Paenibacillus
Scientific classification
Domain:	Bacteria
Kingdom:	Bacillati
Phylum:	Bacillota
Class:	Bacilli
Order:	Paenibacillales
Family:	Paenibacillaceae
Genus:	Paenibacillus Ash et al., 1994
Species[citation needed]
List P. agarexedens P. agaridevorans P. alginolyticus P. alkaliterrae P. alvei P. amylolyticus P. anaericanus P. antarcticus P. apiarius P. assamensis P. azoreducens P. azotofixans P. barcinonensis P. borealis P. brasilensis P. brassicae[1] P. campinasensis P. chinjuensis P. chitinolyticus P. chondroitinus P. cineris P. cookii P. curdlanolyticus P. daejeonensis P. dendritiformis P. durum P. ehimensis P. elgii P. favisporus P. glucanolyticus P. glycanilyticus P. gordonae P. graminis P. granivorans P. hodogayensis P. illinoisensis P. jamilae P. kobensis P. koleovorans P. koreensis P. kribbensis P. lactis P. larvae P. lautus P. lentimorbus P. macerans P. macquariensis P. massiliensis P. mendelii P. motobuensis P. naphthalenovorans P. nematophilus P. odorifer P. pabuli P. peoriae P. phoenicis P. phyllosphaerae P. polymyxa[2][3][4][5][6][7] P. popilliae P. pulvifaciens P. rhizosphaerae P. sanguinis P. stellifer P. terrae P. thiaminolyticus P. timonensis P. tundrae P. turicensis P. tylopili P. validus P. vortex P. vulneris P. wynnii P. xylanilyticus

Paenibacillus is a genus offacultative anaerobic oraerobic,endospore-formingbacteria, originally included within the genusBacillus, and then reclassified as a separate genus in 1993.^[8] Bacteria belonging to this genus have been detected in a variety of environments, such as soil, water,rhizosphere, vegetable matter, forage, and insect larvae, as well as clinical samples.^{[9][10][11][12]} The name reflects: Latinpaene means almost, so the paenibacilli are literally "almost bacilli". The genus includesP. larvae, which causesAmerican foulbrood inhoneybees,P. polymyxa, which is capable offixing nitrogen, so is used in agriculture and horticulture, thePaenibacillus sp. JDR-2 which is a rich source of chemical agents for biotechnology applications, and pattern-forming strains such asP. vortex andP. dendritiformis discovered in the early '90s,^{[13][14][15][16][17]} which develop complex colonies with intricate architectures^{[18][19][20][21][22]} as shown in the pictures:

• 
  A colony generated by the chiral morphotype bacteria ofP. dendritiformis: The colony diameter is 5 cm and the colors indicate the bacterial density (bright yellow for high density). The branches are curly with well-defined handedness.
• 
  A colony generated byP. vortex sp. bacteria: The colony diameter is 5 cm and the colors indicate the bacterial density (bright yellow for high density). The bright dots are the vortices described in the text.
• 
  A colony generated by the branching (tip splitting) morphotype bacteria ofP. dendritiformis: The colony diameter is 6 cm and the colors indicate the bacterial density (darker shade for higher density).

Interest inPaenibacillus spp. has been rapidly growing since many were shown to be important^[23][24][25] for agriculture and horticulture (e.g.P. polymyxa), industrial (e.g.P. amylolyticus), and medical applications (e.g.P. peoriate). These bacteria produce various extracellular enzymes such as polysaccharide-degrading enzymes and proteases, which can catalyze a wide variety of synthetic reactions in fields ranging from cosmetics tobiofuel production. VariousPaenibacillus spp. also produce antimicrobial substances that affect a wide spectrum of micro-organisms^[26][27][28] such as fungi, soil bacteria, plant pathogenic bacteria, and even important anaerobic pathogens such asClostridium botulinum.

