There are two accepted forms for possessive singular nouns ending in s:
Add an apostrophe (') after the existing s at the end of the word: bacillus'
Add an apostrophe s ('s) after the existing s at the end of the word: bacillus's
Examples:
This bacillus' function is to assist the decay of organic matter.
This bacillus's function is to assist the decay of organic matter.
Note: If you are a student, use the form that is preferred by your teacher.
Bacilli is plural. The singular is bacillus.
Bacillus subtilis is not a photoautotroph.
Bacillus are the type of bacteria which are causative agents of food poisoning. e.g. Bacillus Anthracis
The plural of bacillus is bacilli.
Bacillus and Clostridium
Quantum is singular, not singular possessive. The singular possessive form is quantum's.
Bacilli is plural. The singular is bacillus.
The plural form of the noun 'bacillus' is bacilli.
Museum is singular. Museum's is singular possessive. Museums is plural. Museums' is plural possessive.
The singular possessive pronouns are mine, yours, his, hers, and its. The singular possessive adjectives are my, your, his, her, and its.
The singular possessive of dish is dish's
Grave's is the singular possessive.
The singular possessive is test's.
The singular possessive is Martin's.
The singular possessive is fish's.
Buzz's is the singular possessive.
The singular possessive is biker's; the plural possessive is bikers'.