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Abstract Recently, methane has been considered a next-generation carbon feedstock due to its abundance and it is main component of shale gas and biogas. Methylomonas sp. DH-1 has been evaluated as a promising industrial bio-catalyst candidate. Succinate is considered one of the top building block chemicals in the agricultural, food, and pharmaceutical industries. In this study, succinate production by Methylomonas sp. DH-1 was improved by combining adaptive laboratory evolution (ALE) technology with genetic engineering in the chromosome of Methylomonas sp. DH-1, such as deletion of bypass pathway genes (succinate dehydrogenase and succinate semialdehyde dehydrogenase) or overexpression of genes related with succinate production (citrate synthase, pyruvate carboxylase and phosphoenolpyruvate carboxylase). Through ALE, the maximum consumption rate of substrate gases (methane and oxygen) and the duration maintaining high substrate gas consumption rates was enhanced compared to those of the parental strain. Based on the improved methane consumption, cell growth (OD600) increased more than twice, and the succinate titer increased by ~ 48% from 218 to 323 mg/L. To prevent unwanted succinate consumption, the succinate semialdehyde dehydrogenase gene was deleted from the genome. The first enzyme of TCA cycle (citrate synthase) was overexpressed. Pyruvate carboxylase and phosphoenolpyruvate carboxylase, which produce oxaloacetate, a substrate for citrate synthase, were also overproduced by a newly identified strong promoter. The new strong promoter was screened from RNA sequencing data. When these modifications were combined in one strain, the maximum titer (702 mg/L) was successfully improved by more than three times. This study demonstrates that successful enhancement of succinic acid production can be achieved in methanotrophs through additional genetic engineering following adaptive laboratory evolution.

Abstract Nutrient dynamics function globally, flowing from rivers to the ocean (estuarine–coastal zone), and are vulnerable to climate change. Microbial habitats can be affected by marine nutrient dynamics and may provide a clue to predict microbial responses to environmental heterogeneity in estuarine–coastal zones. We surveyed surface seawater in Gwangyang Bay, a semi-enclosed estuary in Korea, from 2016 to 2018 using a metabarcoding approach with prokaryotic 16S and eukaryotic 18S rRNA genes. Bacterial and microeukaryotic communities in these waters showed distinct local communities in response to environmental heterogeneity and community transition at spatiotemporal scales in the estuarine–coastal zone. The relative abundance of prokaryotic and eukaryotic operational taxonomic units suggested a microbial trophic interaction in the Gwangyang Bay waters. We found that the community assembly process in prokaryotic communities was primarily influenced by biological interaction (immigration–emigration), whereas that in eukaryotic communities was more affected by environmental stress (habitat specificity) rather than by biotic factors. Our findings in the Gwangyang Bay waters may provide information on underlying (biotic or abiotic) factors of the assembly process in microbial communities in the estuarine–coastal zone.

Spatial and temporal variability in the trophic base of food webs is an inevitable ecological attribute in aquatic ecosystems with the role of aquatic and terrestrial sources varying from system to system. Despite high algal biomass, an apparent increase in terrestrial detritus during the East Asian summer monsoon would be expected to alter the dominant food web base from the pre- to post-monsoon period. The δ13C and δ15N values of common aquatic invertebrates and fish were compared with those of their potential sources of organic matter across the upstream channel and lacustrine habitats during the pre- and post-monsoon periods in the Se-oak Stream system of Korea. The purpose was to identify the variability in trophic structure (niche and diversity) at the community level and to quantify the contribution of terrestrial and aquatic carbon sources to the food web base. The δ13C and δ15N values of the major potential organic matter sources differentiated allochthonous leaf litter and riparian vegetation from autochthonous biofilm and seston, but with no significant spatial and temporal changes. The δ13C values of consumers fell within a narrower range than that of organic matter sources, consistent with the instream biofilm and seston values. However, the consumer δ15N values spanned a broad range, increasing from invertebrates to fish. The resultant niche overlaps of consumers in the isotopic niche space between seasons and locations, their narrower horizontal niche breadths compared to organic matter sources, and the isotope mixing-model estimates indicated that aquatic production was the primary source of organic matter supporting the aquatic food webs. Overall, the results revealed a consistent dominance of autochthonous trophic bases in both lotic and lentic food webs before and after the summer monsoon. Our findings, which highlight the trophic importance of aquatic algal production facilitated by anthropogenic nutrients in this shallow, low-turbidity, and well-illuminated stream food web, may provide insight into ecosystem processes that counteract potential terrestrial-aquatic links to influence food web dynamics based on natural nutrient sources in deep, highly turbid, or shaded stream counterparts.

