坏疽梭杆菌

Metabolism.

代谢。

The core metabolism of Fusobacterium nucleatum is similar to that of Clostridium, Lactococcus,

and Enterococcus species (Kapatral et al., 2002). More than 137 transporters

for the uptake of

substrates such as peptides, sugars, metal ions, and cofactors have been detected. Amino acids

and small peptides comprise the major sources of energy for all Fusobacterium species (Gharbia

and

H.N.

Shah,

1989),

however,

peptides

influence

the

uptake

of

amino

acids

enhancing

the

utilization

of

histidine

and

glutamate

while

threonine,

methionine,

and

asparagine

were

repressed (Gharbia et al., 1989). Acidic and cationic amino acids are the main acids incorporated.

Glutamate,

histidine,

lysine,

and

serine

appear

to

be

key

amino

acids

in

Fusobacterium

nucleatum

(Gharbia

and

Shah,

1991a;

Rogers

et

al.,

1992).

Biosynthetic

pathways

exist

for

glutamate, aspartate, and glutamylglutamate to be used as growth substrates for Fusobacterium

nucleatum (Takahashi and Sato, 2002). Glutamate is a key catabolic substrate in Fusobacterium

species

(Gharbia

and

Shah,

1991b).

It

is

catabolized

via

the

2-oxoglutarate

pathway

with

the

production of acetate and butyrate as end products (Gharbia and Shah, 1991b). Glutamate may

also be degraded by the methylaspartate pathway in Fusobacterium varium (Gharbia and Shah,

1991b). Enzymes representative for the mesaconate pathway for catabolism of glutamate have

been detected in Fusobacterium varium, Fusobacterium mortiferum, and Fusobacterium ulcerans

(Gharbia and Shah, 1991b). Fusobacterium varium and Fusobacterium mortiferum also possess

enzymes

representative

of

the

4-aminobutyrate

pathway.

Amino

acids

are

imported

as

monomers,

di-,

or

oligopeptides,

and

an

active

transport

of

the

dipeptide

l-cysteinglycine

has

been detected in Fusobacterium nucleatum (Carlsson et al., 1994).

Fusobacterium species differ in their ability to use fermentable carbohydrates as energy sources

for growth (Robrish et al., 1991). Fusobacterium nucleatum and other species utilize glucose for

biosynthesis

of

intracellular

glycopolymers

that

can

be

degraded

to

produce

energy

under

conditions

of

amino-acid

deprivation

(Robrish

et

al.,

1987).

The

accumulation

of

glucose

is

dependent

on

energy

generated

by

the

fermentation

of

amino

acids

(Robrish

et

al.,

1987).

Fusobacterium

mortiferum

is

an

exception

in

that

accumulation

of

sugars

is

independent

of

a

fermentable

amino

acid.

Significantly,

Fusobacterium

mortiferum

has

the

ability

to

metabolize

various sugars as energy sources for growth (Robrish et al., 1991). Sugars utilized include a- and

b-glycosides,

which

are

transported

by

the

phosphoenolpyruvate- dependent

sugar:

phosphotransferase system. Thus, it utilizes sucrose and its isomeric a-d-glucosyl-d- fructoses as

energy

sources

for

growth

(Pikis

et

al.,

2002).

The

genes

encoding

phospho-b- glucosidase

(P-b-glucosidase;

EC

3.22.1.86)

and

6-phospho-a-d-glucosidase

(maltose-6phosphate

hydrolase;

EC

3.2.1.122)

known

as

pbgA

and

malH,

respectively,

have

been

expressed

in

Escherichia

coli

(Bouma et al., 1997; Thompson et al., 1997).

具核梭杆菌代谢的核心是类似的梭状芽孢杆菌，

乳酸菌，

肠球菌属

（

kapatral

等人。

，

2002

）

。

超过

137

< br>的转运底物如肽，糖，金属离子的吸收，

和辅因子被发现。氨基酸和小肽包括所有

梭杆菌属的主要能源（西部和铬

Shah

，

1989

）

，然而，影响氨基酸肽 增强组氨酸和谷氨酸的

摄取利用，苏氨酸，蛋氨酸，和天冬酰胺被压抑（西部等人。

，

1989

）

。酸 性和阳离子氨基酸

是主要的酸。

谷氨酸，

赖氨酸，

丝氨酸，

组氨酸，

似乎具核 梭杆菌关键氨基酸

（西部和

Shah

，

1991a

；

Rogers