Path analysis for factors affecting the growth and nitrogen conversion of Bacillus in low-nutrition-level water conditions

[Methods] Thus, in the present study, hydrolytic and bacteriostatic activities of two Bacullisstrains NT9 and YB3 were determined by using plate methods. Thereafter, four low-nutrition-level water conditions were prepared artificially, and the effects of characteristics of Bacillusstrains and environments on bacterial growth and nitrogen conversion were researched simultaneously, by separating out the total, direct and indirect effects of both aspects were with path analysis method.

[Results] Results showed that unlike B. cereusstrain YB3, strain NT9 was a B.subtilispossessed stronger proteolytic, amylolytic and bacteriostatic activities but with a weaker cellulase activity. However, as similar as strain YB3, strain NT9 could degrade organic nitrogen and ammonia, with a high of the ammonia-conversion rate of 89.3% under low nutrition condition. Results from path analysis showed that in models the main goodness-of-fit indices were all suitable, with high determination coefficients (R²) of 0.55-0.95. The cellulase activity (cel) of Bacillusstrains displayed significant direct positive effects on bacterial growth (gro) and degradations of organic nitrogen and ammonia (dtan) in most of the four water conditions (P<0.001). The environmental factors, such as the initial bacterial counts (iod), organic nitrogen content (ion), ammonia content (itann) and time duration phase (stage) also executed significant direct positive effects on groand dtan(P<0.05), but only for some special conditions. There were interactions among Bacillusactivities and environmental factors, which produced indirect effects on groand dtan, and in turn reinforced or weakened their direct effects, resulting in final significant (P<0.05) or non-significant (P>0.05) total effects of factors. Meanwhile, in some environments, groand dtancould significantly and directly improved each other (P<0.001), or produced indirect effects on each other.

[Conclusions] In conclusion, the characteristics of strain and environment could intensively affect the growth and nitrogen conversion of Bacillus,with different pattern in different water conditions, indicating that for better application of Bacillus, strategies should be made and adjusted according to water conditions, such as dosages and durations of strain and nitrogen sources.