## 4 Discussion
However, the L-serine treatment increased the intracellular ATP concentration and decreased the sensitivity to UVA irradiation (Figure 4b,d). L-serine treatment increases the ATP concentration through one-carbon metabolism, which is independent of F0F1-type ATP synthase [23]. [PERSON] et al. [29] reported that the ATP/ADP ratio was changed by oxidative stress under antibiotic treatment in _E. coli._ From these results, the intracellular ATP concentration controlled by not only F0F1-type ATP synthase but also other pathways, including one-carbon metabolism, may be crucial factors for modulating UVA sensitivity. General secretion is also known as the Sec-dependent or the type II secretion system (T2 SS). Many Gram-negative bacteria utilize the T2 SS to facilitate translocation of folded proteins from the periplasm through the outer membrane and likewise inwards from the extracellular environment [30]. Expression of outer membrane proteins (Omps), OmpU, OmpT, and OmpS, were all decreased and the outer membrane integrity was compromised in T2 SS mutants of _V. cholerae_[31; 32]. In this study, we observed a drastic increase in the extracellular content associated with mutations in general secretion pathway genes in _V. parahaemolyticus_ (i.e., _VP0136_ and _VP0140_; Figure 5a); [PERSON] et al. [33] reported similar findings in _V. cholerae_. In addition, this group determined that _V. cholerae_ T2 SS mutants were more sensitive to hydrogen peroxide and endogenous ROS formation than the WT strain [33]. From these results, factors associated with T2 SS-regulated outer membrane integrity are likely to be very important for sensitivity to UVA and oxidative stress. Apart from interactions within the outer membrane and T2 SS proteins, these latter components may also interact with other constituents of the cell envelope. As but one example, alterations in the structure of lipopolysaccharideacharide (LPS) have an immediate impact on the function of the T2 SS system in _Pseudomonas aeruginosa_[34; 35]. Recently, [PERSON] et al. [36] reported that T2 SS from _V. cholerae_ supported biofilm formation. Biofilms are microbial communities that are embedded in polysaccharides, nucleic acids, and associated extracellular protein matrix; they function to protect the resident bacteria from predators as well as from the effects of extracellular stress, the actions of antibiotics, and clearance by the immune system [37; 38; 39]. [PERSON] et al. [40] reported that biofilms containing _P. aeruginosa_ were more resistant to UVA irradiation than planktonic cells in culture. From these results, we conclude that biofilms controlled by the general secretion pathway of _V. parahemolyticus_ may also be associated with sensitivity to UVA irradiation. Ubiquinone (UQ), also known as coenzyme Q, is a lipophilic metabolite identified in organisms ranging from bacteria to mammals that includes a conserved quinone head group and an isoprenoid hydrophobic tail that varies in length among different species [41]. UQ-8 is located in the bacterial plasma membrane and has been described as an essential element underlying aerobic respiratory growth, gene regulation, and processes that rely on proton motive force [42; 43; 44]. Biosynthesis of UQ-8 takes place via a highly conserved pathway that involves a large number of genes (i.e., _ubi_) that have been identified by genetic studies [45]. The _ubiCA_ mutants all had altered patterns of UQ-8 biosynthesis and were hypersensitive to H\({}_{2}\)O\({}_{2}\); production of both O\({}_{2}\) and H\({}_{2}\)O\({}_{2}\) was significantly higher in the mutants than in the wild-type strain [46]. In our study, _VP0097_ (_ubiB_) and _VP0315_ (_ubiX_) mutants showed similar high sensitivities to UVA-LED that did not correlate with changes in UQ-8 concentrations (Figure 6). The _ubiX_ gene product catalyzes decarboxylation as part of the biosynthesis of UQ-8; inactivation of the gene leads to diminished levels of UQ-8 in target _E. coli_ cells [47].