Diversity of prokaryotic microorganisms

It is likely that a vast amount of undiscovered microbial resources exist in the various natural environments of China. However, 2,003 strains of 266 species in 60 genera of bacteria are held in the Chinese Culture Collection Centre affiliated to the Institute of Microbiology, Chinese Academy of Sciences. Due to the lack of a comprehensive survey of the microbial resources of the country, most of these were isolated from samples collected from soil, water, plants and animals. Some of them show considerable promise for industrial and agricultural production.

Over the last forty years, Chinese scientists have carried out systematic surveys of bacterial groups of ecological significance and economic value and social use. The main investigations are as follows:

a. Actinomycetes

Two thousand species in 60 genera of actinomycetes have been identified and recorded in the world up to now. Among these, some species in 40 genera are described and recorded from China; 1,332 cultures of 450 species in 36 genera are preserved. Eight of these genera have been described and recognized by Chinese scientists, i. e., Streptomycoides, Microstreptospora, Actinoalloteichus, Trichotomous, Actinobispora, Planotetraspora, Streptoplanospora and Cathayosporangium. They potentially possess scientific and economic value.

b. Frankia

The Frankia are a group of nitrogen fixing nodulose actinomycetes that can form symbiotic associations with many plants distributed widely in the world. A group of interdisciplinary scientists carried out a national survey on the nodulated actinomycetes in 1978 and discovered that 44 species in 6 genera of plants can form such a symbiosis with Frankia in China. Nineteen of these species are unrecorded in the world, as summarized in Table 1.

Table 1 New species of plant nodulated by Frankia in China

Alnus cremastogyne	E. henryi
A. ferdinandi	E. moorcroftii
A. mandshurica	E. mollis
A. sibirica	E. muliflora var. ovata
Cariaria sinica	E. oxycarpa
C. terminalis	E. stellipila
Elaeagnus bockii	E. umbellata var. pavifolia
E. commutata	Hippophae rhamnoides var. porcera
E. crispa	Myrica nana
E. gonyanthes

c. Rhizobia

Symbiotic nitrogen fixation between rhizobium and leguminous plants represents the most important nitrogen supply system in terrestrial ecosystems, and is the strongest of all biological nitrogen fixation systems. It is estimated that between 1,800 to 1,900 species of leguminous plants exist in the world, and 1,500 of them are recorded from China. Most leguminous plants possess a nodule formation capacity by rhizobium and effect nitrogen fixation. Fifteen species in 4 genera have been documented internationally. Based on the survey in China, almost 2,000 cultures have been isolated and purified in rhizobium groups and a new genus, Sinorhizobium, was identified and which includes two new species. In addition, the rhizobia that form nodules on the root of Astragalus sinicus were named Rhizobium huakuii. A new species isolated from the arid area of Xinjiang was named Rhizobium tianshanellse. The ultra-slowly growing rhizobia isolated from the root nodules of soybean were named Bradyrhizobium liaoningense. Mesorhizobium is new genus which was discovered recently in China.