• Korean Journal of Environmental Agriculture
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• v.42 no.3
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• pp.169-176
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• 2023

The emergence and spread of antibiotic-resistant bacteria have been increasing with anthropogenic contamination. Understanding the prevalence and distribution of these resistant bacteria in environments is crucial for effectively managing anthropogenic pollutants. Lake Gyeongpo in the Gangwon Province of South Korea is known for its diverse ecological features and human interactions. The lake is exposed to pollutants from nonpoint sources, including urban areas, agricultural practices, and recreational activities, which can introduce antibiotics and foster antibiotic resistance in bacteria. The present study investigates Lake Gyeongpo as a potential reservoir for antibiotic-resistant bacteria in a natural ecosystem. A total of 203 bacterial isolates were collected from six sampling locations in Lake Gyeongpo during May, July, and November 2022. Most isolates were taxonomically identified as Pseudoalteromonas, Bacillus, Shewanella, and Vibrio spp.; their abundance showed a spatiotemporal distribution. An antibiotic susceptibility test was conducted on 75 isolates using the disk diffusion method with six drugs according to the CLSI guideline; 42 isolates were resistant to one or more antibiotics. Among these, 15 isolates were identified as multidrug resistant bacteria. This finding suggests the potential anthropogenic impact on Lake Gyeongpo and provides valuable insights into the dissemination of antibiotic resistance caused by anthropogenic pollutants.

• Journal of Microbiology and Biotechnology
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• v.27 no.8
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• pp.1441-1448
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• 2017

Antibacterial compounds are widely used in the treatment of human and animal diseases. The overuse of antibiotics has led to a rapid rise in the prevalence of drug-resistant bacteria, making the development of new antibacterial compounds essential. This study focused on developing a fast and easy method for identifying marine bacteria that produce antibiotic compounds. Eight randomly selected marine target bacterial species (Agrococcus terreus, Bacillus algicola, Mesoflavibacter zeaxanthinifaciens, Pseudoalteromonas flavipulchra, P. peptidolytica, P. piscicida, P. rubra, and Zunongwangia atlantica) were tested for production of antibacterial compounds against four strains of test bacteria (B. cereus, B. subtilis, Halomonas smyrnensis, and Vibrio alginolyticus). Colony picking was used as the primary screening method. Clear zones were observed around colonies of P. flavipulchra, P. peptidolytica, P. piscicida, and P. rubra tested against B. cereus, B. subtilis, and H. smyrnensis. The efficiency of colony scraping and broth culture methods for antimicrobial compound extraction was also compared using a disk diffusion assay. P. peptidolytica, P. piscicida, and P. rubra showed antagonistic activity against H. smyrnensis, B. cereus, and B. subtilis, respectively, only in the colony scraping method. Our results show that colony picking and colony scraping are effective, quick, and easy methods of screening for antibacterial compound-producing bacteria.

• Journal of Microbiology and Biotechnology
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• v.26 no.11
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• pp.1933-1942
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• 2016

A novel ${\alpha}-glucoside$ hydrolase (named PspAG97A) from glycoside hydrolase family 97 (GH97) was cloned from the deep-sea bacterium Pseudoalteromonas sp. K8, which was screened from the sediment of Kongsfjorden. Sequence analysis showed that PspAG97A belonged to GH97, and shared 41% sequence identity with the characterized ${\alpha}-glucoside$ BtGH97a. PspAG97A possessed three key catalytically related glutamate residues. Mutation of the glutamate residues indicated that PspAG97A belonged to the inverting subfamily of GH97. PspAG97A showed significant reversibility against changes in salt concentration. It exhibited halophilic ability and improved thermostability in NaCl solution, with maximal activity at 1.0 M NaCl/KCl, and retained more than 80% activity at NaCl concentrations ranging from 0.8 to 2.0 M for over 50 h. Furthermore, PspAG97A hydrolyzed not only ${\alpha}-1,4-glucosidic$ linkage, but also ${\alpha}-1,6-$ and ${\alpha}-1,2-glucosidic$ linkages. Interestingly, PspAG97A possessed high catalytic efficiency for long-chain substrates with ${\alpha}-1,6-linkage$. These characteristics are clearly different from other known ${\alpha}-glucoside$ hydrolases in GH97, implying that PspAG97A is a unique ${\alpha}-glucoside$ hydrolase of GH97.

• Journal of Soil and Groundwater Environment
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• v.28 no.5
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• pp.12-24
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• 2023

The Songji lagoon is brackish environment with a mixture of saline and fresh water, and the interaction of groundwater-lagoon water creates a physicochemical gradient. Although some studies have been conducted on the hydrological and geochemical characteristics of the Songji lagoon, microbial ecological studies have not yet been conducted. In this study, we investigated the effect of groundwater and surface water interaction on water quality as well as microbial community changes in the Songji Lagoon using 16S rRNA gene sequencing. Hydrochemical analyses show that samples were classified as 5 hydrochemical facies (HF) and hydrochemical facies evolution (HFE) revealed the intrusion phase was more dominant (57.9%) than the freshening phase (42.1%). Higher microbial diversity was found in freshwater in comparison to saline water samples. The microbial community at the phylum level shows the most dominance of Proteobacteria with an average of 37.3%, followed by Bacteroidota, Actinobacteria, and Patescibacteria. Heat map analyses of the top 18 genera showed that samples were clustered into 5 groups based on type, and Pseudoalteromonas could be used potential indicator for seawater intrusion.

