Macrococcus
bovicus - brunensis - carouselicus - caseolyticus - equipercicus - hajekii - lamae

Macromonas
bipunctata

Magnetospirillum
gryphiswaldense - magnetotacticum

Mahella
australiensis

Malikia
granosa - spinosa

Malonomonas
rubra

Mannheimia
glucosida - granulomatis - haemolytica - ruminalis - varigena

Maribacter
dokdonensis - ulvicola

Maricaulis
maris - parjimensis - salignorans - sp. - virginensis - washingtonensis

Marichromatium
gracile - purpuratum

Marinibacillus
marinus

Marinilabilia
agarovorans - salmonicolor

Marinilactibacillus
piezotolerans

Marinithermus
hydrothermalis

Marinitoga
camini - hydrogenitolerans - piezophila

Marinobacter
aquaeolei - aquaolei - bryozoorum - daepoensis - flavimaris - hydrocarbonoclasticus - koreensis - lipolyticus - sp.

Marinobacterium
georgiense - jannaschii - stanieri

Marinococcus
albus - halophilus - halotolerans

Marinomonas
communis - dokdonensis - mediterranea - polaris - pontica - vaga

Marinospirillum
insulare - megaterium - minutulum

Marinovum
algicola

Marmoricola
aurantiacus

Martelella
mediterranea

Massilia
albidiflava - aurea - dura - lutea - plicata - timonae

Mechercharimyces
asporophorigenens - mesophilus

Megamonas
hypermegale

Megasphaera
cerevisiae - elsdenii - micronuciformis - paucivorans - sueciensis

Meiothermus
cerbereus - chliarophilus - ruber - silvanus - taiwanensis

Melissococcus
plutonius

Melittangium
boletus - lichenicola

Mesonia
algae

Mesophilobacter
marinus

Mesorhizobium
amorphae - chacoense - ciceri - huakuii - loti - mediterraneum - plurifarium - thiogangeticum - tianshanense

Metallosphaera
hakonensis - prunae - sedula

Methanimicrococcus
blatticola

Methanobacterium
aarhusense - alcaliphilum - beijingense - bryantii - congolense - espanolae - formicicum - ivanovii - oryzae - palustre - sp. - subterraneum - thermaggregans - uliginosum

Methanobrevibacter
acididurans - arboriphilicus - curvatus - cuticularis - filiformis - gottschalkii - oralis - ruminantium - smithii - sp. - thaueri - woesei - wolinii

Methanocalculus
chunghsingensis - halotolerans - pumilus - taiwanensis

Methanocaldococcus
fervens - indicus - infernus - jannaschii - vulcanius

Methanococcoides
alaskense - burtonii - methylutens - sp.

Methanococcus
aeolicus - maripaludis - sp. - vannielii - voltae

Methanocorpusculum
aggregans - bavaricum - labreanum - parvum - sinense

Methanoculleus
bourgensis - chikugoensis - marisnigri - palmolei - submarinus - thermophilus

Methanofollis
aquaemaris - formosanus - liminatans - tationis

Methanogenium
boonei - cariaci - frigidum - marinum - organophilum - sp.

Methanohalobium
evestigatum - sp.

Methanohalophilus
euhalobius - halophilus - mahii - portucalensis - sp.

Methanolacinia
paynteri

Methanolobus
bombayensis - oregonensis - taylorii - tindarius - vulcani

Methanomethylovorans
hollandica - thermophila

Methanomicrobium
mobile

Methanomonas
methylovora

Methanoplanus
endosymbiosus - limicola - petrolearius

Methanopyrus
kandleri

Methanosaeta
concilii - harundinacea

Methanosalsum
zhilinae

Methanosarcina
acetivorans - baltica - barkeri - calensis - lacustris - mazei - semesiae - siciliae - sp. - thermophila - vacuolata

Methanosphaera
cuniculi - stadtmanae

Methanospirillum
hungatei

Methanothermobacter
defluvii - marburgensis - thermautotrophicus - thermoflexus - thermophilus - wolfeii

Methanothermococcus
okinawensis - thermolithotrophicus

Methanothermus
fervidus - sociabilis

Methanothrix
thermophila

Methanotorris
formicicus - igneus

Methylobacillus
flagellatus - fructoseoxidans - glycogenes - sp.

Methylobacter
luteus

Methylobacterium
adhaesivum - aminovorans - aquaticum - chloromethanicum - dichloromethanicum - extorquens - fujisawaense - hispanicum - isbiliense - lusitanum - mesophilicum - nodulans - organophilum - podarium - radiotolerans - rhodesianum - rhodinum - sp. - suomiense - thiocyanatum - variabile - zatmanii

Methylocaldum
gracile

Methylocapsa
acidiphila - acidophila

Methylocella
tundrae

Methylococcus
capsulatus - thermophilus - ucrainicus

Methylocystis
methanolicus - parvus - pyreformis

Methylomicrobium
alcaliphilum

Methylomonas
clara - methanica - rubra - sp.

