Nature of the Nitrogen Compounds Supporting Phototrophic Growth of the Marine Cryptomonad Hemiselmis virescens*

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Abstract
SYNOPSIS. Previous claims of a specific amino add‐nitrogen requirement for growth of Hemiselmis virescens have been disproved. The photosynthetic cryptomonad grows well on ammonium ion (at subtoxic concentrations) as sole N‐source but cannot utilize nitrate‐or nitrite‐N. Although the organism utilizes glycine efficiently, other amino acids are poor N‐sources, and only L‐glutamine, L‐cysteine, L‐cystine, and L‐tryptophan gave evidence of limited growth. Glycine peptides, derivatives (sarcosine, hippuric acid), and homologous relatives (β‐alanine, taurine) gave no growth. Among other amino compounds tested, only D‐glucosamine and D‐galactosamine supported some growth. Urea and some of its derivatives (alloxan, parabanic acid) were efficiently utilized, while other derivatives (biuret, guanidine, hydantoin, hydantoic acid, allantoin, creatinine) failed to support growth. All purines tested (adenine, hypoxanthine, xanthine, guanine, uric acid) gave moderate to good growth, while the pyrimidines cytosine, uracil, thymine were not utilized. No dark growth was obtained from any of the compounds supporting phototrophic growth. The capacity for efficient utilization of glycine, urea, and some of the purines may have ecologic significance.
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