• Front. Microbiol., 20 May 2021
• Sec. Antimicrobials, Resistance and Chemotherapy

Junho Lee¹, Hee Kyoung Kang¹, Hyeonsook Cheong¹ and Yoonkyung Park

• Department of Biomedical Science, Chosun University, Gwangju, South Korea
• ²Research Center for Proteineous Materials (RCPM), Chosun University, Gwangju, South Korea

Pine needles are used in several East Asian countries as food or traditional medicine. It contains functional components that exhibit a wide spectrum of pharmacological effects such as antioxidant, antimicrobial, anti-diabetic, and anti-inflammatory activities. We determined and characterized the novel antimicrobial peptides (AMPs) isolated from Pinus densiflora Sieb. et Zucc. The four active pine-needle (PN) peptides showed antimicrobial activity against foodborne bacteria with minimum inhibitory concentration (MIC) values within the range of 8–128 μg/ml. PN peptides showed no detectable hemolytic activity or cytotoxicity at the antimicrobial concentrations. The N-terminal amino acid sequence of the PN5 was identified using Edman degradation and Antimicrobial Peptide Database (APD) homology analysis showed that it was not identical to any other plant peptide. This suggests that PN5 can serve as an alternative therapeutic agent to be used in the food industry.

Introduction

Antimicrobial peptides (AMPs) play an important element in the innate immune system ranging from bacteria to plants, mammals, and insects (Hancock et al., 2016; Haney et al., 2019; Sathoff and Samac, 2019). Innate immunity is a defensive response in all multicellular organisms to combat pathogens. AMPs involved in these processes typically have a broad-spectrum activity against a wide range of Gram-positive and Gram-negative bacteria, fungi, and even certain viruses (Coates et al., 2018; Mookherjee et al., 2020). In the majority of cases, the mode of action of AMPs is related to the cytoplasmic membrane permeabilization. Plants are a source of bioactive compounds with various properties that are applicable in agriculture and medicine. Plants produced are short AMPs with a molecular mass less than 10 kDa; structurally, these are amphipathic and generally positively charged molecules at physiologically neutral pH values. They primarily play defensive roles such as acting as membrane-active antifungal, antibacterial, and antiviral agents (Tam et al., 2015; Dhama et al., 2018).

Many studies have been performed to evaluate pine needles (PN), and several compounds with antimicrobial activity have been detected (Ghaffari et al., 2019). The Korean red pine tree, Pinus densiflora, belongs to the family Pinaceae and is widely spread in East Asia (Korea, Japan, and China; Kim et al., 2020a). Various pine tree regions including needles, pollen, cones, and cortices are widely consumed as folk medicine, foods or dietary supplements for health promotion, antimicrobial, anti-inflammatory, and preservation effects (Hsu et al., 2006; Jeong et al., 2009). Pine bark protects collagen from the action of collagenase, while PNs exhibit anti-hypertensive effects and protect against oxidative DNA, protein, and lipid damage and oxidative stress-mediated apoptosis induced by hydroxyl radicals (Ku et al., 2007; Kim et al., 2010; Maimoona et al., 2011). Pine bark extracts are effective scavengers of free radicals and reactive oxygen species, can lower lipid levels in blood serum and may help to prevent disease and delay aging (Schafer et al., 2006; McGrath et al., 2015). PNs of form P. densiflora were used for folk medicine and for various disease prevention such as rheumatitis, hemorrhage, gastroenteric trouble, hypertension, and asthma (Kwak et al., 2006; Kim et al., 2020b). Recent scientific researches have shown that PNs form P. densiflora have antimicrobial, anti-viral, antioxidant, anti-mutagenic, anti-thrombosis, anti-asthmatic, and anti-inflammatory, and anti-cancer effects (Kwak et al., 2006; Park and Lee, 2011; Park et al., 2016; Ahn et al., 2018; Mostafa et al., 2018; Ha et al., 2020). However, the isolation and functional characterization of AMPs from PNs have been limited studies. Therefore, this study was conducted to identify and characterize AMPs from the needles of P. densiflora Sieb. et Zucc. We evaluated PN peptides to determine their antimicrobial ability against foodborne bacteria.

https://www.frontiersin.org/articles/10.3389/fmicb.2021.662462/full