Effective pH pretreatment and cell disruption method for real-time intracellular enzyme activity assay of a marine fungus covered with pigments

Transcriptomic analysis reveals resistance mechanisms of Klebsiella michiganensis to copper toxicity under acidic conditions

The aim of this study was to elucidate the effect of pH on bacterial resistance mechanisms to copper (Cu) stress by genomic and transcriptomic analysis. Klebsiella michiganensis cells were exposed to 0.5 mM CuCl₂ at pH 4 and 5. Lower pH (pH < 4) strongly inhibited K. michiganensis growth, while Cu stress and higher pH (pH > 5) induced Cu precipitation in the medium. Transcriptomic analyses indicated that two groups of genes related to quorum sensing (QS) systems (lsrABCDFGKR) and type II secretion systems (T2SS) (gspCDEFGHIJKLM) were significantly up-regulated at pH 4 only. These results suggest that T2SS may be induced and controlled by QS, thereby contributing to the formation of extracellular polymeric substances (EPS) and the secretion of proteins to prevent Cu ions from entering cells. Six Cu resistance genes (cusABF, copA, cueO, and gene05308) were more significantly up-regulated at pH 4 than at pH 5. In addition, the relative expression (log₂|FC=) of the sulfur assimilation genes cysHJIK was relatively higher at pH 4 than at pH 5, while the gene encoding organic sulfur metabolism, tauB, was also significantly up-regulated at only pH 4. These results indicate that the Cu efflux system can remove intracellular Cu ions from cells, and that the sulfur assimilation system is related to the detoxification of Cu ions. Furthermore, increased free Cu ions at lower pH (4) could induce communication signals among cells, thereby stimulating the response of T2SS-related genes in K. michiganensis to tolerate Cu stress. Consequently, the resistance of K. michiganensis to Cu stress is a multisystem collaborative process composed of intracellular and extracellular components.

Regulation of different polyketide biosynthesis by green light in an endophytic fungus of mangrove leaf

Light is an important environmental signal for many organisms. The light response reports of fungi usually focus on blue light and red light. Although the green light sensor has also been found in several fungi, the knowledge of the green light response in fungi is very limited. Halorosellinia sp. (No. 1403) is a light-sensitive endophytic fungus of mangrove leaf. In this study, we explored the specific effects of monochromatic blue light, red light, and green light on polyketides biosynthesis in Halorosellinia sp. (No. 1403), respectively. The major polyketides produced in Halorosellinia sp. (No. 1403) are octaketides (1403C and 1403R) and heptaketide (griseofulvin). All monochromatic light enhanced octaketide biosynthesis and inhibited heptaketide biosynthesis to some extent compared with the dark condition. Most prominently, the total production of octaketides was increased by 76%, and the production of heptaketide was decreased by 73% under green light in bioreactor. Therefore, green light can not only influence the secondary metabolism in fungi, but also it can influence different biosynthetic pathways in different ways. We speculate that the significant effect of green light on mangrove leaf endophytic fungus Halorosellinia sp. (No. 1403) may be a kind of environmental adaptation to plant photosynthesis.