Classification, Morfology, Habitat & Life Cicle of Actinomycetes

 Actinomycetes are a group of Actinobacteria found in soil. These bacteria cause the “smell of rain” or petrichor when hit by rainwater. This process occurs because _Actinomycetes_ produce a metabolite called the aromatic compound geosmin, which is hydrolyzed by rainwater and then evaporates.

The classification of _Actinomycetes_ according to Lechevalier et al. (1971) is as follows:  

Kingdom: Bacteria  

Phylum: Actinobacteria  

Class: Actinobacteria  

Order: Actinomycetales  

Family: Actinomycetaceae  

Genus: _Actinomyces_  

Species: _Actinomyces_ sp.

Morphologically, _Actinomycetes_ bacteria are generally rod-shaped and Gram-positive with high guanine and cytosine content. _Actinomycetes_ are bacteria that have fungus-like characteristics because they have thin filaments like mold. The growth pattern of _Actinomycetes_ and fungi tends to be similar, but fungi are eukaryotes while _Actinomycetes_ are prokaryotic bacteria. _Actinomycetes_ are divided into two groups, namely _Streptomycetes_ and Rare-_Actinomycetes_, whose growth tends to be slower. In addition, their cell walls contain N-acetylmuramic acid. These bacteria do not have mitochondria but contain 70S ribosomes and a nuclear envelope ranging from 5-20 micrometers.

The body structure of _actinomycetes_ consists of fine threads called hyphae or mycelia. When on a solid surface, mycelium or mycelia can differentiate to form aerial hyphae with the aim of producing reproductive spores. Substrate mycelium produces spores by germinating and forming monopodial structures. The initial stage of spore formation is known as the budding process. Spores can form on the substrate, while aerial mycelium consists of single cells. These bacteria are facultative anaerobes that can grow with or without O₂. This type of bacteria is able to ferment carbohydrates. _Actinomycetes_ colonies can be easily distinguished because they are not slimy or mucoid.

Actinomycetes are bacteria that can live in various places such as soil and the sea.  

1. Soil: _Actinomycetes_ generally live in soil at a pH range for growth of 5-9 with an optimum pH around 7. The distribution of _Actinomycetes_ is highly determined by environmental factors such as pH. The role of _actinomycetes_ in soil is the degradation of complex polymers in the plant decomposition process. The role of this type of _Actinobacteria_ in the rhizosphere is to suppress pathogen growth and synthesize gibberellin and indole acetic acid. Waterlogged soil is not suitable for the growth of these bacteria due to the presence of spores. _Streptomycetes_ generally make up about 70% of microorganisms in soil.  

2. Sea: Marine _Actinomycetes_ can decompose cellulose, chitin, alginate, hydrocarbons, oil, etc. These organisms play an important role in degrading oil in aquatic environments. The suitable temperature for _Actinomycetes_ growth ranges from 25-30°C.

The life cycle of _Actinomycetes_ bacteria starts from various phases. According to Demain and Fang (1995) it is as follows:  

1. Germination: The germination phase is the phase where spores obtain a suitable environment or substrate for growth.  

2. Vegetative growth: This phase is the growth phase of hyphae or mycelium from primary mycelium to secondary mycelium.  

3. Coiling: The phase where bacterial mycelium coils.  

4. Septation: The phase where septa form between vegetative hyphae.  

5. Spore maturation: Mature septa will form spore chains, so that the spores become fragmented.  

6. Spore release: Spores detach and are free in the environment.