Knowledge of physiological responses of important shellfish species to rising temperatures is crucial in assessing the impacts of climate change on marine aquaculture production. The physiological components of energy balance that support growth performance were measured seasonally at different exposure temperatures in the ark clams (Anadara kagoshimensis) cultured in the shallow muddy bottom sediment in Yeoja Bay, Korea. We tested the effects of winter minimum (3–8°C) and summer maximum (23–28°C) temperature elevations on individual physiological processes (ingestion, respiration, egestion, and excretion) and the combined energetic physiology (scope for growth [SFG] and net growth efficiency [K2] measures). The seasonal cycle of dry flesh tissue weight (DW) was also investigated from January 2016 to November 2018, to compare its variation at contrasting cold vs. warm regimes. The rates of physiological components were related to DW, generating significant allometric equations. The weight exponents of the equations for ingestion rate and respiration rate were low at the winter minimum compared with the remaining season temperatures, indicating a higher thermal sensitivity in larger individuals. The physiological rates that were re-calculated for individual components based on estimates of the slope and intercept of the equations increased with increasing temperature, revealing an incapability of thermal acclimation and a temperature effect at seasonally different endogenous conditions. The thermal sensitivity (Q10) of the ingestion rate and respiration rate was reversed between the winter minimum and the summer maximum temperature elevations, yielding negative SFG and K2 values at 3 and 28°C. Furthermore, the interannual difference in the seasonal cycle of clam DW displayed variations in the period of increment prior to spawning and the post-spawning loss/recovery in association with its energy balance status in the winter and summer temperature conditions. Overall, these results indicate that warming is projected to affect physiological performance and the seasonal DW cycle of clams in different manners between winter and summer: physiological benefits and advanced weight gain vs. heat stress and progressive weight loss, respectively. The mechanistic adjustment of the clam energy balance across thermal conditions seems to explain the recent advancement in its seasonal biological cycle, as well as the failure in spat collection and the mass summer mortality observed at this culturing site.

The diet of the Antarctic toothfish (Dissostichus mawsoni) was analyzed using metabarcoding to determine whether spatiotemporal factors are related to its feeding ecology. A diet metabarcoding analysis was conducted for five years from 2016 to 2020 using 1,777 samples collected from two distantly located subareas, 88.3 and 58.4.1. Metabarcoding results revealed 105 prey haplotypes (29 families, 45 genera) in the stomach contents of D. mawsoni, which can serve as valuable genetic information for the accurate identification of piscine species inhabiting the Southern Ocean. Most of the stomach contents of D. mawsoni consisted of fish taxa, comprising 99.61% of read count, which is consistent with other studies indicating that D. mawsoni is piscivorous. The prey compositions were highly different between the two subareas (88.3 and 58.4.1) regardless of the year, indicating that the diet of D. mawsoni strongly reflects the fish assemblages in geographically different habitats. These results strongly suggest that the stomach contents are good ecological indicators for monitoring any changes in the marine ecosystem caused by either the fishery of D. mawsoni, the most voracious piscine predator in its habitat, or environmental changes. In addition, quantitative polymerase chain reaction results of the two most abundant Macrourus prey species of Antarctic toothfish, M. caml and M. whitsoni, showed that the distribution of these two species may be related to the dynamics of gyres, which flow along the Antarctic continent.