More specifically, severalPaenibacillusspecies serve as efficientplant growth-promoting rhizobacteria (PGPR), which competitively colonize plant roots and can simultaneously act asbiofertilizers and as antagonists (biopesticides) of recognized root pathogens, such as bacteria, fungi, and nematodes.^[29] They enhance plant growth by several direct and indirect mechanisms. Direct mechanisms include phosphate solubilization, nitrogen fixation, degradation of environmental pollutants, and hormone production. Indirect mechanisms include controlling phytopathogens by competing for resources such as iron, amino acids and sugars, as well as by producing antibiotics or lytic enzymes.^[30][31] Competition for iron also serves as a strong selective force determining the microbial population in the rhizosphere. Several studies show that PGPR exert their plant growth-promoting activity by depriving native microflora of iron. Although iron is abundant in nature, the extremely low solubility of Fe³⁺ at pH 7 means that most organisms face the problem of obtaining enough iron from their environments. To fulfill their requirements for iron, bacteria have developed several strategies, including the reduction of ferric to ferrous ions, the secretion of high-affinity iron-chelating compounds, calledsiderophores, and the uptake of heterologous siderophores.P. vortex's genome, for example,^[32] harbors many genes which are employed in these strategies, in particular it has the potential to produce siderophores under iron-limiting conditions.

Despite the increasing interest inPaenibacillus spp., genomic information of these bacteria is lacking. More extensive genome sequencing could provide fundamental insights into pathways involved in complex social behavior of bacteria, and can discover a source of genes with biotechnological potential.

CandidatusPaenibacillus glabratella causes white nodules and high mortality ofBiomphalaria glabrata freshwater snails.^[33] This is potentially important becauseBiomphalaria glabrata is an intermediate host ofschistosomiasis.^[33]

A major challenge in the dairy industry is reducing premature spoilage of fluid milk caused by microbes.^[34]Paenibacillus is often isolated from both raw andpasteurized fluid milk. The most predominantPaenibacillus species isolated isPaenibacillus odorifer. Species in thePaenibacillus genus can sporulate to survive the pasteurization of milk and are subsequently able to germinate in refrigerated milk, despite the low temperatures. Many bacterial genera have acold shock response, which involves the production of cold shock proteins that help the cell facilitate global translation recovery.^[34] Little is currently known about the cold shock response inPaenibacillus compared to other species, but it has been shown thatPaenibacillus species contain many genetic elements associated with the cold shock response.^[35]Paenibacillus odorifer was demonstrated to carry multiple copies of these cold shock associated genetics elements.^[34]

SeveralPaenibacillus species can form complex patterns on semisolid surfaces. Development of such complex colonies requireself-organization and cooperative behavior of individual cells while employing sophisticated chemical communication calledquorum sensing.^{[13][14][18][20][21][36][37][38]} Pattern formation and self-organization in microbial systems is an intriguing phenomenon and reflects social behaviors of bacteria^[37][39] that might provide insights into the evolutionary development of the collective action of cells in higher organisms.^{[13][37][40][41][42][43][44]}

One of the most fascinating pattern formingPaenibacillus species isP. vortex, self-lubricating,flagella-driven bacteria.^[32]P. vortex organizes its colonies by generating modules, each consisting of many bacteria, which are used as building blocks for the colony as a whole. The modules are groups of bacteria that move around a common center at about 10 μm/s.

An additional intriguing pattern formingPaenibacillus species isP. dendritiformis, which generates two different morphotypes^{[13][14][18][19][20][21]} – the branching (or tip-splitting) morphotype and the chiral morphotype that is marked by curly branches with well-defined handedness (see pictures).

These two pattern-formingPaenibacillus strains exhibit many distinct physiological and genetic traits, includingβ-galactosidase-like activity causing colonies to turn blue onX-gal plates andmultiple drug resistance (MDR) (includingtrimethoprim/sulfamethoxazole,penicillin,kanamycin,chloramphenicol,ampicillin,tetracycline,spectinomycin,streptomycin, andmitomycin C). Colonies that are grown on surfaces in Petri dishes exhibit several-fold higher drug resistance in comparison to growth in liquid media. This particular resistance is believed to be due to asurfactant-like liquid front that actually forms a particular pattern on the Petri plate.

• "Paenibacillus Taxonomy".LPSN - List of Prokaryotic names with Standing in Nomenclature.
• "Paenibacillus".Bac Dive - the Bacterial Diversity Metadatabase.
• Prof. Eshel Ben-Jacob home page

• Paenibacillaceae
• Bacteria genera
• Taxa described in 1994

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