Connection of metabolites with microbial diversity in different
fallow periods and Rhizopshere niches, RI and BS
In our study, specific functional groups were more represented in
different niches. The affiliation of the sequences in the KEGG database
and further analysis in STAMP indicated the metabolism-related with ’ABC
transporter,’ ’Amino acid and sugar metabolites metabolism,
’Lipopolysaccharides biosynthesis, ’pyruvate metabolism’ in theJhum field soil.
ABC transporter re involved in the secretion of phytochemicals present
in the root exudates in most plants (50-53). Any mutation in the ABC
transporter alters the root exudation of phytochemicals, which in turn
changes the microbial diversity near the plant root rhizosphere (54). In
the bacterial system, it helps in nutrient uptake as well as in the
secretion of toxins and antimicrobial agents. In a comparative study, we
have found that in bulk soil where there is no influence of crop roots,
there is a higher presence of ABC transporters in 5 years than in 20
years fallow periods (Fig. 7 a,b,c,d). This may be attributed to the
high stress put by the bacterial community to make the soil stable,
unlike the soil in a long fallow period, which is already in a stable
state. A similar pattern was observed in the case of LARS (Fig. 7 b);
however, the ABC transporter in SARS and RI is opposite and is higher in
the case of the long fallow period (Fig 7 c,d). Interestingly, it has
been found that the phylum Proteobacteria is abundant in thejhum fields irrespective of the crop, rhizosphere niches, or the
fallow period (Fig. 2 a,b,c,d). Proteobacteria , along with other
soil phyla such as Bacteroides and Acidobacteria, uses the
ABC transporter as an active transport system (55).
Our study has found greater amino and nucleotide sugar metabolism gene
abundance in fields with a long fallow period of LARS (Fig. 7b) and BS
(Fig. 7a) as compared to the short fallow periods of SARS (Fig. 7c) and
RI (Fig 7 d). The amino and nucleotide sugar indicates the soil
microbial community composition. It has been reported that any change in
the ratio of the amino and nucleotide sugars can be used as a
qualitative indicator of time-integrated compositional changes in the
soil microbial community (56, 57).
Lipopolysaccharides are complex glycolipids attached to the outer
membrane of most Gram-negative bacterial cells (58). These compounds aid
soil stability by ”gluing” soil particles together (59). Bacteria use
these compounds for attachment to soil particles, promoting the
formation of soil aggregates (60, 61). In the jhum field
ecosystem, we have found that the long fallow periods in the BS, LARS,
and SARS have more lipopolysaccharide metabolism than short fallow
periods (Fig. 7 a,b,c). This indicates that the long fallow periods have
more soil aggregating propensity than the shorter fallow periodsjhum fields. In the case of the pyruvate metabolism, while RI
follows a similar trend to lipopolysaccharides metabolism (Fig. 7d),
however, it is predominant in the BS, LARS, and SARS of short fallow
periods than the long fallow period(Fig 7a,b,c). Pyruvate is a vital
intersection in the network of metabolic pathways that unites several
vital metabolic processes in both aerobic and anaerobic bacteria (62).
Our finding suggests more pyruvate metabolism in the short fallow
periods.
Another interesting observation is the high sequence abundance for
benzoate in long fallow periods of SARS and RI as compared to the short
fallow periods, while the pattern is opposite for LARS and BS. Benzoate
is a xenobiotic compound (63). Soil microorganisms collectively
decompose such compounds to the mineral salts, which are then utilized
by plants (64). Some of the bacterial family-likeSyntrophobacteraceae, Helicobacteraceae, which belongs toProteobacteria phylum, were reported for the benzoate degradation
(65), and it was found in the jhum field soil mainly in short
fallow periods of LARS and BS. Clostridiales were more
predominant in the long fallow periods of SARS and RI, which is also
reported for benzoate degradation (65).
In general, our result suggests that the metabolite profile is regulated
by the microbial communities present in the different rhizosphere niches
of jhum field soil.