The growth of hyperaccumulator plants is often compromised by increased toxicity of metals like cadmium (Cd). However, extraction of such metals from the soil can be enhanced by endophytic microbial association. Present study was aimed to elucidate the potential of microbe-assisted Cd phytoextraction in hyperaccumulator Solanum nigrum plants and their interactions under varied Cd concentrations. An endophytic bacteria Serratia sp. RSC-14 was isolated from the roots of S. nigrum. In addition to Cd tolerance up to 4 mM, the RSC-14 exhibited phosphate solubilization and secreted plant growth-promoting phytohormones such as indole-3-acetic acid (54 μg/mL). S. nigrum plants were inoculated with RSC-14 and were grown in different concentrations of Cd (0, 10, and 30 mg Cd kg(-1) sand). Results revealed that Cd treatment caused significant cessation in plant growth, biomass, and chlorophyll content, whereas significantly higher malondialdehyde (MDA) and electrolyte production in leaves were observed in a dose-dependent manner. Conversely, RSC-14 inoculation relived the toxic effects of Cd-induced stress by significantly increasing root/shoot growth, biomass production, and chlorophyll content and decreasing MDA and electrolytes contents. Ameliorative effects on host growth were also observed by the regulation of metal-induced oxidative stress enzymes such as catalase, peroxidase, and polyphenol peroxidase. Activities of these enzymes were significantly reduced in RSC-14 inoculated plants as compared to control plants under Cd treatments. The lower activities of stress responsive enzymes suggest modulation of Cd stress by RSC-14. The current findings support the beneficial uses of Serratia sp. RSC-14 in improving the phytoextraction abilities of S. nigrum plants in Cd contamination.

Fungal endophytes have been characterized as producers of phytohormones and potent promoters of plant growth. In this study, two fungal endophytes, Fusarium tricinctum RSF-4L and Alternaria alternata RSF-6L, were isolated from the leaves of Solanum nigrum. Culture filtrates (CFs) from each isolate were initially screened for indole compounds, and assayed for their ability to promote the growth of Dongjin rice plants. Nearly all plant growth attributes examined (i.e., chlorophyll content, root-shoot length, and biomass production) were significantly enhanced upon treatment with fungal CFs. Subsequently, gas chromatography/mass spectrometry analyses were utilized to confirm the presence of phytohormones in the CF of each fungal endophytic isolate. These analyses revealed that RSF-4L and RSF-6L produced 54 and 30 µg/mL indole acetic acid, respectively, within their respective cultures. These findings suggest that the endophytes isolated in this study synthesize bioactive compounds that could play important roles in promoting plant growth.

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Serratia marcescens RSC-14 is a Gram-negative bacterium that was previously isolated from the surface-sterilized roots of the Cd-hyperaccumulator Solanum nigrum. The strain stimulates plant growth and alleviates Cd stress in host plants. To investigate the genetic basis for these traits, the complete genome of RSC-14 was obtained by single-molecule real-time sequencing. The genome of S. marcescens RSC-14 comprised a 5.12-Mbp-long circular chromosome containing 4,593 predicted protein-coding genes, 22 rRNA genes, 88 tRNA genes, and 41 pseudogenes. It contained genes with potential functions in plant growth promotion, including genes involved in indole-3-acetic acid (IAA) biosynthesis, acetoin synthesis, and phosphate solubilization. Moreover, annotation using NCBI and Rapid Annotation using Subsystem Technology identified several genes that encode antioxidant enzymes as well as genes involved in antioxidant production, supporting the observed resistance towards heavy metals, such as Cd. The presence of IAA pathway-related genes and oxidative stress-responsive enzyme genes may explain the plant growth-promoting potential and Cd tolerance, respectively. This is the first report of a complete genome sequence of Cd-tolerant S. marcescens and its plant growth promotion pathway. The whole-genome analysis of this strain clarified the genetic basis underlying its phenotypic and biochemical characteristics, underpinning the beneficial interactions between RSC-14 and plants.

Emerging evidence suggests that probiotics are beneficial in non-alcoholic fatty liver disease (NAFLD). This study aimed to explore the effects of two Lactobacillus plantarum strains, ATG-K2 and ATG-K6 (isolated from Korean fermented cabbage), in a rat model of high fat/high fructose (HF/HF) diet-induced NAFLD. Rats with NAFLD were randomized into four groups (HF/HF diet control, (HC); HF/HF diet with silymarin, (PC); HF/HF diet with ATG-K2, (K2); and HF/HF diet with ATG-K6, (K6)) with healthy rats on a normal diet serving as the negative control. After treatment, histopathological and biochemical analyses of the blood and liver tissue were conducted. In addition, fecal microbiota was analyzed using the MiSeq platform. Compared with HC rats, K2 and K6 rats experienced significantly lower body weight gain, displayed decreased hepatic lipid accumulation, had lower serum levels of aspartate aminotransferase and alanine aminotransferase, and showed increased antioxidant enzyme activities. Moreover, de novo lipogenesis-related genes were downregulated following K2 and K6 administration. The fecal microbiota of K2 and K6 rats contained a higher proportion of Bacteriodetes and a lower proportion of Fimicutes than that of HC rats. Taken together, our results suggest that L. plantarum strains ATG-K2 and ATG-K6 are potential therapeutic agents for NAFLD.Nutrients 2020, 12, 542 2 of 16 of the transcription factors, such as sterol regulatory element binding protein 1c (SREBP-1c) and CCAAT/enhancer-binding protein alpha (C/EBPα), which in turn regulate the expression of hepatic gluconeogenesis and DNL genes [6]. It follows that fructose intake increases liver gluconeogenesis and DNL and elevates blood glucose and TG levels in humans [8,9] Another cause of NAFLD is oxidative stress. Fat deposition occurring in the liver results in lipid peroxidation, and it promotes a variety of responses such as inflammation and fibrosis. Thus, antioxidants (e.g., silymarin, vitamin E) are proposed as candidates for NAFLD treatment [10,11]; however, there are no standard pharmacological therapeutic agents for NAFLD yet. Recently, emerging evidence suggests that the gut-liver axis is strongly related to NAFLD. There are several reports published clinical trials applying probiotics on NAFLD patients [12]. Lactobacillus bulgaricus and Streptococcus thermophiles treatment improved liver aminotransferases levels in adult NAFLD patients [13]. In addition, probiotic capsules containing Lactobacillus acidophilus, Bifidobacterium lactis, Bifidobacterium bifidum, and Lactobacillus rhamnosus, as a supplement also decreased liver aminotransferases levels in obese children with NAFLD [14]. These results indicate that the intake of certain probiotics has a beneficial effect on NAFLD.Lactobacillus plantarum, which plays a key role in the production of various fermented foods, is one of the most important species of lactic acid bacteria (LAB). L. plantarum is found in diverse environments, such as the soil and the human gut, and is considered a potential pro...