Question

Ray fungi as diazotrophs are
A. Streptomyces and Mycoplasma
B. Gram negative monerans and symbiotically associated with xanthomonas
C. Gram positive monerans and symbiotically associated with Alnus
D. Chemoautotrophic $N_2$ – fixer

Answer 1

Hint: Diazotrophs are bacteria and archaea that fix atmospheric N (Nitrogen) gas into a lot of usable types like ammonia. A diazotroph could be an organism that's able to grow while not external sources of nitrogen is fixed.

Complete Answer:
- The word diazotroph means diazo ("di" = two + "azo" = nitrogen) that means "dinitrogen ($N_2$)" and troph meaning "pertaining to food or nourishment", in short dinitrogen utilizing.
- All diazotrophs contain iron-molybdenum or -vanadium enzyme systems.
- Two of the foremost studied systems are those of enterics pneumoniae and Azotobacter vinelandii. These systems are used due to their genetic tractableness and their quick growth factor.
- There are two types of diazotrophs: Free living (Anaerobes,facultative anaerobes, aerobes, and cyanobacteria) and symbiotic (Rhizobia, and frankies).
- Ray fungi belonging to Actinomyces is a genus of the Actinobacteria.
- Actinomyces species of bacteria make the colonies which have fungus-like branched structure of hyphae and that is why they are called ray fungus. They are gram positive and some species of nitrogen fixing bacteria live in with actinorhizal plants of the genus Alnus.

So, the correct answer is Gram positive monerans and symbiotically associated with Alnus.

Note: Diazotrophs are scattered across bacterium categorisation teams (as well as a handful of Archaea). Even inside a species which will fix N there are also strains that don't fix N.