The antimicrobial activity of zinc against group B Streptococcus is strain-dependent across diverse sequence types, capsular serotypes, and invasive versus colonizing isolates

Background Streptococcus agalactiae or Group B Streptococcus (GBS) is an encapsulated gram-positive bacterial pathobiont that commonly colonizes the lower gastrointestinal tract and reproductive tract of human hosts. This bacterium can infect the gravid reproductive tract and cause invasive infections of pregnant patients and neonates. Upon colonizing the reproductive tract, the bacterial cell is presented with numerous nutritional challenges imposed by the host. One strategy employed by the host innate immune system is intoxication of bacterial invaders with certain transition metals such as zinc. Methodology Previous work has demonstrated that GBS must employ elegant strategies to circumnavigate zinc stress in order to survive in the vertebrate host. We assessed 30 strains of GBS from diverse isolation sources, capsular serotypes, and sequence types for susceptibility or resistance to zinc intoxication. Results Invasive strains, such as those isolated from early onset disease manifestations of GBS infection were significantly less susceptible to zinc toxicity than colonizing strains isolated from rectovaginal swabs of pregnant patients. Additionally, capsular type III (cpsIII) strains and the ST-17 and ST-19 strains exhibited the greatest resilience to zinc stress, whereas ST-1 and ST-12 strains as well as those possessing capsular type Ib (cpsIb) were more sensitive to zinc intoxication. Thus, this study demonstrates that the transition metal zinc possesses antimicrobial properties against a wide range of GBS strains, with isolation source, capsular serotype, and sequence type contributing to susceptibility or resistance to zinc stress.

Effect of Salicylic Acid Foliar Application on Two Wheat Cultivars Grown under Zinc Stress

The aim of this study was to investigate the effect of foliar application of salicylic acid (SA) on alleviating Zn stress in young wheat plants. Two rigorous pot experiments were conducted with two spring wheat cultivars growing on soil artificially contaminated with Zn. The experimental design included three levels of soil contamination with Zn: 0, 300 and 700 mg kg−1, and three levels of SA concentration: 0, 0.5 and 1 mM. Foliar spray of SA was applied twice at an interval of two weeks. Wheat biomass was harvested two months after plant emergence. Both cultivars showed similar biomass reduction due to Zn phytotoxicity, but differed in the accumulation and distribution of this metal in the plant. The positive effect of SA foliar application was obtained only for one of the two tested cultivars, where a reduction in the Zn translocation from the roots to the aboveground part was observed. As a consequence, the decrease in biomass caused by the toxicity of Zn was limited. A greater positive effect of SA application on wheat biomass was observed at 700 than at 300 mg kg−1 Zn in soil. The different responses of the cultivars to the SA was probably related to their different defense mechanisms against Zn stress.

Genome-wide analysis of the lignin toolbox for morus and the roles of lignin related genes in response to zinc stress

Mulberry (Morus, Moraceae) is an important economic plant with nutritional, medicinal, and ecological values. Lignin in mulberry can affect the quality of forage and the saccharification efficiency of mulberry twigs. The availability of the Morus notabilis genome makes it possible to perform a systematic analysis of the genes encoding the 11 protein families specific to the lignin branch of the phenylpropanoid pathway, providing the core genes for the lignin toolbox in mulberry. We performed genome-wide screening, which was combined with de novo transcriptome data for Morus notabilis and Morus alba variety Fengchi, to identify putative members of the lignin gene families followed by phylogenetic and expression profile analyses. We focused on bona fide clade genes and their response to zinc stress were further distinguished based on expression profiles using RNA-seq and RT-qPCR. We finally identified 31 bona fide genes in Morus notabilis and 25 bona fide genes in Fengchi. The putative function of these bona fide genes was proposed, and a lignin toolbox that comprised 19 genes in mulberry was provided, which will be convenient for researchers to explore and modify the monolignol biosynthesis pathway in mulberry. We also observed changes in the expression of some of these lignin biosynthetic genes in response to stress caused by excess zinc in Fengchi and proposed that the enhanced lignin biosynthesis in lignified organs and inhibition of lignin biosynthesis in leaf is an important response to zinc stress in mulberry.

Genome-Wide Identification of Metal Tolerance Genes in Potato (Solanum Tuberosum): Response to Two Heavy Metal Stress

Metal tolerance proteins play an important role in the transport and tolerance of divalent heavy metals in plant species. Potatoes are an important food crop whose yields can be deeply affected by heavy metals. However, there is a lack of information concerning the members and function of the MTP gene family in Solanum tuberosum. In this study, we identified and screened 11 MTP genes in potatoes which we named as StMTP1 to StMTP11 based on their positions on the chromosomes. Phylogenetic analysis divided these 11 MTP genes into three subfamilies; Mn-MTP, Zn-MTP and Zn/Fe-MTP. HXXXD and DXXXD conserved motifs were found on or around the transmembrane domain II and transmembrane domain V of these proteins. The highly conserved histidine and aspartic acid residues may be related to the transport of metal ions. Quantitative real-time polymerase chain reaction (qRT-PCR) analysis showed that the expression levels of StMTP9 and StMTP10 in leaf tissues increased by around 24-fold following cadmium stress for 24 hours. We hypothesize that StMTP9 and StMTP10 respond to cadmium stress. StMTP11 showed the highest level of expression in stem tissues after 6 hours of zinc stress at more than 13 times the level of expression in controls indicating that StMTP11 is more sensitive to zinc stress. In summary, our results further the current understanding of the molecular mechanisms regulated by members of the MTP gene family in plant responses to heavy metal stress.

Correction to: Effect of salicylic acid foliar application on growth, glandular hairs and essential oil yield in Salvia officinalis L. grown under zinc stress

An amendment to this paper has been published and can be accessed via the original article.