Macrococcus
bovicus - carouselicus - caseolyticus - equipercicus

Mannheimia
glucosida - granulomatis - haemolytica - ruminalis - varigena

Maricaulis
maris

Marinibacillus
marinus

Marinilabilia
salmonicolor

Marinobacter
aquaeolei - hydrocarbonoclasticus

Marinobacterium
georgiense - jannaschii - stanieri

Marinococcus
albus - halophilus

Marinomonas
communis - mediterranea - vaga

Marinospirillum
megaterium - minutulum

Marmoricola
aurantiacus

Massilia
timonae

Megasphaera
elsdenii

Melissococcus
plutonius

Mesorhizobium
amorphae - ciceri - plurifarium - tianshanense

Methylobacterium
aminovorans - dichloromethanicum - fujisawaense - mesophilicum - organophilum - rhodesianum - rhodinum - zatmanii

Methylophaga
marina - sulfidovorans - thalassica

Methylopila
helvetica

Methylorhabdus
multivorans

Microbacterium
arabinogalactanolyticum - arborescens - aurantiacum - aurum - barkeri - chocolatum - dextranolyticum - esteraromaticum - flavescens - hominis - imperiale - keratanolyticum - ketosireducens - kitamiense - lacticum - laevaniformans - liquefaciens - luteolum - maritypicum - oxydans - saperdae - schleiferi - sp. - terrae - terregens - testaceum - thalassium - trichothecenolyticum

Microbispora
mesophila

Microbulbifer
hydrolyticus

Micrococcus
luteus - lylae - sp.

Microlunatus
phosphovorus

Micromonas
micros

Micromonospora
echinospora - matsumotoense

Moellerella
wisconsensis

Moraxella
atlantae - boevrei - bovis - canis - caprae - equi - lacunata - laennata - lincolnii - nonliquefaciens - osloensis - saccharolytica - sp.

Morganella
morganii

Moritella
japonica - marina

Morococcus
cerebrosus

Mycobacterium
abscessus - aichiense - alvei - asiaticum - aurum - austroafricanum - avium - bohemicum - bovis - branderi - brumae - caprae - celatum - chelonae - chitae - chlorophenolicum - chubuense - confluentis - conspicuum - cookii - diernhoferi - duvalii - elephantis - fallax - flavescens - fortuitum - gadium - gastri - gilvum - goodii - gordonae - haemophilum - hassiacum - heidelbergense - hiberniae - hodleri - immunogenum - intermedium - intracellulare - kansasii - komossense - kubicae - lentiflavum - madagascariense - mageritense - malmoense - marinum - moriokaense - mucogenicum - murale - neoaurum - nonchromogenicum - obuense - parafortuitum - peregrinum - phlei - poriferae - pulveris - rhodesiae - scrofulaceum - senegalense - septicum - simiae - smegmatis - sp. - szulgai - terrae - thermoresistibile - tokaiense - triplex - tuberculosis - tusciae - vaccae - wolinskyi - xenopi

Mycoplasma
adleri - agalactiae - arginini - arthritidis - auris - bovirhinis - buccale - capricolum - cottewii - fermentans - gallisepticum - genitalium - hominis - lagogenitalium - meleagridis - mycoides - neurolyticum - orale - pneumoniae - primatum - pulmonis - sturni - yeatsii

Myroides
odoratimimus - odoratus

Myxococcus
xanthus