I believe that microorganisms can be considered as communities that are part of an ecosystem. They perform functions interact with each other, with other organisms, and with the physical environment. From another point of view, I believe that a host organism can be considered an ecosystem for the microorganisms that live inside it.

Yes of course. While microorganisms form a part of a larger ecosystem, each and every individual microorganism is also an ecosystem in itself. The cell contents including several organelles, cytoplasm and several other microbes within the cell all are inhabitants of this micro ecosystem. The various cell organelles are also sometimes identified as entities which were once able of independent existence having evolved to live together in harmony as a part of a larger individual. For example, the ribosomes are considered to be bacteria and mitochondria and plastids are considered to be blue-green algae. The term ecosystem can be interpreted according to various spatial dimensions. It just depends the way we and the inhabitants of the ecosystem looks at it. Ecosystem is a space where its life forms are dependent on one another and the so called non-living immediate environment around it. While in common parlance, we see ecosystem as a larger area as per our vision like a forest, lake, etc., a microbe can also be an ecosystem for its sub-microbe life forms.

Well said Manoj Chandran and Rodrigo Weber Felix . Yes, I can be considered

Manoj Chandran , sorry to say but you have misinterpreted the term 'ecosystem', which should include I) the biotic component consisting of several interacting species and ii) the changeable environment. The first and the second parts are interacting. The populations within the biotic component are also interacting but they have the freedom to move around, leave the community or come back, there is competition between species and competitive exclusion of a looser. There are no hard rules of predetermined behavior and no a fixed composition as in the case of a single microbial cell or a single Metazoan organism. Each human body has its internal structure without freedom of having, say, two hearts, and four kidneys.

Ayomi Pabasara we can use your expression in metaphorical meaning, e.g. 'A microbial culture is a kind of 'ecosystem' over long incubation time when spontaneous mutations create heterogeneity of the formerly pure homogeneous population'

Nicolai S Panikov There are open ecosystems and closed ecosystems as well. In case of a lake, for example, a fish do not have the freedom to leave the ecosystem and come back. In case of human body, for example, there are several organisms inside the body for whom the digestive system or its particular organs itself would be its ecosystem. There are organisms which can move around various systems within the human body. There are organisms which can even move out and re-enter the human body. The term ecosystem is a matter of interpretation. For some, it may be a 'habitat' and a collection of habitat an 'ecosystem', for others the same habitat may be composed of several micro-habitat making the 'habitat' an 'ecosystem, not to forget that each of those have abiotic components as well with whom they also interact throughout. I am fascinated by the term 'microcosmos' too as when we say cosmos, usually what immediately comes to our mind is the cosmos with respect to space and universe. Similarly, the term 'ecosystem' can also have various interpretations apart from definitions given in the books. Thanks for the critical comments on my interpretation of 'ecosystem'. I liked the 'kidney' comment. If one sees the evolutionary context, for example in a microbe, the functions that a kidney does is done by several organelles to clean up impurities in the cytoplasm. During the evolutionary process, the elementary processes were combined to a specific 'organ'. In short, kidney or heart is not a singularity, but a grand functional multiplicity. They have capability of independent existence (can be transplanted to another being) to an extent, but highly relies upon and is interdependent on other organs and functional control including their abiotic environment, both within the human body and also outside the human body (eg. oxygen levels in the air we breath)

Manoj Chandran. Sure, some of your thoughts do make sense. It is better to be creative than pedantic. Having said that, we should anyway try our best to use correctly the well-established scientific terms. Otherwise, scientists will stop understanding each other. The term 'ecosystem' belongs to this well-established category and it is already reserved by ecologists. If you want to express, say, the idea of the complexithe of a single microbial cell, use other words. 'It is like a city', 'like a marketplace', 'factory' etc.

Every organism benefit life and death of each other and evolve with inherited skills in next to next generation. As part of humans who are choosy must decide which organism they want to benefit in their body for growth and keep the organisms away from their body as far as they do not obstruct the growth of a human being in the environment created by them to live with the charms of humanity and resources they had for survival and living as a human with body and mind and soul. The shelter room and wash room and food preparation room in which humans live are entirely different from living environment of the other organisms. It needs more decisions and higher discipline on the grounds of basics for humans of all age. Human living is not enough if human do not communicate with the same species. Example: A Pink Bougainvillea and a White Bougainvillea is planted with their roots together or nearby then in few years we can see the white Bougainvillea is flowering with some pinkness and some Pink Bougainvillea will flower with whiteness. The scientific changes in both the Bougainvillea plant have beautiful vision to humans who see it as the work is done by them. Regards, Love & Compassion, Pankaj