Hydrogen peroxide and expression of hipI-superoxide dismutase are associated with the development of secondary cell walls in Zinnia elegans

A special form of a CuZn-superoxide dismutase with a high isoelectric point (hipI-SOD; EC 1.15.1.1) and hydrogen peroxide (H2O2) production were studied during the secondary cell wall formation of the inducible tracheary element cell-culture system of Zinnia elegans L. Confocal microscopy after labelling with 2',7'-dichlorofluorescin diacetate showed H2O2 to be located largely in the secondary cell walls in developing tracheary elements. Fluorescence-activated cell sorting analysis showed there were lower levels of H2O2 in the population containing tracheary elements when H2O2 scavengers such as ascorbate, catalase, and reduced glutathione were applied to the cell culture. Inhibitors of NADPH oxidase and SOD also reduced the amount of H2O2 in the tracheary elements. Furthermore, addition of these compounds to cell cultures at the time of tracheary element initiation reduced the amount of lignin and the development of the secondary cell walls. Analysis of UV excitation under a confocal laser scanning microscope confirmed these results. The expression of hipI-SOD increased as the number of tracheary elements in the cell culture increased and developed. Additionally, immunolocalization of a hipI-SOD isoform during the tracheary element differentiation showed a developmental build-up of the protein in the Golgi apparatus and the secondary cell wall. These findings suggest a novel hipI-SOD could be involved in the regulation of H2O2 required for the development of the secondary cell walls of tracheary elements.     

Animal Rennets as Sources of Dairy Lactic Acid Bacteria

The microbial composition of artisan and industrial animal rennet pastes was studied by using both culture-dependent and -independent approaches. Pyrosequencing targeting the 16S rRNA gene allowed to identify 361 operational taxonomic units (OTUs) to the genus/species level. Among lactic acid bacteria (LAB), Streptococcus thermophilus and some lactobacilli, mainly Lactobacillus crispatus and Lactobacillus reuteri, were the most abundant species, with differences among the samples. Twelve groups of microorganisms were targeted by viable plate counts revealing a dominance of mesophilic cocci. All rennets were able to acidify ultrahigh-temperature-processed (UHT) milk as shown by pH and total titratable acidity (TTA). Presumptive LAB isolated at the highest dilutions of acidified milks were phenotypically characterized, grouped, differentiated at the strain level by randomly amplified polymorphic DNA (RAPD)-PCR analysis, and subjected to 16S rRNA gene sequencing. Only 18 strains were clearly identified at the species level, as Enterococcus casseliflavus, Enterococcus faecium, Enterococcus faecalis, Enterococcus lactis, Lactobacillus delbrueckii, and Streptococcus thermophilus, while the other strains, all belonging to the genus Enterococcus, could not be allotted into any previously described species. The phylogenetic analysis showed that these strains might represent different unknown species. All strains were evaluated for their dairy technological performances. All isolates produced diacetyl, and 10 of them produced a rapid pH drop in milk, but only 3 isolates were also autolytic. This work showed that animal rennet pastes can be sources of LAB, mainly enterococci, that might contribute to the microbial diversity associated with dairy productions.     

Prospective Identification of Malaria Parasite Genes under Balancing Selection

Background

Endemic human pathogens are subject to strong immune selection, and interrogation of pathogen genome variation for signatures of balancing selection can identify important target antigens. Several major antigen genes in the malaria parasite Plasmodium falciparum have shown such signatures in polymorphism-versus-divergence indices (comparing with the chimpanzee parasite P. reichenowi), and in allele frequency based indices.

Methodology/Principal Findings

To compare methods for prospective identification of genes under balancing selection, 26 additional genes known or predicted to encode surface-exposed proteins of the invasive blood stage merozoite were first sequenced from a panel of 14 independent P. falciparum cultured lines and P. reichenowi. Six genes at the positive extremes of one or both of the Hudson-Kreitman-Aguade (HKA) and McDonald-Kreitman (MK) indices were identified. Allele frequency based analysis was then performed on a Gambian P. falciparum population sample for these six genes and three others as controls. Tajima''s D (TjD) index was most highly positive for the msp3/6-like PF10_0348 (TjD = 1.96) as well as the positive control ama1 antigen gene (TjD = 1.22). Across the genes there was a strong correlation between population TjD values and the relative HKA indices (whether derived from the population or the panel of cultured laboratory isolates), but no correlation with the MK indices.

Conclusions/Significance

Although few individual parasite genes show significant evidence of balancing selection, analysis of population genomic and comparative sequence data with the HKA and TjD indices should discriminate those that do, and thereby identify likely targets of immunity.