Isolation and characterization of a novel 2-methyl-4-chlorophenoxyacetic acid-degrading Enterobacter sp. strain SE08.

A bacterial strain (SE08) capable of utilizing 2-methyl-4-chlorophenoxy acetic acid (MCPA) as the sole carbon and energy source for growth was isolated by continuous enrichment culturing in minimal salt medium (MSM) from a long term MCPA exposed soil. This bacterial strain was identified as Enterobacter sp. based on morphological, physiological and biochemical tests, as well as 16S rRNA sequence analysis. Its ability to degrade MCPA was determined using high performance liquid chromatography. The strain SE08 can tolerate unusually high MCPA concentrations (125-2000mg/L). The influences of culturing factors (initial concentration, pH, and temperature) on the bacterial growth and substrate degradation were studied. The results showed that the optimal MCPA degradation occurred at an MCPA concentration of 500mg/L, 30°C and pH 6.0. Under these conditions, 68.5 percent of MCPA in MSM was degraded by SE08, and the OD600nm reached 0.64 after culturing for 72h. The degradation of MCPA could be enhanced by addition of both carbon and nitrogen sources. At an initial MCPA concentration of 500mg/L, when 5g/L glucose and 2.5g/L yeast extract were added into the MSM media, the MCPA degradation was significantly increased to 83.8 percent, and OD600nm was increased to 1.09 after incubation at 30°C and pH 6.0 for 72h. This is the first study showing that an Enterobacter sp. strain is capable of degrading MCPA, which might provide a new approach for the remediation of MCPA contaminated soil and contribute to the limited knowledge about the function of Enterobacter species.

[Regional characteristics of sulfur contents in flue-cured tobacco in Hunan Province and their influence to smoking quality].

A total of 559 flue-cured tobacco samples with 3 grades (B2F, C3F and X2F) were collected from the main tobacco-growing areas in Hunan Province, and their sulfur contents were determined to study the regional characteristics of the sulfur contents and their quantitative correlations with the evaluation indices of smoking quality. The results showed that the sulfur content in the flue-cured tobacco was 0.100%-2.106% , with a mean of 0.884%. The samples with sulfur content above 0.7% accounted for 71.56% of the total. The sulfur content decreased gradually from the high sulfur content area of Central Hunan to South Hunan and Northwest Hunan. With increasing sulfur content in tobacco leaf, the aroma quality, aftertaste, combustibility and ash color went to bad, offensive odor and irritation property increased, and aroma taste, eat-taste and total smoking quality score fell down. Under the influence of applying larger amount sulfate potassium and of sulfur-type acid precipitation, the sulfur content in tobacco leaf was somewhat higher in partial areas of Hunan Province, and gave negative impact on tobacco quality, being one of key factors limiting the improvement of tobacco quality and ought to be attached enough importance in tobacco production.