In this study, to determine the spatiotemporal variability of satellite-observed chlorophyll-a (Chl-a) concentrations in the East Sea (Japan Sea, EJS), monthly composite images were generated via noise processing using Level-2 MODIS Chl-a data from 2003 to 2020. Harmonic analysis was performed on time-series Chl-a data to present the spatial distribution of seasonal and intraseasonal variability with 1–4 cycles per year. In the EJS, seasonal cycles contributed less than approximately 30% to the total variance in Chl-a variability, indicating the existence of dominant interannual variability. Analysis of the temporal trend in Chl-a concentrations showed that they increased (< 0.06 mg m–3 yr–1) in most of the EJS over almost two decades (2003–2020). In recent years, in the areas showing positive trends in Chl-a, it tended to increase with time, especially in the northern part of the EJS. As a result of examining the trend associated with the physical environment that affects the long-term trend in Chl-a concentrations, sea surface temperature (SST) trends were mostly increased. The wind speeds showed a characteristic strengthening trend in the northeastern part of the EJS and the North Korean coast. Long-term changes in wind direction indicated strengthening of the northerly wind components on the Russian coast and the westerly components on the eastern coast of the Korean Peninsula. These wind changes were closely related to the Arctic Oscillation (AO) index variability in relation to the recent warming of the Arctic Ocean. When the AO index was greater than 1, the wind speed tended to be weakened and the SSTs showed a tendency to increase. This led to general increasing responses in Chl-a concentrations during positive AO. The summer SST anomaly revealed an inverse relationship between higher positive values during the La Niña period and lower ones during the El Niño period. When the amplitude of MEI (Multi-variate ENSO Index) was high (| MEI| > 1), the SST anomaly indicated an inverse correlation with the Chl-a concentration anomaly in the EJS. This study demonstrated the regional effects of climate change on Chl-a variability in the EJS in response to tropical–subtropical and arctic–subarctic interactions between ocean and atmospheric variations.

Coastal benthic communities in temperate regions have been influenced by climate change, including increasing sea-surface temperature. Nevertheless, scleractinian coral Alveopora japonica Eguchi, 1968, is thriving in shallow subtidal hard bottoms around Jeju Island, off the southern coast of Korea. The presence of this corals has negatively impacted subtidal kelp populations in Jeju Island. However, there is no study to document how the presence or absence of this coral relates to other benthic communities. This study investigated the benthos in three shallow subtidal sites (Shinheung (SH), Bukchon (BC), and Seongsan (SS)) in northern Jeju using underwater photography. Macro-benthic organisms appearing on a 1 × 20 m line transect installed at depths of 5, 10, and 15 m at each site were analyzed. Results showed that of the three sites investigated, A. japonica colonies were most abundant at BC, accounting for 45.9% and 72.8% of the total transect area at 10 m and 15 m, respectively. At SS, A. japonica occupied 15.3% of the total area at 15 m and less than 1% at 5 m and 10 m. The same at SH accounted for 10% of the total area at 5 m, and less than 1% at 10 m and 15 m. Dead and bleached colonies accounted for 1.2-11.5% and 1.8-5.7%, respectively, at 5, 10, and 15 m at three sites. At SS, canopy-forming brown algae Ecklonia cava and Sargassum spp. accounted for 20.2 and 24.3% of the total transect area, respectively, at 5 m depth. In contrast, the percent cover of E. cava and Sargassum spp. at SH and BC ranged from 0.1 to 1.8%, respectively. Moreover, non-geniculate coralline algae dominated the subtidal substrate at SH, ranging between 60.2 and 69% at 15 and 10 m. The low cover of A. japonica in SS (at 5 m) coincided with a high percent cover of canopy-forming brown algae. However, canopy-forming brown algae were rare at all depths at SH and BC and were dominated instead by coralline algae and the scleractinian corals. This study, by utilizing a non-destructive method, provides a baseline qualitative and quantitative information for understanding the site and depth-dependent distribution of A. japonica and algal populations, which is important to understand climate change related changes in benthic communities in Jeju and elsewhere.

A subpolar front (SPF) generated between the East Korea Warm Current (EKWC) and the North Korea Cold Current (NKCC) in the western margin of the East/Japan Sea has shifted northward in recent decades. This study investigated the biomass and composition of the phytoplankton assemblage in relation to hydrological and biogeochemical features in the shallow shelf and slope off the Korean coast from January to June in 2016 and 2017, to determine the mechanistic effects of SPF on spring–summer phytoplankton bloom dynamics. Monthly average depth-integrated chlorophyll a (Chl a) levels and the contribution of phytoplankton classes revealed bimodal diatom blooms in early spring and summer in the frontal zone. Canonical correspondence analysis showed that the distribution of high Chl a was associated with cold, low-salinity NKCC water in March 2016. No Chl a peak was observed in March 2017 when the warm saline EKWC water mass invaded. These results suggest that the NKCC intrusion acts as a forcing mechanism leading to enhanced phytoplankton biomass in the frontal zone. In contrast, positive correlations of Chl a concentration with water density and nutrient concentrations suggest that summer blooms were fed by the subsurface chlorophyll maximum (SCM) driven by shoaling of the pycnocline and nitracline. Varying water-column stratification determined the thickness of the SCM layer, driving year-to-year variability in the magnitude of diatom blooms. These findings further suggest that seasonal/interannual variability in the timing of algal blooms affects regional trophodynamics and hence could be an important factor in explaining ecosystem changes in this region.

