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.
The singular possessive of "ant" is "ant's" and the plural possessive is "ants'".
Museum is singular. Museum's is singular possessive. Museums is plural. Museums' is plural possessive.
The singular possessive pronouns are "my," "mine," "your," "yours," "his," "her," and "its."
The singular possessive of dish is dish's
The singular possessive form of "classmate" is "classmate's."
The singular possessive is Martin's.
The singular possessive is fish's.
Grave's is the singular possessive.
The singular possessive form of "test" is "test's".