Highlights on Chaetomium morphology, secondary metabolites and biological activates

Endophytic fungi always attract attention due to their generous production of bioactive and chemically novel compounds that have medical, agriculture, industrial applications. This review focused on Chaetomium as a model of endophytic fungi rich in therapeutic agents that have known medicinal and industrial application. Moreover, understanding the importance of this potent fungus encourage further studies to identify novel metabolites, and at the same time employing already known metabolites to evaluate their activity in order to be used in additional applications. Keyword: Chaetomium; Secondary metabolites; Biological activities, applications


Introduction
The application of microbial secondary metabolites in general, and fungal metabolites in particular in various fields of biotechnology has attracted the interests of many researchers, thanks to the bioactive properties of these metabolites which made them employed in various applications in pharmaceutical, industrial, and agricultural fields. Fungal endophytes are microorganisms that live inside the interior tissues of living plants without bringing on anydangerous reactions [1][2][3][4]. Generally, endophytes are generous source of novel and biologically active natural compounds with incredible healing potentials. Recently, remarkable pharmacological agents have been generated from endophytic fungi [5,6]. More than 50% of previously unknown biologically active substances have been isolated from endophytes [7]. Bio-pharmacological secondary metabolites originated from endophytes exhibit different antimicrobial, anticancer, antitumor, and anti-inflammatory activities [8]. The endophytic fungus, Chaetomium, is an excellent model that is used as a biotechnological tool in various fields. Chaetomium species are heterothallic fungi that found mainly in soil and organic compost and recently it was isolated from coral, soft coral, and marine algae, and Chaetomium are known for the production of secondary metabolites with vital biological activities. [9][10][11][12][13][14]. Different isolates of Chaetomium showed various mechanisms of antagonism against other pathogen fungi and they have been also reported to produce several antifungal metabolites [15,16]. As an example Chaetomium globosum Kunze Fr., has been identified as potential biocontrol agent against a numerous plant pathogens [17].
In this review, highlights on the description, ecology, biological activities and secondary metabolites produced by Chaetomium Species were presented.

Chaetomium description and ecology
The word 'endophytes' describes microbes colonizing internal living tissues of plants without causing any immediate harmful impacts [1]. Chaetomium sp. is a dematiaceous filamentous fungus that can be isolated found air, soil, and also from plant debris [18,19]. Chaetomium belongs to the class Pyrenomycetes (Ascomycotina), Order Sordariales and family Chaetomiaceae. There are about 95 species that have been identified under the genus Chaetomium worldwide [20]. As well as being a contaminant, Chaetomium sp. are also encountered as human pathogen. Some species are thermophilic and neurotropic in nature [21]. Chaetomium sp. are common fungal species with a worldwide ubiquitous distribution and are widespread in soil and on decaying plant materials but spore concentrations in outdoor air are not very high. Indoors, Chaetomium is found on wood, compost, sheet rock, straw, and similar cellulosic materials. It is also known as a soft-rot fungus for softwood and hardwood timber [22]. Colonies of Chaetomium are fast growing, colonies appear whitish cottony at the beginning, and turn grey to olive in color when become mature. From the reverse, color appear to be reddish tan or brownish black [23]. Chaetomium is ascomata globose, ellipsoid to ovate or obovate, ostiolate or non-ostiolate in a few species, with walls usually composed oftextura intricata or epidermoidea in surface view, or of textura angularis in a few species. Ascomatal hairs hypha-like, flexuous, undulate, coiled to simply or dichotomously branched, with verrucose surface, or smooth in a few species (Figure 1, 2). Asci clavate or fusiform with 8 biseriate or irregularly arranged ascospores, evanescent. Ascospores limoniform to globose, or irregular in a few species, bilaterally flattened, usually more than 7μm in length. Asexual morphs, if present, acremonium-like. Member of the genus Chaetomium

Some biological activities of Chaetomium metabolites
Due to their generosity in production of secondary metabolites such as chaetoglobosins, xanthones, anthraquinones, terpenoids, depsidones and steroids, researches were conducted to evaluate the biological activities of those compounds [26,27].

Conclusion
Emerging of antibiotic resistant microbes, as well as new diseases that threaten human life, besides the growing awareness of the dangerous impacts of using chemicals for pests and fungal control, are serious that require continuous search for potent sources of potent compounds from natural sources.
Recently, biocontrol of soil-borne pathogens has attracted attention as a promising support or alternative to currently used harmful chemicals. Chaetomium species in general, and Chaetomium globosum in particular, represent promising biocontrol agents that can get rid of pathogens and p-hydroxybenzaldehyde 3-benzyl-6-isobutyl piperazine-2,5-dione Uracil L-Alanin-L-leucin Cyclo-(L-proline-L-leucine) increase yield. Understanding the nutritional needs, mode of action, and quantification of fungi in soils are important factors that require further studies.
Development and easiness of isolation, and molecular identification of Chaetomium have facilitate discovering new species. Also, progress in chemical methods of extractions and invention of advanced instruments for chemical identification of compounds have open the way for the discovery of novel compounds with potential biological activities.
Using molecular markers, in depth study of interaction between Chaetomium and other microorganisms as well as their host plants are topics that require additional researches. Further investigations on the results of co-culturing Chaetomium with different bacterial species and its impact on the resulting metabolites are of extreme importance. Finally, investigating the potential bioactivities.