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The bacterial genus Gordonia encompasses a variety of versatile species that have been isolated from a multitude of environments. Gordonia was described as a genus about 20 years ago, and to date, 39 different species have been identified. Gordonia is recognized for symbiotic associations with multiple hosts, including aquatic (marine and fresh water) biological forms and terrestrial invertebrates. Some Gordonia species isolated from clinical specimens are known to be opportunistic human pathogens causing secondary infections in immunocompromised and immunosuppressive individuals. They are also predominant in mangrove ecosystems and terrestrial sites. Members of the genus Gordonia are ecologically adaptable and show marked variations in their properties and products. They generate diverse bioactive compounds and produce a variety of extracellular enzymes. In addition, production of surface active compounds and carotenoid pigments allows this group of microorganisms to grow under different conditions. Several isolates from water and soil have been implicated in bioremediation of different environments and plant associated species have been explored for agricultural applications. This review highlights the prevalence of the members of this versatile genus in diverse environments, details its associations with living forms, summarizes the biotechnologically relevant products that can be obtained and discusses the salient genomic features that allow this Actinomycete to survive in different ecological niches. [ABSTRACT FROM AUTHOR]

Gordonia amicalis HS-11 has been enriched from a hydrocarbon contaminated tropical soil sample. The ability of this organism to utilize a triterpenic polyunsaturated hydrocarbon, squalene (2,6,10,15,19,23-hexamethyl-6,6,10,14,18,20-tetracosahexane) and the model saturated hydrocarbon n- hexadecane is described here. The isolate degraded squalene and n- hexadecane (79 ± 3.02 and 96 ± 4.11%, respectively) after eight days of incubation. The isolate produced an extracellular biosurfactant that reduced surface tension from 69 ± 2.83 to 40 ± 1.63 and 35 ± 2.34 mN m−1 with squalene and n- hexadecane as carbon sources, respectively, after 6 days. The Actinomycete cleaved squalene to geranylacetone and farnesyl acetaldehyde that were further utilized for supporting growth. n -Hexadecane was degraded via monoterminal oxidation and activities of important enzymes (alkane hydroxylase and alcohol dehydrogenase) were highest (215 ± 8.76 and 169 ± 6.02 units mg−1 protein, respectively) after four days. Cells grown on squalene were short and with n- hexadecane there were clumps of longer cells. Squalene and n -hexadecane-grown cell surfaces were smooth possibly due to extracellular surface active compounds. While growing on hydrophobic substrates, some cells were seen adhering to droplets and others were in the free form. The culture was able to simultaneously degrade hydrocarbons and produce two commercially relevant value-added products. The yield of the extracellular biosurfactant on n -hexadecane was 480 mg l−1 and cells grown on squalene and n- hexadecane also yielded carotenoids (2.3 ± 0.14 and 2.9 ± 0.10 mg g−1 dry cell weight, respectively). This is the first report on the utilization of squalene by Gordonia. Image 1 • Gordonia amicalis HS11 aerobically degraded squalene and n- hexadecane. • Geranylacetone and farnesyl acetaldehyde were squalene degradation intermediates. • n -Hexadecane was degraded via monoterminal oxidation. • Distinct morphological features were observed on squalene and n- hexadecane. • The isolate produced emulsifier and carotenoids as value-added products. [ABSTRACT FROM AUTHOR]

The Actinomycete Gordonia amicalis HS-11 produced orange pigments when cultivated on n -hexadecane as the sole carbon source. When cells of this pigmented bacterium were incubated with 1 mM chloroauric acid (HAuCl 4 ) or silver nitrate (AgNO 3 ), pH 9.0, at 25 °C, gold and silver nanoparticles, respectively, were obtained in a cell associated manner. It was hypothesized that the pigments present in the cells may be mediating metal reduction reactions. After solvent extraction and High Performance Liquid Chromatography, two major pigments displaying UV–vis spectra characteristic of carotenoids were isolated. These were identified on the basis of Atmospheric Pressure Chemical Ionization Mass Spectrometry (APCI-MS) in the positive mode as 1′-OH-4-keto-γ-carotene (Carotenoid K) and 1′-OH-γ-carotene (Carotenoid B). The hydroxyl groups present in the carotenoids were eliminated under alkaline conditions and provided the reducing equivalents necessary for synthesizing nanoparticles. Cell associated and carotenoid stabilized nanoparticles were characterized by different analytical techniques. In vitro free radical scavenging activities of cells (control, gold and silver nanoparticle loaded), purified carotenoids and carotenoid stabilized gold and silver nanoparticles were evaluated. Silver nanoparticle loaded cells and carotenoid stabilized silver nanoparticles exhibited improved nitric oxide (NO) and 1,1-diphenyl-2-picrylhydrazyl (DPPH) scavenging activities compared to their control and gold counterparts. This paper thus reports cell associated nanoparticle synthesis by G. amicalis , describes for the first time the role of carotenoid pigments in metal reduction processes and demonstrates enhanced free radical scavenging activities of the carotenoid stabilized nanoparticles. [ABSTRACT FROM AUTHOR]