Seong Jang

Relationship between groundwater and climate change in South Korea

Climate change has resulted in a gradual increase in the surface temperature and significantly variable precipitation in different regions of the world. Linear regression of the groundwater levels in Korea between 2000 and 2010 revealed a decreasing trend with a slope of −29.2 mm/yr; −29.6 mm/yr in the wet season and −32.0 mm/yr in the dry season. Mann-Kendall and Sen’s tests were carried out using the groundwater levels and groundwater temperatures at 78 locations in South Korea between 2000 and 2010. The groundwater levels showed a trend in ~50% of the 78 groundwater level datasets, of which ~70% exhibited a decreasing trend at the 95% confidence level. This decreasing trend in the groundwater levels appears to be related to a change in the precipitation in South Korea because more abundant rainfall in the wet season each year does not contribute significantly to groundwater recharge, whereas less rainfall that occurs in the dry season can cause a decrease in the groundwater level. Linear regression of the groundwater temperatures revealed a slope of 0.1006 °C/yr between 2000 and 2010 with a gentler slope (0.08 °C/yr) in summer (June–September), showing that the increase in surface temperature has an impact on increasing the groundwater temperature. In this situation of climate change in Korea, the paradigm of groundwater management strategy needs to be altered properly.

Gut symbiotic bacteria stimulate insect growth and egg production by modulating hexamerin and vitellogenin gene expression

ABSTRACT Recent studies have suggested that gut symbionts modulate insect development and reproduction. However, the mechanisms by which gut symbionts modulate host physiologies and the molecules involved in these changes are unclear. To address these questions, we prepared three different groups of the insect Riptortus pedestris: Burkholderia gut symbiont‐colonized (Sym) insects, Burkholderia‐non‐colonized (Apo) insects, and Burkholderia‐depleted (SymBurk‐) insects, which were fed tetracycline. When the hemolymph proteins of three insects were analyzed by SDS‐PAGE, the hexamerin‐&agr;, hexamerin‐&bgr; and vitellogenin‐1 proteins of Sym‐adults were highly expressed compared to those of Apo‐ and SymBurk‐‐insects. To investigate the expression patterns of these three genes during insect development, we measured the transcriptional levels of these genes. The hexamerin‐&bgr; gene was specifically expressed at all nymphal stages, and its expression was detected 4–5 days earlier in Sym‐insect nymphs than that in Apo‐ and SymBurk‐‐insects. However, the hexamerin‐&agr; and vitellogenin‐1 genes were only expressed in adult females, and they were also detected 6–7 days earlier and were 2‐fold higher in Sym‐adult females than those in the other insects. Depletion of hexamerin‐&bgr; by RNA interference in 2nd instar Sym‐nymphs delayed adult emergence, whereas hexamerin‐&agr; and vitellogenin‐1 RNA interference in 5th instar nymphs caused loss of color of the eggs of Sym‐insects. These results demonstrate that the Burkholderia gut symbiont modulates host development and egg production by regulating production of these three hemolymph storage proteins. HighlightsGut symbionts are known to modulate host development and egg production.Expressions of hemolymph proteins are specifically changed by presence of gut symbiont.Burkholderia symbiont promotes the hosts development and fecundity via symbiosis‐affected host molecule.This study describes molecular cross‐talk between insects and gut symbionts.

Predicting long-term change of groundwater level with regional climate model in South Korea

Global climate change causes a high variability in precipitation and surface temperature increase in the world. Global climate models (GCMs) are effectively used to predict climate change at a global scale. In contrast, regional climate models (RCMs) can more efficiently predict climate change scenarios for a small territory such as South Korea. We estimated the groundwater level change in four drainage basins (the Han River, Nakdong River, Geum River, and Yeongsan-Sumjin River basins) in South Korea over the period 2000–2012, and then predicted the groundwater level change from 2000 to 2100 using a water budget model, considering RCMs with RCP 4.5 and RCP 8.5 scenarios. A distinct trend in the groundwater levels of each drainage basin was detected via the inversely close relationship with precipitation patterns of the drainage basin, showing a decrease in the groundwater level in relation to the increasing precipitation trend of the RCM scenarios. It is also proposed that the precipitation amount during the dry season more dominantly affects groundwater recharge than during the wet season.

Insecticidal activity of the metalloprotease AprA occurs through suppression of host cellular and humoral immunity

&NA; The biochemical characterization of virulence factors from entomopathogenic bacteria is important to understand entomopathogen‐insect molecular interactions. Pseudomonas entomophila is a typical entomopathogenic bacterium that harbors virulence factors against several insects. However, the molecular actions of these factors against host innate immune responses are not clearly elucidated. In this study, we observed that bean bugs (Riptortus pedestris) that were injected with P. entomophila were highly susceptible to this bacterium. To determine how P. entomophila counteracts the host innate immunity to survive within the insect, we purified a highly enriched protein with potential host insect‐killing activity from the culture supernatant of P. entomophila. Then, a 45‐kDa protein was purified to homogeneity and identified as AprA which is an alkaline zinc metalloprotease of the genus Pseudomonas by liquid chromatography mass spectrometry (LC‐MS). Purified AprA showed a pronounced killing effect against host insects and suppressed both host cellular and humoral innate immunity. Furthermore, to show that AprA is an important insecticidal protein of P. entomophila, we used an aprA‐deficient P. entomophila mutant strain (&Dgr;aprA). When &Dgr;aprA mutant cells were injected to host insects, this mutant exhibited extremely attenuated virulence. In addition, the cytotoxicity against host hemocytes and the antimicrobial peptide‐degrading ability of the &Dgr;aprA mutant were greatly decreased. These findings suggest that AprA functions as an important insecticidal protein of P. entomophila via suppression of host cellular and humoral innate immune responses. HighlightsP. entomophila showed high insecticidal activity against host R. pedestris.AprA, an alkaline zinc metalloprotease, is the major insecticidal protein of P. entomophila.AprA kills host R. pedestris by suppression of both host cellular and humoral innate immunity.