the crystallinity of cellulose.After pretreatment,strain W118 degraded the rice straw.After 14 d of degradation,the reducing sugar content of sodium hydroxide/urea and electrohydrolysis pretreated straw increased 3.2-fold and 1.7-fold,respectively（unpretreated rice straw 270.95±3.60 mg/g rice straw）.