TABLE 3.

Cell densities of total bacteria, diazotrophs, clostridia, and phylogenetic populations of clostridia in M. sinensis by the MPN method^a

Tissue	Total no. (cells g−1 of fresh wt)			C/D ratiob (%)	No. of cells (cells g−1 of fresh wt) in phylogenetic populationc
	Bacteria	Diazotrophs	Clostridia		Cluster XIVa	Cluster I
					Group I	Group II	Group IV	Group V
Leaf	2.3 × 105	4.2 × 104	4.2 × 104	100	ND	4.2 × 104	2.6 × 103	1.7 × 104
Stem	2.5 × 106	1.5 × 105	3.5 × 104	23	ND	3.5 × 104	3.5 × 104	1.3 × 103
Root	7.9 × 106	2.9 × 104	1.9 × 104	66	ND	1.9 × 104	6.4 × 103	4.0 × 103

^aSurface sterilization was carried out with 1% NaOCl for 0.5 min for leaves of M. sinensis and 2% NaOCl for 15 min for stems and roots. MPN counts of diazotrophic bacteria and total bacteria were assessed by an acetylene reduction assay and by bacterial growth in MPN tubes containing RMR semisolid medium. Thus, the total number of bacteria indicates the counts of bacteria that can grow only in this medium. TRFLP analysis was performed with cultures that showed cell growth in the MPN tubes. The total number of clostridia was assessed by the maximum population level among individual clostridial groups. The MPN results were single determinations for 150 test tubes.

^bC/D ratio, the ratio of the total number of clostridia to that of diazotrophs.

^cPhylogenetic groups based on 16S rRNA gene sequences (16). Groups I and II are contained in cluster XIVa, as defined by Collins et al. (4). Groups IV and V are included in cluster I (4). ND, not detected (<6 cells g⁻¹ [fresh weight]).