• Journal of Species Research
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• v.13 no.3
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• pp.318-325
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• 2024

Bacterial communities residing on islands have a significant impact on the functioning and establishment of a unique isolated ecosystem. Notwithstanding, systematic research on the indigenous microbial resources of domestic islands has been lacking. In order to understand the biodiversity and potential bioresources, we conducted sampling in 2023 from coastal waters from various islands off the west coast of the Korean Peninsula, including Baengnyeongdo, Daebudo, Deokjeokdo, Jangbongdo, Yeonpyeongdo Islands, along with Somaemuldo Island along the south coast. The coastal seawater samples were used to unearth microbial resources through the standard dilution plating. In total, approximately 1,600 bacterial strains were isolated from the samples as single colonies and identified using 16S rRNA gene sequence analyses. Eighteen strains, exhibiting ≥98.7% 16S rRNA gene sequence similarity to bacterial species with validly published names but not previously reported in Korea, were categorized as unrecorded bacterial species in Korea. These unrecorded bacterial strains displayed phylogenetic diversity, representing three phyla, four classes, 9 orders, 13 families, and 18 genera. The unrecorded species were assigned to the classes Alphaproteobacteria (Aliiroseovarius, Kiloniella, Maritalea, Palleronia, and Roseobacter), Gammaproteobacteria (Aliamphritea, Aliivibrio, Enterovibrio, Francisella, Leucothrix, Pseudoalteromonas, Psychrobium, Shewanella, and Vibrio), Flavobacteriia (Aquimarina, Pseudofulvibacter, and Tenacibaculum), and Verrucomicrobiae (Roseibacillus). This study presents comprehensive descriptions of the taxonomic attributes of these unrecorded species, covering morphology, biochemistry, and phylogenetic position.

• Korean Journal of Microbiology
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• v.54 no.1
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• pp.60-68
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• 2018

A cold-active and alkaline serine protease (Pro21717) was partially purified from the Antarctic marine bacterium Pseudoalteromonas arctica PAMC 21717. On a zymogram gel containing skim milk, Pro21717 produced two distinct clear-zones of approximately 37 kDa (low intensity) and 74 kDa (high intensity). These were found to have identical N-terminal sequences, suggesting they arose from an identical precursor and that the 37 kDa protease might homodimerize to the more active 74 kDa form of the protein. Pro21717 displayed proteolytic activity at $0-40^{\circ}C$ (optimal temperature of $40^{\circ}C$) and maintained this activity at pH 5.0-10.0 (optimal pH of 9.0). Notably, relative activities of 30% and 45% were observed at $0^{\circ}C$ and $10^{\circ}C$, respectively, in comparison to the 100% activity observed at $40^{\circ}C$, and this enzyme showed a broad substrate range against synthetic peptides with a preference for proline in the cleavage reaction. Pro21717 activity was enhanced by $Cu^{2+}$ and remained stable in the presence of detergent surfactants (linear alkylbenzene sulfonate and sodium dodecyl sulfate) and other chemical components ($Na_2SO_4$ and metal ions, such as $Ba^{2+}$, $Mg^{2+}$, $Ca^{2+}$, $Zn^{2+}$, $Fe^{2+}$, $K^+$, and $Na^{2+}$), which are often included in commercial detergent formulations. These data indicate that the psychrophilic Pro21717 has properties comparable to the well-characterized mesophilic subtilisin Carlsberg, which is commercially produced by Novozymes as the trademark Alcalase. Thus it has the potential to be used as a new additive enzyme in laundry detergents that must work well in cold tap water below $15^{\circ}C$.

• Korean Journal of Microbiology
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• v.51 no.4
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• pp.382-388
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• 2015

Eleven protease-producing bacteria were isolated from the organisms' external shells and the inorganic materials collected from intertidal zone of Jeju Island, Republic of Korea. The samples were diluted serially, inoculated on Zobell agar plates with 1% skim milk and incubated at $20^{\circ}C$. Clear zone forming colonies were selected as protease-producing bacteria and each strain was identified based on the phylogenetic analysis with their 16S rDNA sequences. Strains JJM125, JJM129, YG47 and YG49 belong to the marine bacterial genus Pseudoalteromonas; strain JJM122 belong to the genus Microbulbifer; strains YG51, YG52, YG62 and YG63 belong to the genus Vibrio; and strain YG65 belong to genus Bacillus. Hence, the present study suggests that these protease producing bacteria could be further used to develop new varieties of protease with various biotechnological applications.

• Korean Journal of Ichthyology
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• v.29 no.1
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• pp.62-68
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• 2017

The Alaska pollock (Gadus chalcogrammus) belongs to the family Gadidae; it is a cold water fish, and has been developed as a novel aquaculture species in Korea. In this study, we describe ongoing surveillance for aquatic animal pathogens based on growth stages. We investigated bacterial flora in rearing water, and monitored pathogens; we also analyzed histopathological traits of abnormal fish. In rearing water, the total bacterial counts were $2.1{\times}10^3cfu/mL$ and Vibrio spp. (52%) were predominant in the larvae stage. In the juvenile and adult stages, the total bacterial counts were $3.4{\times}10^3$ and $3.2{\times}10^2cfu/mL$, respectively (with Pseudomonas sp. as the predominant species; 90% and 52%). This result revealed that the bacterial flora in rearing water changed depending on the feeding types. No virulent-bacteria or problematic viruses (VHSV, viral hemorrhagic septicemia virus; NNV, nervous necrosis virus; MBV, marine birnavirus) were detected from outwardly healthy fish using either culture or PCR assay. Some juveniles (less than 5%) had gas bubbles on the gill lamellae, degeneration of the corneal epithelium, and choroid gland degeneration, suggesting that these symptoms were caused by external injury and secondary infection by opportunistic bacteria. Disease management is important to cope with disease emergence in the novel aquaculture species Alaska pollock.