Microbiological analysis, antimicrobial activity, heavy-metals content and physico-chemical properties of Fijian mud pool samples.

The hot springs are home to a rich bacterial diversity which could be the source of enzymes, antibiotics and many other commercially important products. Most of the hot springs present in Fiji are unexplored and their analysis of microbial diversity could be of great interest in facilitating various industrial, agricultural and medicinal applications. This study is an attempt to evaluate the heavy metal concentration and to analyze the comprehensive bacterial diversity of two Fijian thermal mud pools, namely Sabeto and Tifajek. The two hot springs have a pH of 7.28 to 7.19 and a temperature of 32.2 to 38.8 °C, respectively. Mean metal concentrations of the studied mud samples ranged from 4.758 to 6.870 mg/kg and followed a decreasing sequence as Fe > Mn > Zn > Na > Ni > Cd > Ca > Cr > Cu. Levels of Fe, Na, Mn, Zn, Ni, Cd, Ca, Cr, Cu in the mud pool samples were within World Health Organisation (WHO) limits, while Cd was above regulatory limits. The heavy metals analysis results showed that both mud pools had high values for Cd, above the WHO limit of 3 mg/kg. In addition, 8 strains of actinomycetes were successfully identified for the first time in the Sabeto mud pool, where most of them showed antibacterial activity. The genetic identification of most isolates was determined in BLASTn analyses of their 16S rRNA sequences. Isolates were identified as that of Streptomyces, Nocardia and Rhodococcus genus. Further, AntiSMASH results of the closest relatives of cultured actinobacteria have shown to produce antibiotics, natural pesticides and other compounds of various usage. This study also found no fecal coliforms and supports existing knowledge and practice of using Fijian thermal mud pools for their therapeutic properties. Overall, the presented work indicated that the studied mud pools have therapeutic properties, harboring wealth of bacteria with antibiotic profiles and were risk free from health-related issues of heavy metals and disease-causing pathogens. It provides great insight into the studied mud pools which serves as a baseline from which further heavy metal monitoring or mitigation programs and microbial researches can be conducted.

Marine Actinomycetes Associated with Stony Corals: A Potential Hotspot for Specialized Metabolites.

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.