Sharing the properties of both bacteria and fungi, actinobacteria are widely distributed in both terrestrial and aquatic ecosystems, especially in soil. And here they play an important role in recycling refractory biomaterials by separating complex polymer mixtures in dead plants, animals and fungal materials. In addition, these bacteria are considered as biotechnologically valuable bacteria used for secondary metabolite production.
About 10,000 bioactive metabolites are produced by actinobacteria, 45% of all bioactive microbial metabolites discovered. Streptomyces bacteria species in particular produce industrially important microorganisms as they are a rich source of various useful bioactive natural products with potential applications. Although they have various applications, some actinobacteria have their own negative effects on plants, animals, and humans.
Soil remains the most important habitat for actinobacteria, with streptomycetes as the main component of its population. Streptomyces appeared to be the most abundant breed isolated in each study, according to numerous reports. Terrestrial bacteria have a variety of interesting antimicrobial potentials. Oskay et al. Have isolated actinobacteria with the ability to produce new antibiotics with high antibacterial activity. In the anoxic mangrove rhizosphere, species have been found abundantly, such as streptomyces, micromonospora, and nocardioform, 1,000 to 10,000 times smaller than arable land due to tidal action. Similarly, they produce new cytotoxic metabolites isolated from Nocardia Mangrove soil that strongly inhibit human cell lines such as gastric adenocarcinoma.
The sweet soil is also considered to be an extremely terrestrial environment and a microcolleus food source that only certain species, especially actinobacteria are often used to. There are several reports showing the distribution of actinobacteria in various locations such as sandy, black alkaline, sandy loam, alkaline sweet and subtropical sweet soil. In the study of Nithya et al., 134 morphologically distinguishable actinobacteria were isolated from 10 different desert soil samples and it was found that the isolates have varying levels of antibacterial activity against bacterial pathogens. Likewise, the rhizosphere plays an important role in the microbial community in the transformation of stubborn plant organic matter. For this reason, the rhizosphere zone is considered one of the best habitats for the isolation of these microorganisms. In the study of Priyadharsini et al., They isolated 45 morphologically different colonies from 12 different paddy field soils and observed their ability to inhibit their growth.
Actinobacteria are commonly found in aquatic habitats that can sometimes be washed out from the surrounding terrestrial habitats. It is vitally important to interpret their numbers and types in the light of information about organisms. It is known that Thermoactinomyces and rhodococcus coprophilus actinobacterial propagules are good indicators of the terrestrial component in water and sediments. Resistant endospores thermoactinomyces are produced in self-heating composts, overheated feeds and topsoil. However, they can be in aquatic habitats where they are deposited in muds and sediments. It has been assumed that these thermophiles cannot grow at ambient temperatures in most aquatic habitats. Similarly, the resting cocal stage R. coprophilus passes into freshwater and marine habitats, where they can survive, but probably do not grow.
Cross’s work has proven that actinobacteria can be easily isolated from freshwater areas. Some of the main types of actinobacteria living in freshwater are as follows:
Endospore forming thermoactinomyces,
Actinoplanes are usually found in soils, rivers or lakes, and the spore vesicles of these organisms have the ability to withstand prolonged drying, but secrete their motile spores to disintegrate when rehydrated. Zoospores are mobile with a tuft of flagella exhibiting chemotaxis and require an exogenous energy source. Micromonospora are also considered a common freshwater actinobacteria, they have been found to be native to such habitats where they transform cellulose, chitin and lignin. Numerous reports suggest that in micromonospora streams, rivers, river sediments and these are considered to be an integral part of aquatic microflora. Johnston and Cross found that streptomycetes fail to grow in various lakes, particularly deeper mud layers where micromonospora is dominant.
Another study by AI-Diwany et al found thermoactinomycetes isolated from micromonospora and the Wharfe river in West Yorkshire, with an increased number of micromonospora in the adjacent soil. In a study, it was determined that micromonospora spores stay in freshwater habitats where they can remain dormant for several years. Although Streptomycetes spores are also consistently in freshwater and marine habitats, there is little evidence that they can be active in such environments. The existence of aquatic streptomycetes has been claimed, but AI-Diwany et al. Found a high degree of correlation between streptomycetes, fecal counts. However, other types of freshwater bacteria are as follows:
• Actinomadura madurae,
• Mycobacterium kansasii,
• Nocardia species,
The concentration of hydrophobic spores and hyphae at the water and air interface can increase the number of streptomycetes, micromonospora and micromonospora. Evidence clearly shows that actinobacteria can become active in the freshwater ecosystem in the presence of suitable substrates and growth conditions rather than specifically adapting themselves to living in such an environment.
When comparing actinobacterial diversity in terrestrial environments, the greatest biodiversity is in the oceans. The marine environment is an undiscovered source of its new diversity and therefore new metabolites. Marine actinobacteria living in an extremely different environment produce different types of bioactive compounds compared to terrestrial ones. They have to adapt from extreme high pressure and anaerobic conditions at temperatures just below 0-8 ° C in the deep seabed to high acidic conditions at temperatures above 8-100 ° C, near hydrothermal vents in the mid-ocean ridges. Rhodococcus marinonascene, the first marine species to be characterized, supports the presence of marine actinobacteria. Members of this genus have been identified as marine actinobacteria and they are as follows:
• Aeromicrobium channel,
• Williamsia Maris,
• Native verrucosispora,
Grossart et al. Reported that actinobacteria make up about 10% of the bacteria that colonize marine organic aggregates, and their antagonistic activities can be very important in sustaining their existence, affecting the degradation and mineralization of organic matter. The presence of native actinobacteria in the oceans and their distribution in different marine environments and habitats has been confirmed by several recent studies. Innagi and his team isolated various marine actinobacteria, such as dietzia maris, rhodococcus erythropolis, and kocuria erythromyx, from the submarine sediment core collected at a depth of 1225 meters off Hokkaido. Jensen and his team isolated five new phyllotype actinomycetes from marine sediment collected around the island of Guam. Similarly, actinobacteria were isolated from sponges collected at a depth of 10,923 meters in Challenger Deep off Marianas, the deepest cliff, and they are as follows:
Dhanasekaran and his team investigated for primary antibacterial activity among 17 species of actinobacteria that they identified from soil samples belonging to the salinity areas of Cuddalore, Parangipettai. As a result of this research, they found that those with streptomyces spp and saccharomonospora sp had promising antimicrobial activity against different bacteria. The compound & # 946; -lactam, an antibacterial methyl, was isolated and characterized by Dhanasekaran et al. In Porto Novo saline soil. In another study, actinobacteria were isolated from soil and sediment samples from different locations in the Muthupet Mangrove area. These; Streptomyces sp CC17 – SM13, Streptosporangium sp SH15 and Micropolispora sp S22, also anopheles mosquito larvae showed the highest larvicidal activity.
All of the actinobacteria mentioned have been isolated from marine environments such as deep seafloor, invertebrates, coastal soil and deep sea sediments. In addition, these bacteria represent unique ecosystems that cannot be found anywhere else in the world. Likewise, these isolates produce a variety of new metabolites. Despite limited dredging efforts in the seas to date, it has more than its counterparts on land lately.
Writer: Ozlem Guvenc Agaoglu