Cupriavidus necator
H16 is an ideal strain for polyhydroxybutyrate (PHB) production from CO
2
. Low-oxygen-stress can induce PHB synthesis in
C. necator
H16 while reducing bacterial growth under chemoautotrophic culture. The optimum growth and PHB synthesis of
C. necator
H16 cannot be achieved simultaneously, which restricts PHB production. The present study was initiated to address the issue through comparative transcriptome and gene function analysis. Firstly, the comparative transcriptome of
C. necator
H16 chemoautotrophically cultured under low-oxygen-stress and non-stress conditions was studied. Three types of transcription different genes were discovered: PHB enzymatic synthesis, PHB granulation, and regulators. Under low-oxygen-stress condition, acetoacetyl-CoA reductase gene
phaB2
, PHB synthase gene
phaC2
, phasins genes
phaP1
and
phaP2
, regulators genes
uspA
and
rpoN
were up-regulated 3.0, 2.5, 1.8, 2.7, 3.5, 1.6 folds, respectively. Secondly, the functions of up-regulated genes and their applications in PHB synthesis were further studied. It was found that the over-expression of
phaP1
,
phaP2
,
uspA
, and
rpoN
can induce PHB synthesis under non-stress condition, while
phaB2
and
phaC2
have no significant effect. Under the optimum condition, PHB percentage content in
C. necator
H16 was respectively increased by 37.2%, 28.4%, 15.8%, and 41.0% with the over-expression of
phaP1
,
phaP2
,
uspA
, and
rpoN
, and the corresponding PHB production increased by 49.8%, 42.9%, 47.0%, and 77.5% under non-stress chemoautotrophic conditions. Similar promotion by
phaP1
,
phaP2
,
uspA
, and
rpoN
was observed in heterotrophically cultured
C.
necator
H16. The PHB percentage content and PHB production were respectively increased by 54.4% and 103.1% with the over-expression of
rpoN
under non-stress heterotrophic conditions.
Importance
Microbial fixation of CO
2
is an effective way to reduce greenhouse gases. Some microbes such as
C. necator
H16 usually accumulate PHB when they grow under stress. Low-oxygen-stress can induce PHB synthesis when
C. necator
H16 is autotrophically cultured with CO
2
, H
2
, and O
2
, while under stress, growth is restricted and total PHB yield is reduced. Achieving the optimal bacterial growth and PHB synthesis at the same time is an ideal condition for transforming CO
2
into PHB by
C. necator
H16. The present study was initiated to clarify the molecular basis of low-oxygen-stress promoting PHB accumulation and to realize the optimal PHB production by
C. necator
H16. Genes up-regulated under non-stress conditions were identified through comparative transcriptome analysis and over-expression of phasin and regulator genes were demonstrated to promote PHB synthesis in
C. necator
H16.