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On NPR public radio news it was said that if the bacteria that is natural that assist in body function or just present in your body was put it into a ball it would weigh more or less 7 ounces (approximately 200 grams). I tried to find the exact quote but am still looking for it and will revise when I find it.

Can viruses assist in body function as in extending life in any way?

Can a body be 100% free of viruses of not how much would the total virus weigh if put in a ball?

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    $\begingroup$ It seems like after your edit you now have a bunch of questions rather than one. $\endgroup$
    – Bryan Krause ♦
    Commented Jan 22, 2019 at 22:30
  • $\begingroup$ Our analysis also updates the widely-cited 10:1 ratio, showing that the number of bacteria in the body is actually of the same order as the number of human cells, and their total mass is about 0.2 kg. (0.4 pounds) ncbi.nlm.nih.gov/pmc/articles/PMC4991899 $\endgroup$
    – bandybabboon
    Commented Jan 23, 2019 at 5:15
  • $\begingroup$ Possible duplicate of biology.stackexchange.com/q/74887/3340 $\endgroup$
    – WYSIWYG
    Commented Jan 24, 2019 at 13:29

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Viruses, in general, are obligately pathogenic i.e. they don't usually co-exist (as commensals or symbionts) with our body cells. Their mechanism of survival involves usurping of the host cell machinery to produce their own proteins and genetic material. However, as pointed out in the comments, there are some viruses such as the GBV-C which can infect the host but seldom cause any disease. Moreover, this virus has been shown to have a positive effect on the innate immune response and inhibitory effect on HIV [1].

(Also, have a look at: Do beneficial viruses exist? If so, what examples are there?)

In our genome, here are some remnants of viruses that had infected our ancestors long back in past. A prominent example is that of retrotransposons. Retrotransposons are DNA sequences that constitute a significant part of our genome and they are structurally similar to the genome of retroviruses (like HIV). Retrotransposons had been considered junk DNA in the past but recent studies have shown that they do play some important roles in our body. For example, L1 retrotransposons cause somatic diversity (genetic diversity at the cellular level) of neurons and may possibly contribute to increasing the plasticity of our brain[2,3]. Retrotransposons can also regulate gene expression[4].

Other than that, there may be infectious viruses that are present in the body but are dormant. These may become active later (when the conditions are conducive) and cause the disease in that individual or spread to another person.

You can perhaps calculate the weight of these viral remnants (retrotransposons). It won't provide any great insight to anyone. You just have to calculate the percentage of genome these DNA sequences occupy and multiply it with molecular weight of the genomic DNA and total number of cells in the body. I'll leave that exercise to you.

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    $\begingroup$ Viruses are not obligately pathogenic. There are a number of free viruses (i.e., viruses that are not retrotransposons) that are beneficial. GBV-C, for example. $\endgroup$
    – De Novo
    Commented Jan 23, 2019 at 17:00
  • $\begingroup$ There are also many many viruses that do not appear to be associated with any disease, but have not been demonstrated to be beneficial. There is much still to be learned about the human virome. $\endgroup$
    – De Novo
    Commented Jan 23, 2019 at 17:06

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