Methylophaga
alcalica - marina - sulfidovorans - thalassica

Methylophilus
glucoseoxidans - leisingeri - methylotrophus - sp.

Methylopila
capsulata - helvetica

Methylorhabdus
multivorans

Methylosarcina
fibrata - quisquiliarum

Methylosinus
sp. - sporium - trichosporium

Methylotenera
mobilis

Methylovorus
glucosotrophus

Microbacterium
aerolatum - arabinogalactanolyticum - arborescens - aurantiacum - aurum - barkeri - chocolatum - dextranolyticum - esteraromaticum - flavescens - foliorum - gubbeenense - halophilum - halotolerans - hominis - hydrocarbonoxydans - imperiale - keratanolyticum - ketosireducens - kitamiense - koreense - lacticum - laevaniformans - liquefaciens - luteolum - maritypicum - natoriense - oleivorans - oxydans - paludicola - paraoxydans - phyllosphaerae - resistens - saperdae - schleiferi - sp. - terrae - terregens - testaceum - thalassium - trichothecenolyticum - ulmi - xylanilyticum

Microbispora
amethystogenes - chromogenes - corallina - diastatica - echinospora - griseoalba - mesophila - parva - rosea - sp. - thermodiastatica

Microbulbifer
elongatus - hydrolyticus

Microcella
putealis

Micrococcus
euryhalis - halodurans - infimus - luteus - lylae - sp.

Microlunatus
phosphovorus

Micromonas
micros

Micromonospora
aurantiaca - auratinigra - brunnea - carbonacea - chalcea - chersina - citrea - coerulea - coriariae - eburnea - echinaurantiaca - echinofusca - echinospora - endolithica - flavogrisea - fulviviridis - fulvopurpurea - grisea - hainanense - halophytica - inositola - inyoensis - inyonensis - lacustris - matsumotoense - megalomicea - melanosporea - mirobrigensis - narashino - nigra - olivasterospora - pallida - parva - peucetia - purpurea - purpureochromogenes - rosaria - sagamiensis - sp. - viridifaciens

Micropolyspora
faeni - sp.

Micropruina
glycogenica

Microscilla
arenaria - furvescens - marina - sericea - sp.

Microtetraspora
fusca - glauca - malaysiensis - niveoalba - sp. - viridis

Microvirgula
aerodenitrificans

Millisia
brevis

Mitsuokella
jalaludinii - multacida

Mobiluncus
curtisii - mulieris

Modestobacter
multiseptatus

Moellerella
wisconsensis

Mogibacterium
timidum

Moorella
glycerini - mulderi - thermoacetica - thermoautotrophica

Moraxella
(Branhamella) - (Moraxella) - atlantae - boevrei - bovis - canis - caprae - equi - lacunata - laennata - lincolnii - nonliquefaciens - oblonga - osloensis - saccharolytica - sp. - suis

Morganella
morganii - psychrotolerans

Moritella
abyssi - japonica - marina - profunda - viscosa

Morococcus
cerebrosus

Muricauda
ruestringensis

Muricoccus
roseus

Myceligenerans
crystallogenes - xiligouense

Mycetocola
lacteus - saprophilus - tolaasinivorans

Mycobacterium
abscessus - aemonae - agri - aichiense - album - alvei - angelicum - arupense - asiaticum - aurum - austroafricanum - avium - boenickei - bohemicum - botniense - bovis - branderi - brisbanense - brumae - canariasense - caprae - celatum - chelonae - chimaera - chitae - chlorophenolicum - chubuense - concordense - confluentis - conspicuum - cookii - cosmeticum - diernhoferi - doricum - duvalii - elephantis - fallax - farcinogenes - flavescens - flavum - florentinum - fluoranthenivorans - fortuitum - frederiksbergense - fuerth - gadium - gastri - gilvum - goodii - gordonae - hackensackense - haemophilum - hassiacum - heckeshornense - heidelbergense - hiberniae - hodleri - holsaticum - houstonense - immunogenum - interjectum - intermedium - intracellulare - kansasii - komossense - kubicae - lacus - lentiflavum - madagascariense - mageritense - malmoense - manitobense - marinum - monacense - montefiorense - moriokaense - mucogenicum - murale - nebraskense - neglectum - neoaurum - neworleansense - nonchromogenicum - novocastrense - obuense - palustre - paraffinicum - parafortuitum - parascrofulaceum - paraseoulense - parmense - peregrinum - petroleophilum - phlei - porcinum - poriferae - psychrotolerans - pulveris - pyrenivorans - rhodesiae - saskatchewanense - scrofulaceum - senegalense - seoulense - septicum - shimoidei - simiae - smegmatis - sp. - sphagni - szulgai - terrae - thamnopheos - thermoresistibile - tokaiense - triplex - triviale - tuberculosis - tusciae - vaccae - vanbaalenii - wolinskyi - xenopi - yunnanensis

Mycococcus
luteus - ruber

Mycoplana
bullata - dimorpha - ramosa - sp.

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
flavescens - fulvus - macrosporus - stipitatus - virescens - xanthus