Mal-Nam Kim

A thermophilic bacterium capable of low-molecular-weight polyethylene (LMWPE) degradation was isolated from a compost sample, and was identified as Chelatococcus sp. E1, through sequencing of the 16S rRNA gene. LMWPE was prepared by thermal degradation of commercial PE in a strict nitrogen atmosphere. LMWPE with a weight-average-molecular-weight (Mw) in the range of 1,700–23,700 was noticeably mineralized into CO₂ by the bacterium. The biodegradability of LMWPE decreased as the Mw increased. The low molecular weight fraction of LMWPE decreased significantly as a result of the degradation process, and thereby both the number-average-molecular-weight and Mw increased after biodegradation. The polydispersity of LMWPE was either narrowed or widened, depending on the initial Mw of LMWPE, due to the preferential elimination of the low molecular weight fraction, in comparison to the high molecular weight portion. LMWPE free from an extremely low molecular weight fraction was also mineralized by the strain at a remarkable rate, and FTIR peaks assignable to C–O stretching appeared as a result of microbial action. The FTIR peaks corresponding to alkenes also became more intense, indicating that dehydrogenations occurred concomitantly with microbial induced oxidation.

Preparation and Applicability of Vinyl Alcohol Group Containing Polymer/MWNT Nanocomposite Using a Simple Saponification Method | InTechOpen, Published on: 2011-08-17. Authors: Eun-Ju Lee, Jin-San Yoon, Mal-Nam Kim, et

A total of 1921 Escherichia coli isolated from healthy animals (501 from cattle, 832 from pigs, and 588 from chickens) and 237 isolates from diseased pigs were tested to determine the prevalence of apramycin and gentamicin resistance in Korea during 2004–2007. Apramycin/gentamicin resistances observed in healthy cattle, pigs, and chicken were 0.2%/0.6%, 11.2%/13.6%, and 0.5%/18.2%, respectively. Gentamicin/apramycin resistance was much higher in E. coli isolated from diseased pigs (71/237, 30.0%) than in those from healthy pigs (93/832, 11.2%). The aminoglycoside resistance gene content of all apramycin-gentamicin-resistant E. coli isolates (n = 164) was determined by polymerase chain reaction. Of seven different types of aminoglycoside resistance genes tested, five kinds were detected in the 164 isolates: aac(3)-IV, aac(3)-II, aac(3)-III, ant(2′′)-I, and armA. All apramycin-resistant E. coli contained the aac(3)-IV gene. About half of the resistant isolates carried only the aac(3)-IV gene and the other half carried other genes in addition to aac(3)-IV. The results of the present study suggest that humans are at risk of gentamicin resistance from apramycin use in animals.

A Gram negative, rod‐shaped mesophilic bacterium active for poly(L‐lactide) (PLA) degradation was isolated through the enrichment culture and clear‐zone method. The isolated strain was identified to be Bordetella petrii PLA‐3 on the basis of 16S rDNA gene sequence analysis. B. petrii PLA‐3 was active not only for the degradation of low‐molecular‐weight PLA but also for the degradation of high‐molecular‐weight PLA. The strain seemed to attack the crystalline part of PLA as well as the amorphous region. The PLA film incubated in compost inoculated with the isolated strain lost its weight more notably and exhibited a lower molecular weight than that incubated in the sterilized compost without living microorganisms. Moreover, the profile of the cumulative amount of CO₂ after 20 days of burial in the sterilized compost and subsequent inoculation of the isolated strain into compost was nearly the same as that of CO₂ evolved from PLA buried in compost with the isolated strain at the very beginning when the time was shifted by 20 days. This indicated that not only the abiotic hydrolysis but also the microbial enzymes of the strain contributed to the initial chain cleavage of PLA molecules and resolved the doubt that PLA molecules should be initially cleaved into very low‐molecular‐weight substances by abiotic hydrolysis to be subsequently absorbed into and biodegraded by microorganisms. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Polymerase chain reactions (PCR) were performed to accomplish quick and accurate detection of Vibrio species. The primers prepared with 16S-23S rDNA intergenic spacer (IGS) region exhibited an excellent species-specificity for Vibrio sp and detected Vibrio sp more successfully than the conventional culture method. Multiplex PCR was also fruitful not only forthe identification of the 5 standard Vibrio sp simultaneously but also for the detection of Vibrio spin the samples collected from the natural environment.

A new strain exhibiting poly(L‐lactic acid) (PLLA)‐degrading activity was isolated from the compost loaded with low‐molecular weight PLLA. The strain was rod‐shaped gram positive bacterium and was identified to be Bacillus licheniformis by the 16S rDNA sequence analysis. It degraded not only low‐molecular weight PLLA but also other PLLAs having higher molecular weight. The lower the molecular weight of PLLA, the faster the biodegradation rate. And thereby 45% and 81% of PLLAs with weight average molecular weight of 256,000 and 5,000, respectively, were metabolized into CO₂ after 40 days of biodegradation at 58°C in the sterilized compost inoculated with the bacterium. According to the 16S rDNA sequence analysis, B. licheniformis PLLA‐2 belonged to Bacillus spp. phylogenetically. However, there existed almost no phylogenetic relationship between B. licheniformis PLLA‐2 and the previously reported PLLA‐degrading strains. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008