Microbial secondary metabolites are an important source of antibiotics currently available for combating drug-resistant pathogens. These important secondary metabolites are produced by various microorganisms, including Actinobacteria. Actinobacteria have a colossal genome with a wide array of genes that code for several bioactive metabolites and enzymes. Numerous studies have reported the isolation and screening of millions of strains of actinomycetes from various habitats for specialized metabolites worldwide. Looking at the extent of the importance of actinomycetes in various fields, corals are highlighted as a potential hotspot for untapped secondary metabolites and new bioactive metabolites. Unfortunately, knowledge about the diversity, distribution and biochemistry of marine actinomycetes compared to hard corals is limited. In this review, we aim to summarize the recent knowledge on the isolation, diversity, distribution and discovery of natural compounds from marine actinomycetes associated with hard corals. A total of 11 new species of actinomycetes, representing nine different families of actinomycetes, were recovered from hard corals during the period from 2007 to 2022. In addition, this study examined a total of 13 new compounds produced by five genera of actinomycetes reported from 2017 to 2022 with antibacterial, antifungal and cytotoxic activities. Coral-derived actinomycetes have different mechanisms of action against their competitors.
Bioprospecting of novel antibiotics has been the conventional norm of research fostered by researchers worldwide to combat drug resistance. With the exhaustion of incessant leads, the search for new chemical entities moves into uncharted territories such as the deep sea. The deep sea is a furthermost ecosystem with much untapped biodiversity thriving under extreme conditions. Accordingly, it also encompasses a vast pool of ancient natural products. Actinobacteria are frequently regarded as the bacteria of research interest due to their inherent antibiotic-producing capabilities. These interesting groups of bacteria occupy diverse ecological habitats including a multitude of different deep-sea habitats. In this review, we provide a recent update on the novel species and compounds of actinomycetes from the deep-sea environments within a period of 2016–2022. Within this period, a total of 24 new species of actinomycetes were discovered and characterized as well as 101 new compounds of various biological activities. The microbial communities of various deep-sea ecosystems are the emerging frontiers of bioprospecting.
Forests are increasingly becoming fragmented and declining due to natural causes and human-induced activities. The latter creates an imbalance which put the survival of vulnerable species such as those of avifauna at risk. Honeyeaters are group of birds common in Fiji, with certain species strictly confined to specific habitats. This study is an attempt to compare the abundance and foraging behaviours of three sympatric honeyeaters namely Kikau wattled honeyeater, Orange-breasted myzomela and Giant honeyeater at two contradicted sites (USP campus and Colo-i-Suva Forest Reserve). The survey was carried out using point count method along three different transect routes of approximately 2 Km on each study sites . A higher species diversity and abundance was observed in Colo-i-Suva Forest Reserve than in USP campus. Kikau wattled honeyeater are more populated at USP campus due to adequate nectar-producing plants. Whereas both Orange-breasted myzomela (highly adaptable bird species) and Giant honeyeater (forest specifics) are frequent in Colo-i-Suva Forest Reserve. All exhibited a wider range of foraging techniques across forest vertical strata and plant species, except for Giant honeyeater (not observed). The statistical analysis showed that there is a significant difference (p < 0.05) in abundance as well as between the number of honeyeater species in both sites across the forest vertical strata. However, there is no significant difference in the foraging behaviour and the number of honeyeaters found foraging on diverse plant species (p > 0.05).
Crown of thorns starfish (Acanthaster planci) are coral predators with advantages of having toxicity in their venom and tissue regeneration capabilities. With all these characteristics, only a handful of studies have highlighted the association of microorganisms with this organism. Crown of thorns starfish are common in Fiji and their analyses of microbial diversity for secondary metabolites could be of great interest to the scientific community. This study is an attempt to investigate Fijian-based A. planci for their venom and associated actinomycetes antibacterial activity and further identify the type of enzymes present in the crude venom extract. The CoTS venom extract (0.192 g) harbor enzymes such as gelatinase, caesinase, and amylase. An abundant and potent actinomycete strain, represented as FJA1 showed antibacterial activity against Enterococcus faecium with an inhibition zone of 10 mm. Moreover, all pathogenic test microorganisms were resistant against concentrations of 500 µg and 1 mg of A. planci venom extract.
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