The ICTV's recommendation for how to write virus, species and other taxa names. (Updated September 16, 2020)
If I am talking about beta/alpha coronaviruses in general, is it one word or two: e.g. 'beta coronaviruses' or 'betacoronaviruses'? (No italics, correct)?
Would Betacoronavirus only be capitalized when explicitly referring to the genus (i.e. ...the genus Betacoronavirus contains...
When referring to the genus, the correct usage is to capitalize and italicize the name: "...the genus Betacoronavirus.".
For casual reference to the group of viruses, there is no "official" designation of names. In this case, my preference would be a single word: "... betacoronaviruses such as SARS-CoV...".
Elliot