Spatial Distribution and Controlling Factors on the Bacterial Abundance in the Indian Groundwaters

  

    
Parameter
    
Depth
    
Temp
    
DO Sat
    
BR
    
pCO2
    
TDCHO
    
TDFAA
    
TDPRO
    
TVC
    
A
    
E
    
P
    
K#
  
  

    
Depth
    
--
    
-0.57***
    
-0.51***
    
-0.16
    
0.19
    
-0.12
    
0.30*
    
-0.1
    
-0.85***
    
-0.86***
    
-0.58***
    
-0.67***
    
-0.45**
  
  

    
Temp
    

    
--
    
0.43**
    
0.39*
    
-0.34*
    
0.49**
    
-0.22
    
0.23
    
0.52***
    
0.09
    
0.32*
    
0.25***
    
0.21
  
  

    
DO Sat
    

    

    
--
    
0.16
    
-0.2
    
0.06
    
-0.19
    
-0.2
    
-0.30*
    
-0.19
    
-0.30*
    
0.26
    
-0.57***
  
  

    
BR
    

    

    

    
--
    
-0.27
    
0.17
    
-0.12
    
0.34*
    
0.45**
    
0.31*
    
0.35*
    
0.32*
    
-0.35*
  
  

    
pCO2
    

    

    

    

    
--
    
-0.03
    
0.25
    
0.42**
    
0.32*
    
0.62***
    
0.30*
    
0.38*
    
0.42**
  
  

    
TDCHO
    

    

    

    

    

    
--
    
0.23
    
-0.45**
    
-0.45**
    
-0.30*
    
-0.58***
    
-0.55***
    
-0.25
  
  

    
DFAA
    

    

    

    

    

    

    
--
    
-0.12
    
-0.42**
    
-0.35*
    
-0.54***
    
-0.31*
    
-0.61***
  
  

    
TDPRO
    

    

    

    

    

    

    

    
--
    
-0.35*
    
-0.43**
    
-0.32*
    
-0.56***
    
-0.31*
  
  

    
TVC
    

    

    

    

    

    

    

    

    
--
    
0.41**
    
0.35*
    
0.41**
    
0.79***
  
  

    
A
    

    

    

    

    

    

    

    

    

    
--
    
--
    
--
    
--
  
  

    
E
    

    

    

    

    

    

    

    

    

    

    
--
    
--
    
--
  
  

    
P
    

    

    

    

    

    

    

    

    

    

    

    
--
    
--
  
  

    
K
    

    

    

    

    

    

    

    

    

    

    

    

    
--
  
  

    
***p <0.001; **p <0.01; *p    <0.05. #indicates the correlations taken for only two states    (KL and MH). 
  

Table 3: Rank and correlation matrix (Spearman’s, r) of different properties in Indian coastal ground waters during monsoon period.

Discussion

Variability in bacterial cells and their possible sources into the groundwater

Groundwater can be contaminated in several ways, natural and anthropogenic. In the natural processes, groundwater is contaminated because of rock weathering, organic matter decomposition, and leaching of inorganic compounds, organic compounds, and microorganisms during the monsoon season. Anthropogenic sources contain mainly septic sewage disposal, agricultural waste, and industrial and domestic waste in open lands. Several studies on groundwater quality noticed that groundwater’s biological contamination mostly occurs through septic sewage and open dump yards [14,15]. India is the second-largest country in the population (1,390,508,600) after China. In the last decade, the Indian population has increased from 123.1 crores to 137.5 crores; concerning enhancement in population, the amount of sewage production also increased. Central pollution control board (https://cpcb.nic.in/status-of-stps) reported that sewage treatment plants have increased from 450 to 1760 in the last ten years all over India (http://www.sulabhenvis.nic.in/Database/ STST_wastewater_2090.aspx). However, most of the rural and urban regions are still using septic tanks at homes. The sewage produced from these is not included in the plants as mentioned above count. A few research studies reported that the sewage from the septic tank could also be used for recycling of water for irrigation and the sludge used as fertilizer for the crop, in such cases, there are many chances for groundwater to be contaminated in more porous regions [16,17]. In some areas, this septic tank sewage is dumping in the ponds and lagoons, which has a significant effect on the groundwater contamination with microbes [18]. Along with this, septic tanks and soakaways increased drastically in housing, public apartments, and industries as the population increased day by day. This may lead to an increase in the seepage of sewage into groundwater through soil [16], so all these practices are contaminating the groundwater chemically and biologically. Al-Bahry et al. [16] noticed that bacteria in sewage sludge remain viable for several days to weeks if that kind of material is used as fertilizers; consequently, microbial contamination increases in the environment.

E. coli is one of the most commonly found bacteria in any aquatic system, especially in groundwater, and it is a good indicator of the presence of pathogens in groundwater. In Indian coastal groundwater on the east coast, 40% and 30% of groundwater are contaminated with these bacterial groups on the west coast. OD and WB have the highest E. coil count on the east coast, and KA and GA have the highest count on the west coast. Not only in Indian groundwater but also there are several countries facing problems with E. coli contamination in groundwater, USA [19], UK, Finland) [20], Ireland [21], Canada [22]. E. coli or coliform bacteria is not identified in any 100mL of drinking water sample [23] standards for microbiological quality of drinking water [24]. E. coli O157:H7 is a faecal pathogen that is regularly isolated from water [25] and identified as the primary cause of gastrointestinal illness outbreaks [26]. Several studies noticed that these bacteria could also survive in warm and cold and nutrient starving conditions [27].

