Abstract
Endophytic actinobacteria are one of the important pharmaceutical resources and well known for producing different types of bioactive substances. Nevertheless, detection of the novelty, diversity, and bioactivity on endophytic actinobacteria isolated from mangrove plants are scarce. In this study, five different mangrove plants, Avicennia marina, Aegiceras corniculatum, Kandelia obovota, Bruguiera gymnorrhiza, and Thespesia populnea, were collected from Beilun Estuary National Nature Reserve in Guangxi Zhuang Autonomous Region, China. A total of 101 endophytic actinobacteria strains were recovered by culture-based approaches. They distributed in 7 orders, 15 families, and 28 genera including Streptomyces, Curtobacterium, Mycobacterium, Micrococcus, Brevibacterium, Kocuria, Nocardioides, Kineococcus, Kytococcus, Marmoricola, Microbacterium, Micromonospora, Actinoplanes, Agrococcus, Amnibacterium, Brachybacterium, Citricoccus, Dermacoccus, Glutamicibacter, Gordonia, Isoptericola, Janibacter, Leucobacter, Nocardia, Nocardiopsis, Pseudokineococcus, Sanguibacter, and Verrucosispora. Among them, seven strains were potentially new species of genera Nocardioides, Streptomyces, Amnibacterium, Marmoricola, and Mycobacterium. Above all, strain 8BXZ-J1 has already been characterized as a new species of the genus Marmoricola. A total of 63 out of 101 strains were chosen to screen antibacterial activities by paper-disk diffusion method and inhibitors of ribosome and DNA biosynthesis by means of a double fluorescent protein reporter. A total of 31 strains exhibited positive results in at least one antibacterial assay. Notably, strain 8BXZ-J1 and three other potential novel species, 7BMP-1, 5BQP-J3, and 1BXZ-J1, all showed antibacterial bioactivity. In addition, 21 strains showed inhibitory activities against at least one “ESKAPE” resistant pathogens. We also found that Streptomyces strains 2BBP-J2 and 1BBP-1 produce bioactive compound with inhibitory activity on protein biosynthesis as result of translation stalling. Meanwhile, Streptomyces strain 3BQP-1 produces bioactive compound inducing SOS-response due to DNA damage. In conclusion, this study proved mangrove plants harbored a high diversity of cultivable endophytic actinobacteria, which can be a promising source for discovery of novel species and bioactive compounds.
Highlights
The increased prevalence of “ESKAPE” pathogens, along with the rapid development of multidrug resistances became the driving force in new antibiotics discovery (Spellberg et al, 2008; Bassetti et al, 2013; Pendleton et al, 2013; Singh et al, 2017)
A total of 101 isolates were confirmed as actinobacteria and phylogenetic analysis based on the partial 16S rRNA genes sequences revealed that the 101 endophytic actinobacterial strains were assigned to 28 genera in 7 orders of 15 families: Streptomyces, Curtobacterium, Mycobacterium, Micrococcus, Brevibacterium, Kocuria, Nocardioides, Kineococcus, Kytococcus, Marmoricola, Microbacterium, Micromonospora, Actinoplanes, Agrococcus, Amnibacterium, Brachybacterium, Citricoccus, Dermacoccus, Glutamicibacter, Gordonia, Isoptericola, Janibacter, Leucobacter, Nocardia, Nocardiopsis, Pseudokineococcus, Sanguibacter, and Verrucosispora (Figure 1)
A considerable diversity of endophytic actinobacteria was obtained from the mangrove plants collected in Beilun Estuary National Nature Reserve of Guangxi Zhuang Autonomous Region, China
Summary
The increased prevalence of “ESKAPE” pathogens, along with the rapid development of multidrug resistances became the driving force in new antibiotics discovery (Spellberg et al, 2008; Bassetti et al, 2013; Pendleton et al, 2013; Singh et al, 2017). It is becoming increasingly evident that un- and underexplored habitats are rich and new sources of actinobacteria for interesting novel bioactive metabolites, including antibiotics (Rateb et al, 2011; Manivasagana et al, 2014; Jiang et al, 2015; Mohammadipanah and Wink, 2015; Axenov-Gibanov et al, 2016; Hassan and Shaikh, 2017). Microbes have to adapt and evolve in metabolite and genetic level to resist the stress from their habitats, have the capability to synthesis of novel chemicals to carry out special biofunctions and bioactivities (Wilson and Brimble, 2009). A large number of new bioactive compounds produced by actinobacterial strains from special enviroments have been discovered in recent years. (Wilson and Brimble, 2009; Rateb et al, 2011; Xu et al, 2014; Hassan and Shaikh, 2017)
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