Classification, Morfology, Habitat & Life Cicle of Actinomycetes

Actinomycetes are microorganisms native to the sea and can be found on the surface of seawater, the seabed, in sediments, coral reefs, and in soil. Actinomycetes are prokaryotic, like bacteria, but possess mycelium and are classified as microbes with the potential to produce secondary metabolites.

Actinomycetes form symbiotic relationships with sponges on the outside of the body (extracellular exosymbiosis), inside the sponge (extracellular endosymbiosis), in the cytoplasm (intracellular symbiosis), and in the cell nucleus (intranuclear symbiosis). Actinomycetes are capable of producing bioactive compounds from antibiotics (70%), fungi (20%), and bacteria (10%). This type of microbe has been widely used in the pharmaceutical, animal feed, fisheries, and other industries. Commercial products that utilize actinomycete secondary metabolites include tetracycline, erythromycin, vancomycin, and streptomycin.

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.

The growth of microorganisms is divided into several phases as follows:  

1. Lag Phase  

In this phase, microorganisms adjust themselves to the new environment. Further growth can occur because various enzymes and intermediate substances are formed in this phase.  

2. Accelerated Growth Phase  

In this phase microorganisms begin to divide, but the generation time is still long. The lag phase and the accelerated growth phase are often collectively referred to as the lag phase.  

3. Logarithmic Growth Phase  

In this phase, the growth rate is fastest and the generation time is short and constant. Cell material synthesis is very rapid and constant. This condition continues until one or several nutrients are depleted or until toxic metabolic byproducts accumulate, thereby inhibiting microorganism growth.  

4. Decelerating Growth Phase  

In this phase, microorganism growth begins to be inhibited because required nutrients have decreased or toxic metabolic substances have accumulated.  

5. Stationary Phase or Constant Phase  

In this phase, microorganism growth is inhibited and a decline occurs because required nutrients have decreased or toxic metabolic substances have accumulated, causing the number of dead and living microorganisms to be equal.  

6. Accelerated Death Phase or Logarithmic Death Phase  

These two phases are often called the death decline phase. In this phase the division rate becomes zero while the death rate continues to increase. If this condition reaches the logarithmic death phase, the death rate becomes maximum.