We investigated the trophic dynamics between neustonic copepod communities and particulate organic matter (POM) sourced from contrasting water masses, i.e., high- and low-salinity areas, within the northeastern East China Sea. The sampling of neustonic copepod communities occurred three times in the summer (June, August, and September) of 2021, and considered the influx of the Yangtze River Diluted Water (YRDW) and the extension of the Tsushima Warm Current (TWC). To examine the relationship between the neustonic copepods and surface POM, we employed stable isotope techniques. Surprisingly, the neustonic copepod community exhibited a reluctance to feed on surface POM. The neustonic copepod community in the YRDW-dominated area in August showed higher δ13C values than those in the TWC-dominated area. The trophic groups within the neustonic copepod population appeared to consume selectively depending on the individual preferred prey sizes and composition. Using the POM from the water masses that affected the food sources consumed by neustonic copepods, we found a strong dependence on prey items originating from the TWC. This result suggests that the marine neustonic copepod community does not rely significantly on food sources derived from riverine freshwater. [ABSTRACT FROM AUTHOR]

Leopard cat (Prionailurus bengalensis euptilurus) is a small wild cat assessed as an endangered wildlife in Korea. There have been very few reports of their diseases. Herein, we describe fibrinous pleuritis caused by Streptococcus canis infection with excessive pleural effusion, hydropericardium, mild ascites, and liver fibrosis in a leopard cat. S. canis is a commensal microflora in domestic cats and often affects the upper respiratory tract inducing chronic and severe respiratory diseases. However, there is no literature regarding the S. canis in leopard cats. Therefore, we first report fibrinous pleuritis associated with an S. canis infection in a leopard cat. [ABSTRACT FROM AUTHOR]

Abstract Pulsed flows following heavy monsoon rain events alter riverine food webs, but their impact on headwater stream food webs across the continuum from forested canopy to open agricultural land use remains unclear. We investigated carbon and nitrogen stable isotopes in macroinvertebrates and fish in two tributaries of the Suyeung River, Korea, before and after heavy monsoon rains to assess changes in community trophic niches. Basal resources (leaf litter and biofilms) exhibited consistent δ13C and δ15N values across seasons, with biofilms showing higher δ13C values. δ15N values increased from forested to agricultural reaches, indicating varied nutrient inputs. Consumer isotope values remained stable over time but varied longitudinally, reflecting reliance on local resources. Trophic niches differed between watershed locations but overlapped seasonally. Despite a decrease in consumer δ13C ranges after heavy rainfalls, variations in their δ15N ranges and the ellipse centroid (SEAc) of isotopic niches between sites resulted in broadly consistent SEAc across locations and seasons. This indicates limited evidence for directional reshaping of food-web properties across channel reaches following monsoon rains. Downstream isotopic shifts suggest substantial agricultural influences on food webs. Overall, our findings highlight that monsoon rains may have minimal effects on the community trophic niches of stream food webs.

The walleye pollock, Gadus chalcogrammus (Pallas, 1814), is one of the most commercially and ecologically valuable species in the Northwestern Pacific. However, combined pressures of overfishing and environmental changes have led to a substantial decline in its production in Japan and Russia since the 1990s, and a collapse in Korea since the 2000s. The objective of this study was to comprehensively examine its genetic diversity and population structure with an extensive sampling effort of 16 populations across the Northwestern Pacific including South Korea, Japan, and Russia. A multiplex PCR assay composed of seven microsatellite markers revealed a moderate level of observed heterozygosity (Ho = 0.369–0.599), which is lower than that reported in previous studies of this species. All loci were highly polymorphic, with the mean PIC ranging from 0.608 to 0.793. The structure of the 16 populations was characterized by heterozygote deficiency, a modest effective allele number (Ne = 4.551–7.969), low genetic differentiation (FST = 0.000–0.054), a weak population structure, a genetic admixture, and no significant correlation between the genetic and geographic distance. These characteristics are typical of pelagic marine species with large population sizes due to a consistent gene flow among populations when there are no physical boundaries in the open ocean. The seasonal and country-specific genetic structure indicated that G. chalcogrammus populations in the Northwestern Pacific region should be managed as a single management unit. The findings from this study provide critical information for future genetic monitoring, conservation management, and the development of strategies aimed at restoring the populations of this species.