How to prove novel organism by sequencing

Question

[Mainul]

Dear Scientists,

Our group working with freshwater algae. We found a few novels species based on the microscopic observation. We also did 18s RNA sequence and blast with NCBI and founds that 3 organisms only hit 25% matches with unculture organism. its seems that 3 organism looks novel. So to prove a novel organism what kinds of further analysis we should perform. Thanks in advance for your valuable answer.

[Jean-Karim Heriche]

I don't think there's a fixed list of criteria. I would suggest you look at the literature (e.g. search PubMed with keywords 'new species' and algae) to see what current practice is in this domain.

[Kevin Blighe]

Interesting concept. I wonder if we could informatically define a new species based on distances in a phylogenetic analysis...? Different criteria in different fields, as you imply. [just thinking out loud]

[Jean-Karim Heriche]

As far as I can tell, morphological observations still carry a lot of weight but are often complemented by phylogenetic analysis. Here is an article exemplifying what I have in mind. Here is an article based mostly on phylogenetic analysis but still using some morphology for support. I don't think there's an easy thresholding of phylogenetic distance since the distances would depend on the clade and genes studied.

[Mainul]

So can I say it's novel based on blast result. Or should I go for more information analysis such as

1. Should I go with phylogenetic analysis to make it more accurate.
2. Dose have any experimental techie that proved novel species?

[GenoMax]

You can say anything but question is would experts in the area agree with what you are saying. You don't say what kind of an organism you are working with but you should consider previous papers in the subject area to see what people may have done towards identification of new species.

Found this interesting article from Nature on this topic.

For the most part, biologists agree that species are made up of organisms that are evolving together. And they also agree that for sexual organisms, shared reproduction within species and the evolution of reproductive barriers between species, are major factors that cause species to exist. Where biologists tend to disagree is how these general theoretical ideas should translate into methods for detecting and identifying species. In other words, biologists agree that these ideas help us answer the question of what species are, but they are not in agreement about how much these ideas help answer the question of how to identify species.