Inhibition of Bacterial Peptidoglycan Cytopathy by Retina Pigment Epithelial PGRP2 Amidase

Peptidoglycan (PGN) recognition protein 2 (PGRP2; N-acetylmuramyl-L-alanine amidase (NAMAA)) activity in corneal epithelial cells is thought to inhibit corneal inflammation by reducing the PGN-induced cytokines. PGRP2 has not been reported in human retinal pigment epithelial (RPE) cells. RPE cell lysate NAMAA activity was measured densitometrically via cleavage of FITC-tagged muramyl dipeptide (FITCMDP). RPE lysate degradation of the cytopathic activity of nucleotide-binding oligomerization domain (NOD) receptor agonists was assessed by caspase-3 activation and DNA ladder detection and quantitation. PGRP2/NAMAA protein was detected in RPE cells by immunofluorescent antibody assay. RPE lysate NAMAA cleaved FITCMDP in a dose- and time-dependent manner. RPE lysate selectively inhibited PGN cytopathic activity of NOD1 agonists containing D-γ-glutamyl-meso-diaminopimelic acid and NOD2 containing L-alanyl-D-isoglutamine. The results suggest RPE PGRP2 amidase selectively degrades PGN that stimulate NOD-mediated cytopathic activity. The failure of RPE NAMAA to degrade pro-inflammatory PGN may play a role in bacterial retinopathies.

Luteolibacter luteus sp. nov., isolated from stream bank soil

A non-motile, Gram-stain-negative, rod-shaped and yellow-colored bacterium, designated G-1-1-1^T was obtained from soil sampled at Gwanggyo stream bank, Gyeonggi-do, Republic of Korea. Cells were aerobic, catalase positive, grew optimally at 25-30 °C and hydrolysed aesculin and casein. A phylogenetic analysis based on its 16S rRNA gene sequence revealed that strain G-1-1-1^T formed a lineage within the genus Luteolibacter. The closest members were Luteolibacter flavescens GKX^T (97.7% sequence similarity) and Luteolibacter arcticus MC 3726^T (97.3%). The sequence similarities with other members of the genus Luteolibacter were ≤ 93.9%. The genome of strain G-1-1-1^T was 6,412,079 bp long with 5176 protein-coding genes. The diagnostic amino acid of cell-wall peptidoglycan of strain G-1-1-1^T was meso-diaminopimelic acid. The only respiratory quinone was menaquinone-9 and the principal polar lipids were phosphatidylethanolamine, diphosphatidylglycerol, phosphatidylglycerol and unidentified phospholipids. The predominant cellular fatty acids were iso-C_14:0, C_16:1 ω9c, C_16:0, C_14:0 and anteiso-C_15:0. The DNA G + C content was 61.0 mol%. The anti-SMASH analysis of whole genome showed eight putative biosynthetic gene clusters responsible for various secondary metabolites. Based on genomic, chemotaxonomic, phenotypic and phylogenetic analyses, strain G-1-1-1^T represents a novel species in the genus Luteobacter, for which the name Luteolibacter luteus sp. nov. is proposed. The type strain is G-1-1-1^T (= KACC 21614^T = NBRC 114341^T).