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. 2018 Feb;7(1):e00531.
doi: 10.1002/mbo3.531. Epub 2017 Sep 18.

The Lactococcus Lactis KF147 Nonribosomal Peptide Synthetase/Polyketide Synthase System Confers Resistance to Oxidative Stress During Growth on Plant Leaf Tissue Lysate

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Free PMC article

The Lactococcus Lactis KF147 Nonribosomal Peptide Synthetase/Polyketide Synthase System Confers Resistance to Oxidative Stress During Growth on Plant Leaf Tissue Lysate

Benjamin L Golomb et al. Microbiologyopen. .
Free PMC article

Abstract

Strains of Lactococcus lactis isolated from plant tissues possess adaptations that support their survival and growth in plant-associated microbial habitats. We previously demonstrated that genes coding for a hybrid nonribosomal peptide synthetase/polyketide synthase (NRPS/PKS) system involved in production of an uncharacterized secondary metabolite are specifically induced in L. lactis KF147 during growth on plant tissues. Notably, this NRPS/PKS has only been identified in plant-isolated strains of L. lactis. Here, we show that the L. lactis KF147 NRPS/PKS genes have homologs in certain Streptococcus mutans isolates and the genetic organization of the NRPS/PKS locus is conserved among L. lactis strains. Using an L. lactis KF147 mutant deficient in synthesis of NrpC, a 4'-phosphopantetheinyl transferase, we found that the NRPS/PKS system improves L. lactis during growth under oxidative conditions in Arapidopsis thaliana leaf lysate. The NRPS/PKS system also improves tolerance of L. lactis to reactive oxygen species and specifically H2 O2 and superoxide radicals in culture medium. These findings indicate that this secondary metabolite provides a novel mechanism for reactive oxygen species detoxification not previously known for this species.

Keywords: Lactococcus lactis; NRPS/PKS; Plant-associated bacteria; natural products; reactive oxygen species; secondary metabolites.

Figures

Figure 1
Figure 1
The hybrid NRPS/PKS from L. lactis KF147. Genes on the genomic island are colored as follows: two‐component transcriptional regulator (yellow), secondary metabolite biosynthesis enzymes (green), ABC transporter (orange), macrolide biosynthetic protein AvrD (purple), phytoene dehydrogenase (pink), DNA integration/recombination/inversion protein (red), and hypothetical proteins (white). Insertion of the genomic island is shown relative to L. lactis strains originating from different sources (strains IO‐1, CV56, and KLDS 4.0325) genes in blue. The fold‐induction of each gene in ATL relative to GM17 is shown in parentheses as determined previously (Golomb & Marco, 2015). N/C indicates no change in expression was observed. Gene expression results were not reported for llkf_RS06220, llkf_RS06235, and llkf_RS06240 because they are newly annotated open reading frames
Figure 2
Figure 2
Growth of L. lactis KF147 and BAL1 in ATL with paraquat. L. lactis KF147 and BAL1 were inoculated into 10 ml ATL containing 10 mmol/L paraquat and incubated at 30°C without aeration. The average ± SD of three replicate cultures is shown
Figure 3
Figure 3
Growth of L. lactis KF147 and BAL1 in GM17 under respiratory conditions with and without paraquat. L. lactis KF147 and BAL1 were inoculated into GM17 under respiratory conditions (continuous aeration and 10 μg/ml hemin) (a) or respiratory conditions and 20 mmol/L paraquat (b). Bacteria were incubated at 30°C in microtiter plates and OD was measured at 600 nm. The average ± SD of at least eight replicate cultures is shown

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