Achromobacter sp. are found in the groundwater of WB, AP, GJ, KA, KL, TN states and these bacteria are well known for oxidation of arsenite to arsenate in the groundwater [28]. This bacterium was found more in the west coast groundwater (40%) than in the east (25%). Fertilizers, pesticides, and herbicides, which are used for agricultural purposes, contain a high percentage of arsenic it may contaminate the groundwater with arsenic in these regions. Shahina et al. [29] noticed that majority of the area in Indian states are significantly contaminated with arsenic (As) pollution and also found the highest contamination in WB (20%), GJ (5%), KA (0.5%), KL (0.5%), and OD (0.4%), AP, TN, and MH with (0.1%). The two most prevalent clinical manifestations of Achromobacter sp. infections in non-CF hosts are pneumonia and bacteremia [30]. Skin and soft tissue infections, urinary tract infections, intra-abdominal organ infections, Central Nervous System (CNS), eye and ear infections are less common, with endocarditis and bone infections being extremely rare [31].

Pseudomonas aeruginosa is more common in the west coast region (20%), especially in Karnataka and Goa state groundwater and on the east coast (8%) in Odisha and Tamil Nadu state groundwater. Pseudomonas aeruginosa is a prevalent pathogen found in faeces, soil, water, and sewage. It can multiply in water settings and on the surface of appropriate organic materials in contact with water. Pseudomonas aeruginosa is a well-known source of hospital-acquired infections that can lead to significant consequences. It was insulated from various wet surroundings, including sinks, water baths, hot water systems, showers, and spa pools [32]. Pseudomonas aeruginosa can cause deadly progressive lung infections. Warm, wet surroundings, such as swimming pools and spas, are connected with water-related folliculitis and ear infections. Many strains are resistant to various antimicrobial treatments, which increases the organism’s importance in medical settings [33]. Shahina et al. [29] noticed that most southeast coast groundwater is contaminated with Pseudomonas aeruginosa. This could be possible due to the open dumping of waste, which causes groundwater contamination with microbes.

Klebsiella sp. is the least abundant bacterial group found in Indian coastal groundwater. This is only noticed in west coast groundwater and two states, Kerala (12%) and Maharashtra (14%). This bacterium is the natural occupant of many aquatic settings. They may reproduce rapidly in nutrient-rich fluids such as pulp mill effluent, textile finishing factories, and sugar-cane processing facilities. They are known to colonize tap washers in drinking-water distribution systems. Organisms can develop in water distribution networks. Klebsiella sp. are also found in the faeces of many healthy animals, and they can be found in sewage-contaminated water [34]. Bartram [33] noticed that Klebsiella sp. was infecting hospital patients, with dissemination linked to frequent patient handling (e.g., in intensive care units). Patients with compromised immune systems, such as the elderly or very young, patients with burns or extensive wounds, those on immunosuppressive medicine, or those infected with HIV/AIDS, are at the greatest danger.

Factors affecting the distribution of bacteria in coastal groundwater

Several biogeochemical properties significantly impact the distribution of bacterial count in the coastal groundwater along the Indian coast. A significant inverse linear relation between Total Viable Count (TVC) to depth (r² = 0.85, p<0.001; Table 3), and a significant linear positive relation between TVC and temperature (r² =0.52, p<0.001; Table 3), which is suggesting that the bacterial number decreasing with depth and warm groundwater has more bacterial count than low-temperature waters. East coast groundwater has warm temperatures and high TVC (Table 1). TVC also shows a significant positive relations with bacterial respiration (r² = 0.45, p<0.01; Table 3) and pCO2 (r² =0.32, p<0.05; Table 3), and inverse relation with labile organic compounds such as total dissolved carbohydrates (TDCHO; r² = 0.45, p<0.01), total dissolved amino acids (TDFAA; r² = 0.42, p<0.01; Table 3), total dissolved proteins (TDPRO; r² = 0.35, p<0.05; Table 3). The linear positive relations with BR and pCO₂ and inverse relations with labile organic compounds of TVC, suggesting that bacteria utilized the available labile organic compounds significantly for their growth in coastal groundwater (Figure 5). The presence of high bacteria (TVC (CFU/ml): 7.1x10³±6.6x10³; Table 2) along the east coast groundwater is may be due to the high availability of labile organic compounds such as TDCHO (1.16±0.10 mg/l; Table 2), TDFAA (0.30±0.12 mg/l; Table 2), and TDPRO (0.90±0.3mg/l; Table 2), which also associated with high bacterial respiration rates in the east coast (4.33±3.14mg/l/h; Table 2) than west coast (2.87±2.93 mg/l/h; Table 2) groundwater along the Indian coast. Achromobacter sp. showed a significant relation with TDPRO than TDCHO and TDFAA, suggesting that these bacteria utilizing more proteinaceous food than TDCHO and TDFAA (Table 3; Figure 5). E. coli O157:H7 showed significant relations with TDCHO and TDFAA among three compounds, indicating that these bacteria may be more dependent on these two compounds for their growth (Table 3; Figure 5). Pseudomonas aeruginosa bacteria showed significant relation with TDCHO and TDPRO compounds, suggesting that these bacteria may consume them to meet their growth requirements (Table 3; Figure 5). (Any references supporting this will be useful).

    

    

    Figure 5: Principal component analysis of different controlling factors on
bacterial distribution in Indian coastal ground waters during the monsoon
period.